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Return Empty Array in C# If Index In Loop is Out Of Range [duplicate]

This question already has an answer here:
Index Error in C# Where Array Should Return Empty Array But Returns Out Of Range
(1 answer)
Closed 2 years ago.
I'm new to C# and what I want to do here is add a conditional to return an empty array if the loop that I have set for my DataPoints API response variable is out of range.
Right now it throws an exception but what I want it to do is instead of throwing the exception just return an empty array in the DataPoints API response. How would I do that?
exception
"Index was out of range. Must be non-negative and less than the size
of the collection.\r\nParameter name: index""
code sample
public void BuildDataPoints()
{
// Create WspViewList from ViewData
WspViewList dataPointBuilder = new WspViewList(ViewData);
List<DataPointAPI> dataset = new List<DataPointAPI>();
WspViewCol _labelCol = null;
List<WspViewCol> yAxisCols = new List<WspViewCol>();
//Iterate through the view's columns to find special chart columns
foreach (WspViewCol col in dataPointBuilder._cols)
{
if (col._baseCol.DbrViewCol.YAxis)
yAxisCols.Add(col);
if (col._baseCol.DbrViewCol.XAxis)
_labelCol = col;
}
var DataPoints = new DataPoints();
// Generate DataPoints (or something similar) from the newly constructed WspViewList.
foreach (WspViewRow row in dataPointBuilder)
{
var dataPointList = row.OriginalData.TrimStart('[').TrimEnd(']').Split(',').ToList();
for (var index = 2; index < dataPointList.Count; index++)
{
var dataPoint = dataPointList[index];
if (string.IsNullOrEmpty(dataPoint))
continue;
ChartDataObject cdo;
if (DataPoints.datasets.Count <= index - 2)
{
cdo = new ChartDataObject();
DataPoints.datasets.Add(cdo);
cdo.label = ColumnObjects[index].propertyName;
}
else
cdo = DataPoints.datasets[index - 2];
cdo.data.Add(dataPoint);
<—-THIS LINE THROWS THE ERROR —>
DataPoints.datasets[index - 2] = cdo;
}
DataPointAPI DataPointResponse = new DataPointAPI()
{
data = DataPoints,
};
dataset.Add(DataPointResponse);
}
// Set some class field to contain these datapoints
ChartData = dataset;
}
public class DataPointAPI
{
public DataPoints data;
}
public class DataPoints
{
public List<string> labels { get; set; }
public List<ChartDataObject> datasets { get; set; }
public DataPoints()
{
labels = new List<string>();
datasets = new List<ChartDataObject>();
}
}
public class ChartDataObject
{
public string label { get; set; }
public List<string> data { get; set; }
public ChartDataObject()
{
data = new List<string>();
}
}

Before whichever line of code causes the error, put something like:
if(someIndex >= someArray.Length)
return new someType[someLengthYouWantTheNewArrrayToHave];
Change the names for whatever is relevant to your code (it isn't really easy to see which line of code throws this error you encounter). It's also not clear to me what you mean by "empty array" - usually it's either an array with length 0, bllut people sometimes mean an array where every element is null or zero. The essential logic is "if the index is at or greater than the array length, you're about to crash so do something else instead, like returning new string[2]". You'll also need to make sure that the return type of the method your code is in matches the type of the array you return.
I didn't recommend catching the exception because exceptions are expensive. If you can prevent raising them by detecting when you're about to access an array/collectionnusing an index that is greater than its length, then you should rather than trying code you know will crash and catching. Using exceptions for normal control flow is generally a no-no

Declare a function that does the job:
public DataPointAPI ProcessWspViewRow(WspViewRow) {
DataPointAPI DataPointResponse = new DataPointAPI();
var dataPointList = row.OriginalData.TrimStart('[').TrimEnd(']').Split(',').ToList();
if (dataPointList.Count < 2) {
// Assign here DataPointResponse.data = new DataPoints();
return DataPointResponse;
}
DataPoints.labels.Add(dataPointList[1]);
for (var index = 2; index< dataPointList.Count; index++)
{
var dataPoint = dataPointList[index];
if (string.IsNullOrEmpty(dataPoint))
continue;
ChartDataObject cdo;
if (DataPoints.datasets.Count <= index - 2)
{
cdo = new ChartDataObject();
DataPoints.datasets.Add(cdo);
cdo.label = ColumnObjects[index].propertyName;
}
else
cdo = DataPoints.datasets[index - 2];
cdo.data.Add(dataPoint);
DataPoints.datasets[index - 2] = cdo;
}
DataPointResponse.data = DataPoints;
return DataPointResponse
}
Your code now becomes:
foreach (WspViewRow row in dataPointBuilder)
{
dataset.Add(ProcessWspViewRow(row);
}

Try this:
try
{
// your code
}
catch (IndexOutOfRangeException)
{
return Array.Empty<T>();
}
Where T is type of your array element.

Getting a "System.IndexOutOfRangeException" [duplicate]

How do I check to see if a column exists in a SqlDataReader object? In my data access layer, I have create a method that builds the same object for multiple stored procedures calls. One of the stored procedures has an additional column that is not used by the other stored procedures. I want to modified the method to accommodate for every scenario.
My application is written in C#.

public static class DataRecordExtensions
{
public static bool HasColumn(this IDataRecord dr, string columnName)
{
for (int i=0; i < dr.FieldCount; i++)
{
if (dr.GetName(i).Equals(columnName, StringComparison.InvariantCultureIgnoreCase))
return true;
}
return false;
}
}
Using Exceptions for control logic like in some other answers is considered bad practice and has performance costs. It also sends false positives to the profiler of # exceptions thrown and god help anyone setting their debugger to break on exceptions thrown.
GetSchemaTable() is also another suggestion in many answers. This would not be a preffered way of checking for a field's existance as it is not implemented in all versions (it's abstract and throws NotSupportedException in some versions of dotnetcore). GetSchemaTable is also overkill performance wise as it's a pretty heavy duty function if you check out the source.
Looping through the fields can have a small performance hit if you use it a lot and you may want to consider caching the results.

The correct code is:
public static bool HasColumn(DbDataReader Reader, string ColumnName) {
foreach (DataRow row in Reader.GetSchemaTable().Rows) {
if (row["ColumnName"].ToString() == ColumnName)
return true;
} //Still here? Column not found.
return false;
}

In one line, use this after your DataReader retrieval:
var fieldNames = Enumerable.Range(0, dr.FieldCount).Select(i => dr.GetName(i)).ToArray();
Then,
if (fieldNames.Contains("myField"))
{
var myFieldValue = dr["myField"];
...
Edit
Much more efficient one-liner that does not requires to load the schema:
var exists = Enumerable.Range(0, dr.FieldCount).Any(i => string.Equals(dr.GetName(i), fieldName, StringComparison.OrdinalIgnoreCase));

I think your best bet is to call GetOrdinal("columnName") on your DataReader up front, and catch an IndexOutOfRangeException in case the column isn't present.
In fact, let's make an extension method:
public static bool HasColumn(this IDataRecord r, string columnName)
{
try
{
return r.GetOrdinal(columnName) >= 0;
}
catch (IndexOutOfRangeException)
{
return false;
}
}
Edit
Ok, this post is starting to garner a few down-votes lately, and I can't delete it because it's the accepted answer, so I'm going to update it and (I hope) try to justify the use of exception handling as control flow.
The other way of achieving this, as posted by Chad Grant, is to loop through each field in the DataReader and do a case-insensitive comparison for the field name you're looking for. This will work really well, and truthfully will probably perform better than my method above. Certainly I would never use the method above inside a loop where performace was an issue.
I can think of one situation in which the try/GetOrdinal/catch method will work where the loop doesn't. It is, however, a completely hypothetical situation right now so it's a very flimsy justification. Regardless, bear with me and see what you think.
Imagine a database that allowed you to "alias" columns within a table. Imagine that I could define a table with a column called "EmployeeName" but also give it an alias of "EmpName", and doing a select for either name would return the data in that column. With me so far?
Now imagine that there's an ADO.NET provider for that database, and they've coded up an IDataReader implementation for it which takes column aliases into account.
Now, dr.GetName(i) (as used in Chad's answer) can only return a single string, so it has to return only one of the "aliases" on a column. However, GetOrdinal("EmpName") could use the internal implementation of this provider's fields to check each column's alias for the name you're looking for.
In this hypothetical "aliased columns" situation, the try/GetOrdinal/catch method would be the only way to be sure that you're checking for every variation of a column's name in the resultset.
Flimsy? Sure. But worth a thought. Honestly I'd much rather an "official" HasColumn method on IDataRecord.

