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get the value of the attributes in C#

this is a very simple question.
such as this code:
if(o == null)
{
o = new { };
}
PropertyInfo[] p1 = o.GetType().GetProperties();
foreach(PropertyInfo pi in p1)
{}
but like this:
ModelA.ModelB.ModelC.ModelD.ModelE
how to get ModelE's value by reflect ModelA

There is a solution explained here:
using a helper method:
public static class ReflectionHelper
{
public static Object GetPropValue(this Object obj, String propName)
{
string[] nameParts = propName.Split('.');
if (nameParts.Length == 1)
{
return obj.GetType().GetProperty(propName).GetValue(obj, null);
}
foreach (String part in nameParts)
{
if (obj == null) { return null; }
Type type = obj.GetType();
PropertyInfo info = type.GetProperty(part);
if (info == null) { return null; }
obj = info.GetValue(obj, null);
}
return obj;
}
}
then the method can be used like this:
ModelA obj = new ModelA { */....*/ };
obj.GetPropValue("modelB.modelC.modelD.modelE");
please note that you should pass the property names to the function not the class names.

using nested function to do it like following:
var testObj = new
{
nameA = "A",
ModelB = new
{
nameB = "B",
ModelC = new
{
NameC = "C",
}
}
};
var result = ParseProperty(testObj, null, "ModelA");
public Dictionary<string, object> ParseProperty(object o, Dictionary<string, object> result, string preFix = null)
{
result = result ?? new Dictionary<string, object>();
if (o == null) return result;
Type t = o.GetType();
//primitive type or value type or string or nested return
if (t.IsPrimitive || t.IsValueType || t.FullName == "System.String" || t.IsNested) return result;
var proerties = o.GetType().GetProperties();
foreach (var property in proerties)
{
var value = property.GetValue(o);
result.Add($"{preFix}.{property.Name}", value);
//nested call
ParseProperty(value, result, $"{preFix}.{property.Name}");
}
return result;
}

I assume these are all anonymous types because otherwise you could just do GetProperties() on the type of ModelE.
So you basically have to next 5 of your loops like
foreach (PropertyInfo pi1 in o1.GetType().GetProperties())
{
if (pi.Name = "ModelB") // or some other criterion
{
o2 = pi1.GetValue(o1);
foreach (PropertyInfo pi2 in o2.GetType().GetProperties())
{
if (pi.Name = "ModelC") // or some other criterion
{
o3 = pi1.GetValue(o2);
// and so on
}
}
}
}

How can I create a generic method to compare two list of any type. The type may be a List of class as well

Following is a class
public class Attribute
{
public string Name { get; set; }
public string Value { get; set; }
}
Following is the code in my main method
{
var test = new List<Attribute>();
test.Add(new Attribute { Name = "Don", Value = "21" });
test.Add(new Attribute { Value = "34", Name = "Karthik" });
var test1 = new List<Attribute>();
test1.Add(new Attribute { Name = "Don", Value = "21" });
test1.Add(new Attribute { Value = "34", Name = "Karthik" });
var obj = new Program();
var areEqual1 = obj.CompareList<List<Attribute>>(test, test1);
}
I have a ComapreList method
public bool CompareList<T>(T firstList, T secondList) where T : class
{
var list1 = firstList as IList<T>;
return true;
}
Now, list1 has null. I know that .net does not allow us to do this. But is there any other way where I can cast this generic list. My purpose is to compare each property value of these two list. I am using reflection to get the property but it works only if I can convert the firstlist/secondlist to something enumerable. if I directly use the name of the class in the IList<> (firstList as IList<Attribute>) it works, but not if I give <T>. Please help.