Here is a working sample for Jasmin's idea:
var cols = r.GetSchemaTable().Rows.Cast<DataRow>().Select
(row => row["ColumnName"] as string).ToList();
if (cols.Contains("the column name"))
{
}

The following is simple and worked for me:
bool hasMyColumn = (reader.GetSchemaTable().Select("ColumnName = 'MyColumnName'").Count() == 1);

This works for me:
bool hasColumnName = reader.GetSchemaTable().AsEnumerable().Any(c => c["ColumnName"] == "YOUR_COLUMN_NAME");

I wrote this for Visual Basic users:
Protected Function HasColumnAndValue(ByRef reader As IDataReader, ByVal columnName As String) As Boolean
For i As Integer = 0 To reader.FieldCount - 1
If reader.GetName(i).Equals(columnName) Then
Return Not IsDBNull(reader(columnName))
End If
Next
Return False
End Function
I think this is more powerful and the usage is:
If HasColumnAndValue(reader, "ID_USER") Then
Me.UserID = reader.GetDecimal(reader.GetOrdinal("ID_USER")).ToString()
End If

If you read the question, Michael asked about DataReader, not DataRecord folks. Get your objects right.
Using a r.GetSchemaTable().Columns.Contains(field) on a DataRecord does work, but it returns BS columns (see screenshot below.)
To see if a data column exists AND contains data in a DataReader, use the following extensions:
public static class DataReaderExtensions
{
/// <summary>
/// Checks if a column's value is DBNull
/// </summary>
/// <param name="dataReader">The data reader</param>
/// <param name="columnName">The column name</param>
/// <returns>A bool indicating if the column's value is DBNull</returns>
public static bool IsDBNull(this IDataReader dataReader, string columnName)
{
return dataReader[columnName] == DBNull.Value;
}
/// <summary>
/// Checks if a column exists in a data reader
/// </summary>
/// <param name="dataReader">The data reader</param>
/// <param name="columnName">The column name</param>
/// <returns>A bool indicating the column exists</returns>
public static bool ContainsColumn(this IDataReader dataReader, string columnName)
{
/// See: http://stackoverflow.com/questions/373230/check-for-column-name-in-a-sqldatareader-object/7248381#7248381
try
{
return dataReader.GetOrdinal(columnName) >= 0;
}
catch (IndexOutOfRangeException)
{
return false;
}
}
}
Usage:
public static bool CanCreate(SqlDataReader dataReader)
{
return dataReader.ContainsColumn("RoleTemplateId")
&& !dataReader.IsDBNull("RoleTemplateId");
}
Calling r.GetSchemaTable().Columns on a DataReader returns BS columns:

TLDR:
There are lots of answers with claims about performance and bad practice, so I clarify that here.
The exception route is faster for higher numbers of returned columns, the loop route is faster for lower number of columns, and the crossover point is around 11 columns. Scroll to the bottom to see a graph and test code.
Full answer:
The code for some of the top answers work, but there is an underlying debate here for the "better" answer based on the acceptance of exception handling in logic and its related performance.
To clear that away, I do not believe there is much guidance regarding catching exceptions. Microsoft does have some guidance regarding throwing exceptions. There they do state:
Do not use exceptions for the normal flow of control, if possible.
The first note is the leniency of "if possible". More importantly, the description gives this context:
framework designers should design APIs so users can write code that does not throw exceptions
That means, if you are writing an API, that might be consumed by somebody else, give them the ability to navigate an exception without a try/catch. For example, provide a TryParse with your exception-throwing Parse method. Nowhere does this say though that you shouldn't catch an exception.
Further, as another user points out, catches have always allowed filtering by type and somewhat recently allow further filtering via the when clause. This seems like a waste of language features if we're not supposed to be using them.
It can be said that there is some cost for a thrown exception, and that cost may impact performance in a heavy loop. However, it can also be said that the cost of an exception is going to be negligible in a "connected application". Actual cost was investigated over a decade ago: How expensive are exceptions in C#?
In other words, the cost of a connection and query of a database is likely to dwarf that of a thrown exception.
All that aside, I wanted to determine which method truly is faster. As expected there is no concrete answer.
Any code that loops over the columns becomes slower as the number of columns increase. It can also be said that any code that relies on exceptions will slow depending on the rate in which the query fails to be found.
Taking the answers of both Chad Grant and Matt Hamilton, I ran both methods with up to 20 columns and up to a 50% error rate (the OP indicated he was using this two test between different stored procedures, so I assumed as few as two).
Here are the results, plotted with LINQPad:
The zigzags here are fault rates (column not found) within each column count.
Over narrower result sets, looping is a good choice. However, the GetOrdinal/Exception method is not nearly as sensitive to number of columns and begins to outperform the looping method right around 11 columns.
That said, I don't really have a preference performance wise as 11 columns sounds reasonable as an average number of columns returned over an entire application. In either case we're talking about fractions of a millisecond here.
However, from a code simplicity aspect, and alias support, I'd probably go with the GetOrdinal route.
Here is the test in LINQPad form. Feel free to repost with your own method:
void Main()
{
var loopResults = new List<Results>();
var exceptionResults = new List<Results>();
var totalRuns = 10000;
for (var colCount = 1; colCount < 20; colCount++)
{
using (var conn = new SqlConnection(#"Data Source=(localdb)\MSSQLLocalDb;Initial Catalog=master;Integrated Security=True;"))
{
conn.Open();
//create a dummy table where we can control the total columns
var columns = String.Join(",",
(new int[colCount]).Select((item, i) => $"'{i}' as col{i}")
);
var sql = $"select {columns} into #dummyTable";
var cmd = new SqlCommand(sql,conn);
cmd.ExecuteNonQuery();
var cmd2 = new SqlCommand("select * from #dummyTable", conn);
var reader = cmd2.ExecuteReader();
reader.Read();
Func<Func<IDataRecord, String, Boolean>, List<Results>> test = funcToTest =>
{
var results = new List<Results>();
Random r = new Random();
for (var faultRate = 0.1; faultRate <= 0.5; faultRate += 0.1)
{
Stopwatch stopwatch = new Stopwatch();
stopwatch.Start();
var faultCount=0;
for (var testRun = 0; testRun < totalRuns; testRun++)
{
if (r.NextDouble() <= faultRate)
{
faultCount++;
if(funcToTest(reader, "colDNE"))
throw new ApplicationException("Should have thrown false");
}
else
{
for (var col = 0; col < colCount; col++)
{
if(!funcToTest(reader, $"col{col}"))
throw new ApplicationException("Should have thrown true");
}
}
}
stopwatch.Stop();
results.Add(new UserQuery.Results{
ColumnCount = colCount,
TargetNotFoundRate = faultRate,
NotFoundRate = faultCount * 1.0f / totalRuns,
TotalTime=stopwatch.Elapsed
});
}
return results;
};
loopResults.AddRange(test(HasColumnLoop));
exceptionResults.AddRange(test(HasColumnException));
}
}
"Loop".Dump();
loopResults.Dump();
"Exception".Dump();
exceptionResults.Dump();
var combinedResults = loopResults.Join(exceptionResults,l => l.ResultKey, e=> e.ResultKey, (l, e) => new{ResultKey = l.ResultKey, LoopResult=l.TotalTime, ExceptionResult=e.TotalTime});
combinedResults.Dump();
combinedResults
.Chart(r => r.ResultKey, r => r.LoopResult.Milliseconds * 1.0 / totalRuns, LINQPad.Util.SeriesType.Line)
.AddYSeries(r => r.ExceptionResult.Milliseconds * 1.0 / totalRuns, LINQPad.Util.SeriesType.Line)
.Dump();
}
public static bool HasColumnLoop(IDataRecord dr, string columnName)
{
for (int i = 0; i < dr.FieldCount; i++)
{
if (dr.GetName(i).Equals(columnName, StringComparison.InvariantCultureIgnoreCase))
return true;
}
return false;
}
public static bool HasColumnException(IDataRecord r, string columnName)
{
try
{
return r.GetOrdinal(columnName) >= 0;
}
catch (IndexOutOfRangeException)
{
return false;
}
}
public class Results
{
public double NotFoundRate { get; set; }
public double TargetNotFoundRate { get; set; }
public int ColumnCount { get; set; }
public double ResultKey {get => ColumnCount + TargetNotFoundRate;}
public TimeSpan TotalTime { get; set; }
}

Hashtable ht = new Hashtable();
Hashtable CreateColumnHash(SqlDataReader dr)
{
ht = new Hashtable();
for (int i = 0; i < dr.FieldCount; i++)
{
ht.Add(dr.GetName(i), dr.GetName(i));
}
return ht;
}
bool ValidateColumn(string ColumnName)
{
return ht.Contains(ColumnName);
}

Here is a one-liner LINQ version of the accepted answer:
Enumerable.Range(0, reader.FieldCount).Any(i => reader.GetName(i) == "COLUMN_NAME_GOES_HERE")

Here is the solution from Jasmine in one line... (one more, though simple!):
reader.GetSchemaTable().Select("ColumnName='MyCol'").Length > 0;

To keep your code robust and clean, use a single extension function, like this:
Public Module Extensions
<Extension()>
Public Function HasColumn(r As SqlDataReader, columnName As String) As Boolean
Return If(String.IsNullOrEmpty(columnName) OrElse r.FieldCount = 0, False, Enumerable.Range(0, r.FieldCount).Select(Function(i) r.GetName(i)).Contains(columnName, StringComparer.OrdinalIgnoreCase))
End Function
End Module

This code corrects the issues that Levitikon had with their code:
(adapted from: [1]: http://msdn.microsoft.com/en-us/library/system.data.datatablereader.getschematable.aspx)
public List<string> GetColumnNames(SqlDataReader r)
{
List<string> ColumnNames = new List<string>();
DataTable schemaTable = r.GetSchemaTable();
DataRow row = schemaTable.Rows[0];
foreach (DataColumn col in schemaTable.Columns)
{
if (col.ColumnName == "ColumnName")
{
ColumnNames.Add(row[col.Ordinal].ToString());
break;
}
}
return ColumnNames;
}
The reason for getting all of those useless column names and not the name of the column from your table...
Is because your are getting the name of schema column (i.e. the column names for the Schema table)
NOTE: this seems to only return the name of the first column...
EDIT: corrected code that returns the name of all columns, but you cannot use a SqlDataReader to do it
public List<string> ExecuteColumnNamesReader(string command, List<SqlParameter> Params)
{
List<string> ColumnNames = new List<string>();
SqlDataAdapter da = new SqlDataAdapter();
string connection = ""; // your sql connection string
SqlCommand sqlComm = new SqlCommand(command, connection);
foreach (SqlParameter p in Params) { sqlComm.Parameters.Add(p); }
da.SelectCommand = sqlComm;
DataTable dt = new DataTable();
da.Fill(dt);
DataRow row = dt.Rows[0];
for (int ordinal = 0; ordinal < dt.Columns.Count; ordinal++)
{
string column_name = dt.Columns[ordinal].ColumnName;
ColumnNames.Add(column_name);
}
return ColumnNames; // you can then call .Contains("name") on the returned collection
}

Neither did I get GetSchemaTable to work, until I found this way.
Basically I do this:
Dim myView As DataView = dr.GetSchemaTable().DefaultView
myView.RowFilter = "ColumnName = 'ColumnToBeChecked'"
If myView.Count > 0 AndAlso dr.GetOrdinal("ColumnToBeChecked") <> -1 Then
obj.ColumnToBeChecked = ColumnFromDb(dr, "ColumnToBeChecked")
End If

public static bool DataViewColumnExists(DataView dv, string columnName)
{
return DataTableColumnExists(dv.Table, columnName);
}
public static bool DataTableColumnExists(DataTable dt, string columnName)
{
string DebugTrace = "Utils::DataTableColumnExists(" + dt.ToString() + ")";
try
{
return dt.Columns.Contains(columnName);
}
catch (Exception ex)
{
throw new MyExceptionHandler(ex, DebugTrace);
}
}
Columns.Contains is case-insensitive btw.

My data access class needs to be backward compatible, so I might be trying to access a column in a release where it doesn't exist in the database yet. We have some rather large data sets being returned so I'm not a big fan of an extension method that has to iterate the DataReader column collection for each property.
I have a utility class that creates a private list of columns and then has a generic method that attempts to resolve a value based on a column name and output parameter type.
private List<string> _lstString;
public void GetValueByParameter<T>(IDataReader dr, string parameterName, out T returnValue)
{
returnValue = default(T);
if (!_lstString.Contains(parameterName))
{
Logger.Instance.LogVerbose(this, "missing parameter: " + parameterName);
return;
}
try
{
if (dr[parameterName] != null && [parameterName] != DBNull.Value)
returnValue = (T)dr[parameterName];
}
catch (Exception ex)
{
Logger.Instance.LogException(this, ex);
}
}
/// <summary>
/// Reset the global list of columns to reflect the fields in the IDataReader
/// </summary>
/// <param name="dr">The IDataReader being acted upon</param>
/// <param name="NextResult">Advances IDataReader to next result</param>
public void ResetSchemaTable(IDataReader dr, bool nextResult)
{
if (nextResult)
dr.NextResult();
_lstString = new List<string>();
using (DataTable dataTableSchema = dr.GetSchemaTable())
{
if (dataTableSchema != null)
{
foreach (DataRow row in dataTableSchema.Rows)
{
_lstString.Add(row[dataTableSchema.Columns["ColumnName"]].ToString());
}
}
}
}
Then I can just call my code like so
using (var dr = ExecuteReader(databaseCommand))
{
int? outInt;
string outString;
Utility.ResetSchemaTable(dr, false);
while (dr.Read())
{
Utility.GetValueByParameter(dr, "SomeColumn", out outInt);
if (outInt.HasValue) myIntField = outInt.Value;
}
Utility.ResetSchemaTable(dr, true);
while (dr.Read())
{
Utility.GetValueByParameter(dr, "AnotherColumn", out outString);
if (!string.IsNullOrEmpty(outString)) myIntField = outString;
}
}