Just create method parameterized by type of lists items type. Even more, you can create method which compares any type of collections:
public bool CompareSequences<T> (IEnumerable<T> first, IEnumerable<T> second,
Comparer<T> comparer = null)
{
comparer = comparer ?? Comparer<T>.Default;
if (first == null)
throw new ArgumentNullException(nameof(first));
if (second == null)
throw new ArgumentNullException(nameof(second));
var firstIterator = first.GetEnumerator();
var secondIterator = second.GetEnumerator();
while(true)
{
bool firstHasItem = firstIterator.MoveNext();
bool secondHasItem = secondIterator.MoveNext();
if (firstHasItem != secondHasItem)
return false;
if (!firstHasItem && !secondHasItem)
return true;
if (comparer.Compare(firstIterator.Current, secondIterator.Current) != 0)
return false;
}
}
If collection items are primitive types, you can use default comparer. But if collections contain custom items, you need either IComparable to be implemented by collection items type:
public class Attribute : IComparable<Attribute>
{
public string Name { get; set; }
public string Value { get; set; }
public int CompareTo (Attribute other)
{
int result = Name.CompareTo(other.Name);
if (result == 0)
return Value.CompareTo(other.Value);
return result;
}
}
Or you can create and pass comparer instance. You can create comparer which is using reflection to compare fields/properties of some type. But it's not as simple as you might think - properties can be complex type or collections.
Usage:
var areEqual1 = obj.CompareSequences(test, test1);
If you don't need to compare objects with complex structure (which have inner collections and other custom objects) then you can use comparer like this one:
public class SimplePropertiesComparer<T> : Comparer<T>
{
public override int Compare (T x, T y)
{
Type type = typeof(T);
var flags = BindingFlags.GetProperty | BindingFlags.Public | BindingFlags.Instance;
foreach (var property in type.GetProperties(flags))
{
var propertyType = property.PropertyType;
if (!typeof(IComparable).IsAssignableFrom(propertyType))
throw new NotSupportedException($"{propertyType} props are not supported.");
var propertyValueX = (IComparable)property.GetValue(x);
var propertyValueY = (IComparable)property.GetValue(y);
if (propertyValueX == null && propertyValueY == null)
continue;
if (propertyValueX == null)
return -1;
int result = propertyValueX.CompareTo(property.GetValue(y));
if (result == 0)
continue;
return result;
}
return 0;
}
}
And pass it to sequence comparer
var equal = obj.CompareSequences(test, test1, new SimplePropertiesComparer<Attribute>());

Change the signature of your method and remove the then redundant cast:
public bool CompareList<T>(IList<T> firstList, IList<T> secondList) where T : class
{
var list1 = firstList as IList<T>; // Cast is not necessary any more
return true;
}

public bool CompareGenericLists<T, U>(List<T> list1, List<U> list2)
{
try
{
if (typeof(T).Equals(typeof(U)))
{
//For checking null lists
if (list1 == null && list2 == null)
return true;
if (list1 == null || list2 == null)
throw new Exception("One of the Lists is Null");
if (list1.Count.Equals(list2.Count))
{
Type type = typeof(T);
//For primitive lists
if (type.IsPrimitive)
{
int flag = 0;
for (int i = 0; i < list1.Count; i++)
{
if (list1.ElementAt(i).Equals(list2.ElementAt(i)))
flag++;
}
if (flag != list1.Count)
throw new Exception("Objects values are not same");
}
//For Reference List
else
{
for (int i = 0; i < list1.Count; i++)
{
foreach (System.Reflection.PropertyInfo property in type.GetProperties())
{
string Object1Value = string.Empty;
string Object2Value = string.Empty;
Object1Value = type.GetProperty(property.Name).GetValue(list1.ElementAt(i)).ToString();
Object2Value = type.GetProperty(property.Name).GetValue(list2.ElementAt(i)).ToString();
if (Object1Value != Object2Value)
{
throw new Exception("Objects values are not same");
}
}
}
}
}
else
throw new Exception("Length of lists is not Same");
}
else
throw new Exception("Different type of lists");
}
catch(Exception ex)
{
throw ex;
}
return true;
}
this method can be used for both primitive and reference lists.try this method.It will compare type,counts,and members of lists.

Can a DynamicParameter rely on the values of other DynamicParameters?