The key to the whole problem is here:
if (-1 == index) {
throw ADP.IndexOutOfRange(fieldName);
}
If the referenced three lines (currently lines 72, 73, and 74) are taken out, then you can easily check for -1 in order to determine if the column doesn't exist.
The only way around this while ensuring native performance is to use a Reflection based implementation, like the following:
Usings:
using System;
using System.Data;
using System.Reflection;
using System.Data.SqlClient;
using System.Linq;
using System.Web.Compilation; // I'm not sure what the .NET Core equivalent to BuildManager.cs
The Reflection based extension method:
/// Gets the column ordinal, given the name of the column.
/// </summary>
/// <param name="reader"></param>
/// <param name="name">The name of the column.</param>
/// <returns> The zero-based column ordinal. -1 if the column does not exist.</returns>
public static int GetOrdinalSoft(this SqlDataReader reader, string name)
{
try
{
// Note that "Statistics" will not be accounted for in this implemenation
// If you have SqlConnection.StatisticsEnabled set to true (the default is false), you probably don't want to use this method
// All of the following logic is inspired by the actual implementation of the framework:
// https://referencesource.microsoft.com/#System.Data/fx/src/data/System/Data/SqlClient/SqlDataReader.cs,d66096b6f57cac74
if (name == null)
throw new ArgumentNullException("fieldName");
Type sqlDataReaderType = typeof(SqlDataReader);
object fieldNameLookup = sqlDataReaderType.GetField("_fieldNameLookup", BindingFlags.NonPublic | BindingFlags.Instance).GetValue(reader);
Type fieldNameLookupType;
if (fieldNameLookup == null)
{
MethodInfo checkMetaDataIsReady = sqlDataReaderType.GetRuntimeMethods().First(x => x.Name == "CheckMetaDataIsReady" && x.GetParameters().Length == 0);
checkMetaDataIsReady.Invoke(reader, null);
fieldNameLookupType = BuildManager.GetType("System.Data.ProviderBase.FieldNameLookup", true, false);
ConstructorInfo ctor = fieldNameLookupType.GetConstructor(new[] { typeof(SqlDataReader), typeof(int) });
fieldNameLookup = ctor.Invoke(new object[] { reader, sqlDataReaderType.GetField("_defaultLCID", BindingFlags.NonPublic | BindingFlags.Instance).GetValue(reader) });
}
else
fieldNameLookupType = fieldNameLookup.GetType();
MethodInfo indexOf = fieldNameLookupType.GetMethod("IndexOf", BindingFlags.Public | BindingFlags.Instance, null, new Type[] { typeof(string) }, null);
return (int)indexOf.Invoke(fieldNameLookup, new object[] { name });
}
catch
{
// .NET Implemenation might have changed, revert back to the classic solution.
if (reader.FieldCount > 11) // Performance observation by b_levitt
{
try
{
return reader.GetOrdinal(name);
}
catch
{
return -1;
}
}
else
{
var exists = Enumerable.Range(0, reader.FieldCount).Any(i => string.Equals(reader.GetName(i), name, StringComparison.OrdinalIgnoreCase));
if (exists)
return reader.GetOrdinal(name);
else
return -1;
}
}
}

In your particular situation (all procedures has the same columns except one which has an additional one column), it will be better and faster to check the reader's FieldCount property to distinguish between them.
const int NormalColCount = .....
if(reader.FieldCount > NormalColCount)
{
// Do something special
}
You can also (for performance reasons) mix this solution with the solution iterating solution.

I would recommend using try{} catch{} for this simple issue. However, I would not recommend handling exception in catch.
try
{
if (string.IsNullOrEmpty(reader["Name"].ToString()))
{
name = reader["Name"].ToString();
}
}
catch
{
//Do nothing
}

This is a pretty old thread, but I wanted to provide my two cents.
The challenge with most of the proposed solutions is that it requires you to enumerate over all fields every time for every row for every column you're checking.
Others are using the GetSchemaTable method which is not globally supported.
Personally, I have no issue with throwing and catching exceptions to check if a field exists. In fact, I think it's probably the most straightforward solution from a programming perspective and the easiest to debug and create an extension for. I've noticed no negative performance hits on swallowing exceptions except where there is some other transaction involved or weird rollback logic.
Implementation using a try-catch block
using System;
using System.Collections.Generic;
using System.Data.SqlClient;
public class MyModel {
public int ID { get; set; }
public int UnknownColumn { get; set; }
}
public IEnumerable<MyModel> ReadData(SqlCommand command) {
using (SqlDataReader reader = command.ExecuteReader()) {
try {
while (reader.Read()) {
// init the row
MyModel row = new MyModel();
// bind the fields
row.ID = reader.IfDBNull("ID", row.ID);
row.UnknownColumn = reader.IfDBNull("UnknownColumn", row.UnknownColumn);
// return the row and move forward
yield return row;
}
} finally {
// technically the disposer should handle this for you
if (!reader.IsClosed) reader.Close();
}
}
}
// I use a variant of this class everywhere I go to help simplify data binding
public static class IDataReaderExtensions {
// clearly separate name to ensure I don't accidentally use the wrong method
public static T IfDBNull<T>(this IDataReader reader, string name, T defaultValue) {
T value;
try {
// attempt to read the value
// will throw IndexOutOfRangeException if not available
object objValue = reader[name];
// the value returned from SQL is NULL
if (Convert.IsDBNull(objValue)) {
// use the default value
objValue = defaultValue;
}
else if (typeof(T) == typeof(char)) {
// chars are returned from SQL as strings
string strValue = Convert.ToString(objValue);
if (strValue.Length > 0) objValue = strValue[0];
else objValue = defaultValue;
}
value = (T)objValue;
} catch (IndexOutOfRangeException) {
// field does not exist
value = #defaultValue;
} catch (InvalidCastException, ex) {
// The type we are attempting to bind to is not the same as the type returned from the database
// Personally, I want to know the field name that has the problem
throw new InvalidCastException(name, ex);
}
return value;
}
// clearly separate name to ensure I don't accidentally use the wrong method
// just overloads the other method so I don't need to pass in a default
public static T IfDBNull<T>(this IDataReader reader, string name) {
return IfDBNull<T>(reader, name, default(T));
}
}
If you want to avoid exception handling, I'd recommend saving your results to a HashSet<string> when you initialize your reader, then checking back to it for the columns you want. Alternatively for a micro-optimization, you can implement your columns as a Dictionary<string, int> to prevent a duplicate resolution from Name to ordinal by the SqlDataReader object.
Implementation using HashSet<string>
using System;
using System.Collections.Generic;
using System.Data.SqlClient;
public class MyModel {
public int ID { get; set; }
public int UnknownColumn { get; set; }
}
public IEnumerable<MyModel> ReadData(SqlCommand command) {
using (SqlDataReader reader = command.ExecuteReader()) {
try {
// first read
if (reader.Read()) {
// use whatever *IgnoreCase comparer that you're comfortable with
HashSet<string> columns = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
// init the columns HashSet<string, int>
for (int i = 0; i < reader.FieldCount; i++) {
string fieldName = reader.GetName(i);
columns.Add(fieldName);
}
// implemented as a do/while since we already read the first row
do {
// init a new instance of your class
MyModel row = new MyModel();
// check if column exists
if (columns.Contains("ID") &&
// ensure the value is not DBNull
!Convert.IsDBNull(reader["ID"])) {
// bind value
row.ID = (int)reader["ID"];
}
// check if column exists
if (columns.Contains("UnknownColumn") &&
// ensure the value is not DBNull
!Convert.IsDBNull(reader["UnknownColumn"])) {
// bind value
row.UnknownColumn = (int)reader["UnknownColumn"];
}
// return the row and move forward
yield return row;
} while (reader.Read());
}
} finally {
// technically the disposer should handle this for you
if (!reader.IsClosed) reader.Close();
}
}
}
Implementation using Dictionary<string, int>
using System;
using System.Collections.Generic;
using System.Data.SqlClient;
public class MyModel {
public int ID { get; set; }
public int UnknownColumn { get; set; }
}
public IEnumerable<MyModel> ReadData(SqlCommand command) {
using (SqlDataReader reader = command.ExecuteReader()) {
try {
// first read
if (reader.Read()) {
// use whatever *IgnoreCase comparer that you're comfortable with
Dictionary<string, int> columns = new Dictionary<string, int>(StringComparer.OrdinalIgnoreCase);
// init the columns Dictionary<string, int>
for (int i = 0; i < reader.FieldCount; i++) {
string fieldName = reader.GetName(i);
columns[fieldName] = i;
}
// implemented as a do/while since we already read the first row
do {
// init a new instance of your class
MyModel row = new MyModel();
// stores the resolved ordinal from your dictionary
int ordinal;
// check if column exists
if (columns.TryGetValue("ID", out ordinal) &&
// ensure the value is not DBNull
!Convert.IsDBNull(reader[ordinal])) {
// bind value
row.ID = (int)reader[ordinal];
}
// check if column exists
if (columns.TryGetValue("UnknownColumn", out ordinal) &&
// ensure the value is not DBNull
!Convert.IsDBNull(reader[ordinal])) {
// bind value
row.UnknownColumn = (int)reader[ordinal];
}
// return the row and move forward
yield return row;
} while (reader.Read());
}
} finally {
// technically the disposer should handle this for you
if (!reader.IsClosed) reader.Close();
}
}
}

You can also call GetSchemaTable() on your DataReader if you want the list of columns and you don't want to have to get an exception...

Although there is no publicly exposed method, a method does exist in the internal class System.Data.ProviderBase.FieldNameLookup which SqlDataReader relies on.
In order to access it and get native performance, you must use the ILGenerator to create a method at runtime. The following code will give you direct access to int IndexOf(string fieldName) in the System.Data.ProviderBase.FieldNameLookup class as well as perform the book keeping that SqlDataReader.GetOrdinal()does so that there is no side effect. The generated code mirrors the existing SqlDataReader.GetOrdinal() except that it calls FieldNameLookup.IndexOf() instead of FieldNameLookup.GetOrdinal(). The GetOrdinal() method calls to the IndexOf() function and throws an exception if -1 is returned, so we bypass that behavior.
using System;
using System.Data;
using System.Data.SqlClient;
using System.Reflection;
using System.Reflection.Emit;
public static class SqlDataReaderExtensions {
private delegate int IndexOfDelegate(SqlDataReader reader, string name);
private static IndexOfDelegate IndexOf;
public static int GetColumnIndex(this SqlDataReader reader, string name) {
return name == null ? -1 : IndexOf(reader, name);
}
public static bool ContainsColumn(this SqlDataReader reader, string name) {
return name != null && IndexOf(reader, name) >= 0;
}
static SqlDataReaderExtensions() {
Type typeSqlDataReader = typeof(SqlDataReader);
Type typeSqlStatistics = typeSqlDataReader.Assembly.GetType("System.Data.SqlClient.SqlStatistics", true);
Type typeFieldNameLookup = typeSqlDataReader.Assembly.GetType("System.Data.ProviderBase.FieldNameLookup", true);
BindingFlags staticflags = BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.IgnoreCase | BindingFlags.Static;
BindingFlags instflags = BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.IgnoreCase | BindingFlags.Instance;
DynamicMethod dynmethod = new DynamicMethod("SqlDataReader_IndexOf", typeof(int), new Type[2]{ typeSqlDataReader, typeof(string) }, true);
ILGenerator gen = dynmethod.GetILGenerator();
gen.DeclareLocal(typeSqlStatistics);
gen.DeclareLocal(typeof(int));
// SqlStatistics statistics = (SqlStatistics) null;
gen.Emit(OpCodes.Ldnull);
gen.Emit(OpCodes.Stloc_0);
// try {
gen.BeginExceptionBlock();
// statistics = SqlStatistics.StartTimer(this.Statistics);
gen.Emit(OpCodes.Ldarg_0); //this
gen.Emit(OpCodes.Call, typeSqlDataReader.GetProperty("Statistics", instflags | BindingFlags.GetProperty, null, typeSqlStatistics, Type.EmptyTypes, null).GetMethod);
gen.Emit(OpCodes.Call, typeSqlStatistics.GetMethod("StartTimer", staticflags | BindingFlags.InvokeMethod, null, new Type[] { typeSqlStatistics }, null));
gen.Emit(OpCodes.Stloc_0); //statistics
// if(this._fieldNameLookup == null) {
Label branchTarget = gen.DefineLabel();
gen.Emit(OpCodes.Ldarg_0); //this
gen.Emit(OpCodes.Ldfld, typeSqlDataReader.GetField("_fieldNameLookup", instflags | BindingFlags.GetField));
gen.Emit(OpCodes.Brtrue_S, branchTarget);
// this.CheckMetaDataIsReady();
gen.Emit(OpCodes.Ldarg_0); //this
gen.Emit(OpCodes.Call, typeSqlDataReader.GetMethod("CheckMetaDataIsReady", instflags | BindingFlags.InvokeMethod, null, Type.EmptyTypes, null));
// this._fieldNameLookup = new FieldNameLookup((IDataRecord)this, this._defaultLCID);
gen.Emit(OpCodes.Ldarg_0); //this
gen.Emit(OpCodes.Ldarg_0); //this
gen.Emit(OpCodes.Ldarg_0); //this
gen.Emit(OpCodes.Ldfld, typeSqlDataReader.GetField("_defaultLCID", instflags | BindingFlags.GetField));
gen.Emit(OpCodes.Newobj, typeFieldNameLookup.GetConstructor(instflags, null, new Type[] { typeof(IDataReader), typeof(int) }, null));
gen.Emit(OpCodes.Stfld, typeSqlDataReader.GetField("_fieldNameLookup", instflags | BindingFlags.SetField));
// }
gen.MarkLabel(branchTarget);
gen.Emit(OpCodes.Ldarg_0); //this
gen.Emit(OpCodes.Ldfld, typeSqlDataReader.GetField("_fieldNameLookup", instflags | BindingFlags.GetField));
gen.Emit(OpCodes.Ldarg_1); //name
gen.Emit(OpCodes.Call, typeFieldNameLookup.GetMethod("IndexOf", instflags | BindingFlags.InvokeMethod, null, new Type[] { typeof(string) }, null));
gen.Emit(OpCodes.Stloc_1); //int output
Label leaveProtectedRegion = gen.DefineLabel();
gen.Emit(OpCodes.Leave_S, leaveProtectedRegion);
// } finally {
gen.BeginFaultBlock();
// SqlStatistics.StopTimer(statistics);
gen.Emit(OpCodes.Ldloc_0); //statistics
gen.Emit(OpCodes.Call, typeSqlStatistics.GetMethod("StopTimer", staticflags | BindingFlags.InvokeMethod, null, new Type[] { typeSqlStatistics }, null));
// }
gen.EndExceptionBlock();
gen.MarkLabel(leaveProtectedRegion);
gen.Emit(OpCodes.Ldloc_1);
gen.Emit(OpCodes.Ret);
IndexOf = (IndexOfDelegate)dynmethod.CreateDelegate(typeof(IndexOfDelegate));
}
}

Use:
if (dr.GetSchemaTable().Columns.Contains("accounttype"))
do something
else
do something
It probably would not be as efficient in a loop.

This works to me:
public static class DataRecordExtensions
{
public static bool HasColumn(IDataReader dataReader, string columnName)
{
dataReader.GetSchemaTable().DefaultView.RowFilter = $"ColumnName= '{columnName}'";
return (dataReader.GetSchemaTable().DefaultView.Count > 0);
}
}

Use:
if(Enumerable.Range(0,reader.FieldCount).Select(reader.GetName).Contains("columName"))
{
employee.EmployeeId= Utility.ConvertReaderToLong(reader["EmployeeId"]);
}
You can get more details from Can you get the column names from a SqlDataReader?.