I have a GetDynamicParameters() on cmdlet Get-DateSlain that does something like this:
public object GetDynamicParameters()
{
List<string> houseList = {"Stark", "Lannister", "Tully"};
var attributes = new Collection<Attribute>
{
new ParameterAttribute
{
HelpMessage = "Enter a house name",
},
new ValidateSetAttribute(houseList.ToArray()),
};
if (!this.ContainsKey("House"))
{
this.runtimeParameters.Add("House", new RuntimeDefinedParameter("House", typeof(string), attributes));
}
}
And this works as expected - users can type Get-DateSlain -House, and tab through the available houses. However, once a house is chosen, I want to be able to narrow down the results to characters in that house. Furthermore, if it's house 'Stark', I want to allow a -Wolf parameter. So to implement (some value validity checks removed for brevity):
public object GetDynamicParameters()
{
if (this.runtimeParameters.ContainsKey("House"))
{
// We already have this key - no need to re-add. However, now we can add other parameters
var house = this.runtimeParameters["House"].Value.ToString();
if (house == "Stark")
{
List<string> characters = { "Ned", "Arya", "Rob" };
var attributes = new Collection<Attribute>
{
new ParameterAttribute
{
HelpMessage = "Enter a character name",
},
new ValidateSetAttribute(characters.ToArray()),
};
this.runtimeParameters.Add("Character", new RuntimeDefinedParameter("Character", typeof(string), attributes));
List<string> wolves = { "Shaggydog", "Snow", "Lady" };
var attributes = new Collection<Attribute>
{
new ParameterAttribute
{
HelpMessage = "Enter a wolf name",
},
new ValidateSetAttribute(wolves.ToArray()),
};
this.runtimeParameters.Add("Wolf", new RuntimeDefinedParameter("Wolf", typeof(string), attributes));
}
else if (house == "Lannister")
{
List<string> characters = { "Jaimie", "Cersei", "Tywin" };
// ...
}
// ...
return this.runtimeParameters;
}
List<string> houseList = {"Stark", "Lannister", "Tully"};
var attributes = new Collection<Attribute>
{
new ParameterAttribute
{
HelpMessage = "Enter a house name",
},
new ValidateSetAttribute(houseList.ToArray()),
};
this.runtimeParameters.Add("House", new RuntimeDefinedParameter("House", typeof(string), attributes));
}
This looks like it should work, but it doesn't. The GetDynamicParameters function is only called once, and that is before a value is supplied to this.runtimeParameters["House"]. Since it doesn't re-evaluate after that value is filled in, the additional field(s) are never added, and any logic in ProcessRecord that relies on these fields will fail.
So - is there a way to have multiple dynamic parameters that rely on each other?