List from datagridview gives System.InvalidCastException

I have a class called GetKoord in which I want to read a datagridview from and put it into a list. I've made a class vertEl which I made because I got an error with recursive stackoverflowexception at first.
The problem with this code comes when I'm in my public partial class try to make a list from vertElementerDgv. The loop in my class to add list-items doesn't work properly and gives the exception.
I appreciate all the help I can get! If some info is missing tell me and I'll provide it as good as I can.
GetKoord getKoord = new GetKoord();
//Opens the file dialog and assigns file path to Textbox
OpenFileDialog browseButton = new OpenFileDialog();
private void browse_Click(object sender, EventArgs e)
{
DGV = nylpDgv;
browseButton.Filter = "Excel Files |*.xlsx;*.xls;*.xlsm;*.csv";
if (browseButton.ShowDialog() == DialogResult.OK)
{
ExcelPath.Text = browseButton.FileName;
fileExcel = ExcelPath.Text;
//SetAttributeValue(ExcelPath, fileExcel);
//nylp();
/*
////IMPORTERER 10TAB-DATA FRA EXCEL TIL DATAGRIDVIEW////
tenTabLine.fileExcel = fileExcel;
tenTabLine.tenTab(tenTabDgv);
*/
////IMPORTERER NYLPDATA TIL DATAGRIDVIEW////
nylpLine.fileExcel = fileExcel;
nylpLine.nylpData(nylpDgv);
////TAR DATA I NYLPDGV DATAGRIDVIEW OG BEREGNER VERTIKALE ELEMENTER////
vertElementer.vertBueDGV(nylpDgv, vertElementerDgv);
////HENTER KOORDINATER////
var TEST = getKoord.vertList(vertElementerDgv); //THIS IS CAUSING ERROR
MessageBox.Show(TEST[5].elNr.ToString());
}
else return;
}
The GetKoord class and vertEl class are as followed:
class GetKoord
{
List<vertEl> vertTEST = new List<vertEl>();
public List<vertEl> vertList(DataGridView VertElementer)
{
for (int i = 0; i<VertElementer.Rows.Count - 1; i++)
{
vertTEST.Add(new vertEl
{
elNr = (int)VertElementer.Rows[i].Cells[0].Value,
p1 = (double)VertElementer.Rows[i].Cells[1].Value,
p2 = (double)VertElementer.Rows[i].Cells[2].Value,
z1 = (double)VertElementer.Rows[i].Cells[3].Value,
z2 = (double)VertElementer.Rows[i].Cells[4].Value,
heln1 = (double)VertElementer.Rows[i].Cells[5].Value,
heln2 = (double)VertElementer.Rows[i].Cells[6].Value
});
}
return vertTEST;
}
/*
public double zKoord(double pNr)
{
// zKoord() =
return zKoord(pNr);
}
*/
}
class vertEl
{
private int _elNr;
private double _p1;
private double _p2;
private double _z1;
private double _z2;
private double _nylpRad;
private double _heln1;
private double _heln2;
public int elNr
{
get { return _elNr; }
set { _elNr = value; }
}
public double p1
{
get { return _p1; }
set { _p1 = value; }
}
public double p2
{
get { return _p2; }
set { _p2 = value; }
}
public double z1
{
get { return _z1; }
set { _z1 = value; }
}
public double z2
{
get { return _z2; }
set { _z2 = value; }
}
public double nylpRad
{
get { return _nylpRad; }
set { _nylpRad = value; }
}
public double heln1
{
get { return _heln1; }
set { _heln1 = value; }
}
public double heln2
{
get { return _heln2; }
set { _heln2 = value; }
}
}

The data types of Excel are not always the one you are expecting and you are casting into. You have to convert the values by your own:
vertTEST.Add(new vertEl
{
elNr = Convert.ToInt32(VertElementer.Rows[i].Cells[0].Value),
p1 = Convert.ToDouble(VertElementer.Rows[i].Cells[1].Value),
p2 = Convert.ToDouble(VertElementer.Rows[i].Cells[2].Value),
z1 = Convert.ToDouble(VertElementer.Rows[i].Cells[3].Value),
z2 = Convert.ToDouble(VertElementer.Rows[i].Cells[4].Value),
heln1 = Convert.ToDouble(VertElementer.Rows[i].Cells[5].Value),
heln2 = Convert.ToDouble(VertElementer.Rows[i].Cells[6].Value)
});

From what your comments and code show, I am confident you are getting this error from one of the Value conversions. Example, if one of the cells in the DataGridView is empty and you try to cast this “Empty” value to a double you will get this error.
Checking for these null values and bad number formats should be done either way, but especially when trying to cast a string to a number. There is always the possibility that the string is not a number. Assuming the values are all correct the other possibility is the added row in a DataGridView. So just taking a guess here, I would suggest two ways to help find where this error is coming from. First, check for null values and use a tryParse to help weed out bad int/double values. Also use a foreach to loop through the rows.
First create a new List to hold the vertEl objects. The tempInt and tempDouble variables are used to hold each tryParse result. You may have seen the tryParse used in an if statement like below
Int result = 0;
If (int.tryParse(someString, out result) {
// here the parse was successful – result is a valid number
}
else {
// either null or bad number format – result is still valid and is set to zero.
}
This is one way you could figure out where your error is coming from by adding a check for a null cell or the value in the cell is a bad number format. The code below simply ignores bad values and sets a default value of zero (0) for these bad values. The tryParse will return false if the string is null or is an invalid number format. In this case we really do not care which one; we will simply set this value to zero (0) which is what the tryParse returns in its out variable when the parse fails. So checking if it fails or succeeds is unnecessary. If it fails, the returned number will be zero. Hope this helps.
private List<vertEl> GetVertList() {
List<vertEl> vertTEST = new List<vertEl>();
int tempInt = 0;
double tempDouble = 0.0;
foreach (DataGridViewRow row in VertElementer.Rows) {
if (!row.IsNewRow) {
vertEl vert1 = new vertEl();
int.TryParse(row.Cells[0].Value.ToString(), out tempInt);
vert1.elNr = tempInt;
double.TryParse(row.Cells[1].Value.ToString(), out tempDouble);
vert1.p1 = tempDouble;
double.TryParse(row.Cells[2].Value.ToString(), out tempDouble);
vert1.p2 = tempDouble;
double.TryParse(row.Cells[3].Value.ToString(), out tempDouble);
vert1.z1 = tempDouble;
double.TryParse(row.Cells[4].Value.ToString(), out tempDouble);
vert1.z2 = tempDouble;
double.TryParse(row.Cells[5].Value.ToString(), out tempDouble);
vert1.heln1 = tempDouble;
double.TryParse(row.Cells[6].Value.ToString(), out tempDouble);
vert1.heln2 = tempDouble;
vertTEST.Add(vert1);
}
}
return vertTEST;
}

CSV-file values to List<List>

I have a CSV file that I want some values from. One problem is that I don't know how many columns the file has. The number can be different every time I get a new CSV file. It will always have columns and rows with values. I will get it from a normal excel-file.
I want the method to return a List<List>.
ListA(FirstName, LastName, PhoneNumber... and so on) here I don't know how many items ListA will have. It can be different every time.
Inside ListA I want lists of persons like this:
ListA[FirstName] = List1(Zlatan, Lionel, Anders.....)
ListA[LastName] = List2(Ibrahimovic, Messi, Svensson.....) .. and so on.

You could create a class Person
class person {
private string FirstName;
private string LastName;
// others
}
Open the File and split each row in the file with the String.Split()-Method then convert each value and create Objects, which you can add to a List.
List<Person> persons = new List<Person>();
persons.Add(personFromFile);
Thats a pretty short solution but it works
Edit: Variable Fields per Row
If thats the case you could use a List<string[]> stringArraylist; and then add the results of the String.Split()-Method to it.
List<string[]> stringArraylist;
stringArraylist = new List<string[]>();
stringArraylist.Add("Andrew;Pearson;...;lololo;".Split(';'));
Is that more of what you wanted?

There are a lot of questions on SO that deal with parsing CSV files. See here for one: Reading CSV files in C#. I am fairly certain there are some solutions built in to .NET, though I can't recall what they are at the moment. (#ZoharPeled suggested TextFieldParser)
Most of the parsing solutions with give you a collection of rows where each item is a collection of columns. So assuming you have something like a IEnumerable<IList<string>>, you could create a class and use LINQ queries to get what you need:
public class CSVColumns
{
public IEnumerable<IList<string>> CSVContents { get; private set; }
public CSVColumns(IEnumerable<IList<string>> csvcontents)
{
this.CSVContents = csvcontents;
}
public List<string> FirstNames
{
get { return GetColumn("FirstName"); }
}
public List<string> LastNames
{
get { return GetColumn("LastName"); }
}
/// <summary>
/// Gets a collection of the column data based on the name of the column
/// from the header row.
/// </summary>
public List<string> GetColumn(string columnname)
{
//Get the index of the column with the name
var firstrow = CSVContents.ElementAtOrDefault(0);
if (firstrow != null)
{
int index = -1;
foreach (string s in firstrow)
{
index++;
if (s == columnname)
{
return GetColumn(index, true);
}
}
}
return new List<string>();
}
/// <summary>
/// Gets all items from a specific column number but skips the
/// header row if needed.
/// </summary>
public List<string> GetColumn(int index, bool hasHeaderRow = true)
{
IEnumerable<IList<string>> columns = CSVContents;
if (hasHeaderRow)
columns = CSVContents.Skip(1);
return columns.Select(list =>
{
try
{
return list[index];
}
catch (IndexOutOfRangeException ex)
{
return "";
}
}
).ToList();
}
}

I finally got a solution and it's working for me. My friend made it so all creed to him. No user here on stackoverflow so I post it instead.
private List<Attributes> LoadCsv()
{
string filename = #"C:\Desktop\demo.csv";
// Get the file's text.
string whole_file = System.IO.File.ReadAllText(filename);
// Split into lines.
whole_file = whole_file.Replace('\n', '\r');
string[] lines = whole_file.Split(new char[] { '\r' },
StringSplitOptions.RemoveEmptyEntries);
// See how many rows and columns there are.
int num_rows = lines.Length;
int num_cols = lines[0].Split(';').Length;
// Allocate the data array.
string[,] values = new string[num_rows, num_cols];
// Load the array.
for (int r = 0; r < num_rows; r++)
{
string[] line_r = lines[r].Split(';');
for (int c = 0; c < num_cols; c++)
{
values[r, c] = line_r[c];
}
}
var attr = new List<Attributes>();
for (var r = 0; r < num_rows; r++)
{
if (r == 0)
{
for (var c = 0; c < num_cols; c++)
{
attr.Add(new Attributes());
attr[c].Name = values[r, c];
attr[c].Value = new List<String>();
}
}
else
{
for (var b = 0; b < num_cols; b++)
{
var input = values[r, b];
attr[b].Value.Add(input);
}
}
}
// Return the values.
return attr;
}

Excel ExcelDNA C# / Try to copy Bloomberg BDH() behavior (writing Array after a web request)

I want to copy Bloomberg BDH behavior.
BDH makes a web request and write an array (but doesn't return an array style). During this web request, the function returns "#N/A Requesting".
When the web request finished, the BDH() function writes the array result in the worksheet.
For example, in ExcelDNA, I succeed to write in the worksheet with a thread.
The result if you use the code below in a DNA file, the result of
=WriteArray(2;2)
will be
Line 1 > #N/A Requesting Data (0,1)
Line 2 > (1,0) (1,1)
The last issue is to replace #N/A Requesting Data with the value and copy the formula.
When you uncomment //xlActiveCellType.InvokeMember("FormulaR1C1Local", you are near the result but you don't have the right behavior
File .dna
<DnaLibrary Language="CS" RuntimeVersion="v4.0">
<![CDATA[
using System;
using System.Collections.Generic;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Threading;
using ExcelDna.Integration;
public static class WriteForXL
{
public static object[,] MakeArray(int rows, int columns)
{
if (rows == 0 && columns == 0)
{
rows = 1;
columns = 1;
}
object[,] result = new string[rows, columns];
for (int i = 0; i < rows; i++)
{
for (int j = 0; j < columns; j++)
{
result[i, j] = string.Format("({0},{1})", i, j);
}
}
return result;
}
public static object WriteArray(int rows, int columns)
{
if (ExcelDnaUtil.IsInFunctionWizard())
return "Waiting for click on wizard ok button to calculate.";
object[,] result = MakeArray(rows, columns);
var xlApp = ExcelDnaUtil.Application;
Type xlAppType = xlApp.GetType();
object caller = xlAppType.InvokeMember("ActiveCell", BindingFlags.GetProperty, null, xlApp, null);
object formula = xlAppType.InvokeMember("FormulaR1C1Local", BindingFlags.GetProperty, null, caller, null);
ObjectForThread q = new ObjectForThread() { xlRef = caller, value = result, FormulaR1C1Local = formula };
Thread t = new Thread(WriteFromThread);
t.Start(q);
return "#N/A Requesting Data";
}
private static void WriteFromThread(Object o)
{
ObjectForThread q = (ObjectForThread) o;
Type xlActiveCellType = q.xlRef.GetType();
try
{
for (int i = 0; i < q.value.GetLength(0); i++)
{
for (int j = 0; j < q.value.GetLength(1); j++)
{
if (i == 0 && j == 0)
continue;
Object cellBelow = xlActiveCellType.InvokeMember("Offset", BindingFlags.GetProperty, null, q.xlRef, new object[] { i, j });
xlActiveCellType.InvokeMember("Value", BindingFlags.SetProperty, null, cellBelow, new[] { Type.Missing, q.value[i, j] });
}
}
}
catch(Exception e)
{
}
finally
{
//xlActiveCellType.InvokeMember("Value", BindingFlags.SetProperty, null, q.xlRef, new[] { Type.Missing, q.value[0, 0] });
//xlActiveCellType.InvokeMember("FormulaR1C1Local", BindingFlags.SetProperty, null, q.xlRef, new [] { q.FormulaR1C1Local });
}
}
public class ObjectForThread
{
public object xlRef { get; set; }
public object[,] value { get; set; }
public object FormulaR1C1Local { get; set; }
}
}
]]>
</DnaLibrary>
#To Govert
BDH has become a standard in finance industry. People do not know how to manipulate an array (even the Ctrl+Shift+Enter).
BDH is the function that made Bloomberg so popular (to the disadvantage of Reuters).
However I will think of using your method or RTD.
Thanks for all your work in Excel DNA

I presume you have tried the Excel-DNA ArrayResizer sample, which carefully avoids many of the issue you are running into. I'd like to understand what you see as the disadvantages of the array-formula-writing approach.
Now, about your function:
Firstly, you can't safely pass the 'caller' Range COM object to another thread - rather pass a string with the address, and get the COM object from the other thread (using a call to ExcelDnaUtil.Application on the worker thread). Most of the time you'll get lucky, though.
The better way to do this is from the worker thread to get Excel to run a macro on the main thread - by calling Application.Run. The Excel-DNA ArrayResizer sample shows how this can be done.
Secondly, you almost certainly don't want the ActiveCell, but rather Application.Caller. The ActiveCell might well have nothing to do with the cell where the formula is running from.
Next - Excel will recalculate your function every time you set the Formula again - hence putting you in an endless loop when you enable the Formula set in your finally clause. You cannot set both the Value and the Formula for a cell - if a cell has a Formula then Excel will use the formula to calculate the Value. If you set the Value, the Formula gets removed.
It's not clear what you want to actually leave in the [0,0] cell - IIRC Bloomberg modifies the formula there in a way that makes it remember how large a range was written to. You could try to add some parameters to your function that tell your function whether to recalculate or whether to return an actual value as its result.
Finally, you might want to reconsider whether the Bloomberg BDH function is a good example for what you want to do. It breaks the dependency calculation of your sheet, which has implications both for performance and for maintaining consistency of the spreadsheet model.