Have a look a the aswer to this question, it shows a way to access the values of other dynamic parameters in the GetDynamicParameters method:
Powershell module: Dynamic mandatory hierarchical parameters
I adapted the code from the mentioned answer so it can handle SwitchParameters and the raw input parameter is converted to the actual type of the cmdlet parameter. It does not work if the dynamic parameter you want to get the value for is passed via pipeline. I think that is not possible because dynamic parameters are always created before pipeline input is evaluated. Here it is:
public static class DynamicParameterExtension
{
public static T GetUnboundValue<T>(this PSCmdlet cmdlet, string paramName, int unnamedPosition = -1))
{
var context = TryGetProperty(cmdlet, "Context");
var processor = TryGetProperty(context, "CurrentCommandProcessor");
var parameterBinder = TryGetProperty(processor, "CmdletParameterBinderController");
var args = TryGetProperty(parameterBinder, "UnboundArguments") as System.Collections.IEnumerable;
if (args != null)
{
var isSwitch = typeof(SwitchParameter) == typeof(T);
var currentParameterName = string.Empty;
object unnamedValue = null;
var i = 0;
foreach (var arg in args)
{
var isParameterName = TryGetProperty(arg, "ParameterNameSpecified");
if (isParameterName != null && true.Equals(isParameterName))
{
var parameterName = TryGetProperty(arg, "ParameterName") as string;
currentParameterName = parameterName;
if (isSwitch && string.Equals(currentParameterName, paramName, StringComparison.OrdinalIgnoreCase))
{
return (T)(object)new SwitchParameter(true);
}
continue;
}
var parameterValue = TryGetProperty(arg, "ArgumentValue");
if (currentParameterName != string.Empty)
{
if (string.Equals(currentParameterName, paramName, StringComparison.OrdinalIgnoreCase))
{
return ConvertParameter<T>(parameterValue);
}
}
else if (i++ == unnamedPosition)
{
unnamedValue = parameterValue;
}
currentParameterName = string.Empty;
}
if (unnamedValue != null)
{
return ConvertParameter<T>(unnamedValue);
}
}
return default(T);
}
static T ConvertParameter<T>(this object value)
{
if (value == null || Equals(value, default(T)))
{
return default(T);
}
var psObject = value as PSObject;
if (psObject != null)
{
return psObject.BaseObject.ConvertParameter<T>();
}
if (value is T)
{
return (T)value;
}
var constructorInfo = typeof(T).GetConstructor(new[] { value.GetType() });
if (constructorInfo != null)
{
return (T)constructorInfo.Invoke(new[] { value });
}
try
{
return (T)Convert.ChangeType(value, typeof(T));
}
catch (Exception)
{
return default(T);
}
}
static object TryGetProperty(object instance, string fieldName)
{
if (instance == null || string.IsNullOrEmpty(fieldName))
{
return null;
}
const BindingFlags bindingFlags = BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static | BindingFlags.Public;
var propertyInfo = instance.GetType().GetProperty(fieldName, bindingFlags);
try
{
if (propertyInfo != null)
{
return propertyInfo.GetValue(instance, null);
}
var fieldInfo = instance.GetType().GetField(fieldName, bindingFlags);
return fieldInfo?.GetValue(instance);
}
catch (Exception)
{
return null;
}
}
}
So for your example you should be able to use it like:
public object GetDynamicParameters()
{
var houseList = new List<string> { "Stark", "Lannister", "Tully" };
var attributes = new Collection<Attribute>
{
new ParameterAttribute { HelpMessage = "Enter a house name" },
new ValidateSetAttribute(houseList.ToArray()),
};
var runtimeParameters = new RuntimeDefinedParameterDictionary
{
{"House", new RuntimeDefinedParameter("House", typeof (string), attributes)}
};
var selectedHouse = this.GetUnboundValue<string>("House");
//... add parameters dependant on value of selectedHouse
return runtimeParameters;
}
After all I'm not sure if it's a good idea trying to get those dynamic parameter values in the first place. It is obviously not supported by PowerShell Cmdlet API (see all the reflection to access private members in the GetUnboundValue method), you have to reimplement the PowerShell parameter conversion magic (see ConvertParameter, I'm sure I missed some cases there) and there is the restriction with pipelined values. Usage at your own risk:)

Compare Properties automatically

I want to get the names of all properties that changed for matching objects. I have these (simplified) classes:
public enum PersonType { Student, Professor, Employee }
class Person {
public string Name { get; set; }
public PersonType Type { get; set; }
}
class Student : Person {
public string MatriculationNumber { get; set; }
}
class Subject {
public string Name { get; set; }
public int WeeklyHours { get; set; }
}
class Professor : Person {
public List<Subject> Subjects { get; set; }
}
Now I want to get the objects where the Property values differ:
List<Person> oldPersonList = ...
List<Person> newPersonList = ...
List<Difference> = GetDifferences(oldPersonList, newPersonList);
public List<Difference> GetDifferences(List<Person> oldP, List<Person> newP) {
//how to check the properties without casting and checking
//for each type and individual property??
//can this be done with Reflection even in Lists??
}
In the end I would like to have a list of Differences like this:
class Difference {
public List<string> ChangedProperties { get; set; }
public Person NewPerson { get; set; }
public Person OldPerson { get; set; }
}
The ChangedProperties should contain the name of the changed properties.