My issue was :
writing dynamic array
data are retrieved asynchronous via a webservice
After discussing with Govert, I chose to take a result as an array and not to copy Bloomberg functions (write an array but return a single value).
Finally, to solve my issue, I used http://excel-dna.net/2011/01/30/resizing-excel-udf-result-arrays/
and reshape the resize() function.
This code is not RTD.
The code belows works in a .dna file
<DnaLibrary RuntimeVersion="v4.0" Language="C#">
<![CDATA[
using System;
using System.Collections.Generic;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Threading;
using System.ComponentModel;
using ExcelDna.Integration;
public static class ResizeTest
{
public static object[,] MakeArray(int rows, int columns)
{
object[,] result = new string[rows, columns];
for (int i = 0; i < rows; i++)
{
for (int j = 0; j < columns; j++)
{
result[i,j] = string.Format("({0},{1})", i, j);
}
}
return result;
}
public static object MakeArrayAndResize()
{
// Call Resize via Excel - so if the Resize add-in is not part of this code, it should still work.
return XlCall.Excel(XlCall.xlUDF, "Resize", null);
}
}
public class Resizer
{
static Queue<ExcelReference> ResizeJobs = new Queue<ExcelReference>();
static Dictionary<string, object> JobIsDone = new Dictionary<string, object>();
// This function will run in the UDF context.
// Needs extra protection to allow multithreaded use.
public static object Resize(object args)
{
ExcelReference caller = XlCall.Excel(XlCall.xlfCaller) as ExcelReference;
if (caller == null)
return ExcelError.ExcelErrorNA;
if (!JobIsDone.ContainsKey(GetHashcode(caller)))
{
BackgroundWorker(caller);
return ExcelError.ExcelErrorNA;
}
else
{
// Size is already OK - just return result
object[,] array = (object[,])JobIsDone[GetHashcode(caller)];
JobIsDone.Remove(GetHashcode(caller));
return array;
}
}
/// <summary>
/// Simulate WebServiceRequest
/// </summary>
/// <param name="caller"></param>
/// <param name="rows"></param>
/// <param name="columns"></param>
static void BackgroundWorker(ExcelReference caller)
{
BackgroundWorker bw = new BackgroundWorker();
bw.DoWork += (sender, args) =>
{
Thread.Sleep(3000);
};
bw.RunWorkerCompleted += (sender, args) =>
{
// La requete
Random r = new Random();
object[,] array = ResizeTest.MakeArray(r.Next(10), r.Next(10));
JobIsDone[GetHashcode(caller)] = array;
int rows = array.GetLength(0);
int columns = array.GetLength(1);
EnqueueResize(caller, rows, columns);
AsyncRunMacro("DoResizing");
};
bw.RunWorkerAsync();
}
static string GetHashcode(ExcelReference caller)
{
return caller.SheetId + ":L" + caller.RowFirst + "C" + caller.ColumnFirst;
}
static void EnqueueResize(ExcelReference caller, int rows, int columns)
{
ExcelReference target = new ExcelReference(caller.RowFirst, caller.RowFirst + rows - 1, caller.ColumnFirst, caller.ColumnFirst + columns - 1, caller.SheetId);
ResizeJobs.Enqueue(target);
}
public static void DoResizing()
{
while (ResizeJobs.Count > 0)
{
DoResize(ResizeJobs.Dequeue());
}
}
static void DoResize(ExcelReference target)
{
try
{
// Get the current state for reset later
XlCall.Excel(XlCall.xlcEcho, false);
// Get the formula in the first cell of the target
string formula = (string)XlCall.Excel(XlCall.xlfGetCell, 41, target);
ExcelReference firstCell = new ExcelReference(target.RowFirst, target.RowFirst, target.ColumnFirst, target.ColumnFirst, target.SheetId);
bool isFormulaArray = (bool)XlCall.Excel(XlCall.xlfGetCell, 49, target);
if (isFormulaArray)
{
object oldSelectionOnActiveSheet = XlCall.Excel(XlCall.xlfSelection);
object oldActiveCell = XlCall.Excel(XlCall.xlfActiveCell);
// Remember old selection and select the first cell of the target
string firstCellSheet = (string)XlCall.Excel(XlCall.xlSheetNm, firstCell);
XlCall.Excel(XlCall.xlcWorkbookSelect, new object[] {firstCellSheet});
object oldSelectionOnArraySheet = XlCall.Excel(XlCall.xlfSelection);
XlCall.Excel(XlCall.xlcFormulaGoto, firstCell);
// Extend the selection to the whole array and clear
XlCall.Excel(XlCall.xlcSelectSpecial, 6);
ExcelReference oldArray = (ExcelReference)XlCall.Excel(XlCall.xlfSelection);
oldArray.SetValue(ExcelEmpty.Value);
XlCall.Excel(XlCall.xlcSelect, oldSelectionOnArraySheet);
XlCall.Excel(XlCall.xlcFormulaGoto, oldSelectionOnActiveSheet);
}
// Get the formula and convert to R1C1 mode
bool isR1C1Mode = (bool)XlCall.Excel(XlCall.xlfGetWorkspace, 4);
string formulaR1C1 = formula;
if (!isR1C1Mode)
{
// Set the formula into the whole target
formulaR1C1 = (string)XlCall.Excel(XlCall.xlfFormulaConvert, formula, true, false, ExcelMissing.Value, firstCell);
}
// Must be R1C1-style references
object ignoredResult;
XlCall.XlReturn retval = XlCall.TryExcel(XlCall.xlcFormulaArray, out ignoredResult, formulaR1C1, target);
if (retval != XlCall.XlReturn.XlReturnSuccess)
{
// TODO: Consider what to do now!?
// Might have failed due to array in the way.
firstCell.SetValue("'" + formula);
}
}
finally
{
XlCall.Excel(XlCall.xlcEcho, true);
}
}
// Most of this from the newsgroup: http://groups.google.com/group/exceldna/browse_thread/thread/a72c9b9f49523fc9/4577cd6840c7f195
private static readonly TimeSpan BackoffTime = TimeSpan.FromSeconds(1);
static void AsyncRunMacro(string macroName)
{
// Do this on a new thread....
Thread newThread = new Thread( delegate ()
{
while(true)
{
try
{
RunMacro(macroName);
break;
}
catch(COMException cex)
{
if(IsRetry(cex))
{
Thread.Sleep(BackoffTime);
continue;
}
// TODO: Handle unexpected error
return;
}
catch(Exception ex)
{
// TODO: Handle unexpected error
return;
}
}
});
newThread.Start();
}
static void RunMacro(string macroName)
{
object xlApp = null;
try
{
xlApp = ExcelDnaUtil.Application;
xlApp.GetType().InvokeMember("Run", BindingFlags.InvokeMethod, null, xlApp, new object[] {macroName});
}
catch (TargetInvocationException tie)
{
throw tie.InnerException;
}
finally
{
Marshal.ReleaseComObject(xlApp);
}
}
const uint RPC_E_SERVERCALL_RETRYLATER = 0x8001010A;
const uint VBA_E_IGNORE = 0x800AC472;
static bool IsRetry(COMException e)
{
uint errorCode = (uint)e.ErrorCode;
switch(errorCode)
{
case RPC_E_SERVERCALL_RETRYLATER:
case VBA_E_IGNORE:
return true;
default:
return false;
}
}
}
]]>
</DnaLibrary>

I think you need to implemented the request as a RTD server. Normal user defined functions will not update asynchronously.
Then you may hide the call of the RTD server via a user defined function, which can be done via Excel-DNA.

So finally you use Array formula, right? As you said, users are not familiar with array formula, they do not know ctrl+shift+enter. I think array formula is a big problem for them.
For me, I have the same issue. I am trying to build a prototype for it. see
https://github.com/kchen0723/ExcelAsync.git