I've spent quite a while trying to write a faster reflection-based solution using typed delegates. But eventually I gave up and switched to Marc Gravell's Fast-Member library to achieve higher performance than with normal reflection.
Code:
internal class PropertyComparer
{
public static IEnumerable<Difference<T>> GetDifferences<T>(PropertyComparer pc,
IEnumerable<T> oldPersons,
IEnumerable<T> newPersons)
where T : Person
{
Dictionary<string, T> newPersonMap = newPersons.ToDictionary(p => p.Name, p => p);
foreach (T op in oldPersons)
{
// match items from the two lists by the 'Name' property
if (newPersonMap.ContainsKey(op.Name))
{
T np = newPersonMap[op.Name];
Difference<T> diff = pc.SearchDifferences(op, np);
if (diff != null)
{
yield return diff;
}
}
}
}
private Difference<T> SearchDifferences<T>(T obj1, T obj2)
{
CacheObject(obj1);
CacheObject(obj2);
return SimpleSearch(obj1, obj2);
}
private Difference<T> SimpleSearch<T>(T obj1, T obj2)
{
Difference<T> diff = new Difference<T>
{
ChangedProperties = new List<string>(),
OldPerson = obj1,
NewPerson = obj2
};
ObjectAccessor obj1Getter = ObjectAccessor.Create(obj1);
ObjectAccessor obj2Getter = ObjectAccessor.Create(obj2);
var propertyList = _propertyCache[obj1.GetType()];
// find the common properties if types differ
if (obj1.GetType() != obj2.GetType())
{
propertyList = propertyList.Intersect(_propertyCache[obj2.GetType()]).ToList();
}
foreach (string propName in propertyList)
{
// fetch the property value via the ObjectAccessor
if (!obj1Getter[propName].Equals(obj2Getter[propName]))
{
diff.ChangedProperties.Add(propName);
}
}
return diff.ChangedProperties.Count > 0 ? diff : null;
}
// cache for the expensive reflections calls
private Dictionary<Type, List<string>> _propertyCache = new Dictionary<Type, List<string>>();
private void CacheObject<T>(T obj)
{
if (!_propertyCache.ContainsKey(obj.GetType()))
{
_propertyCache[obj.GetType()] = new List<string>();
_propertyCache[obj.GetType()].AddRange(obj.GetType().GetProperties().Select(pi => pi.Name));
}
}
}
Usage:
PropertyComparer pc = new PropertyComparer();
var diffs = PropertyComparer.GetDifferences(pc, oldPersonList, newPersonList).ToList();
Performance:
My very biased measurements showed that this approach is about 4-6 times faster than the Json-Conversion and about 9 times faster than ordinary reflections. But in fairness, you could probably speed up the other solutions quite a bit.
Limitations:
At the moment my solution doesn't recurse over nested lists, for example it doesn't compare individual Subject items - it only detects that the subjects lists are different, but not what or where. However, it shouldn't be too hard to add this feature when you need it. The most difficult part would probably be to decide how to represent these differences in the Difference class.

We start with 2 simple methods:
public bool AreEqual(object leftValue, object rightValue)
{
var left = JsonConvert.SerializeObject(leftValue);
var right = JsonConvert.SerializeObject(rightValue);
return left == right;
}
public Difference<T> GetDifference<T>(T newItem, T oldItem)
{
var properties = typeof(T).GetProperties();
var propertyValues = properties
.Select(p => new {
p.Name,
LeftValue = p.GetValue(newItem),
RightValue = p.GetValue(oldItem)
});
var differences = propertyValues
.Where(p => !AreEqual(p.LeftValue, p.RightValue))
.Select(p => p.Name)
.ToList();
return new Difference<T>
{
ChangedProperties = differences,
NewItem = newItem,
OldItem = oldItem
};
}
AreEqual just compares the serialized versions of two objects using Json.Net, this keeps it from treating reference types and value types differently.
GetDifference checks the properties on the passed in objects and compares them individually.
To get a list of differences:
var oldPersonList = new List<Person> {
new Person { Name = "Bill" },
new Person { Name = "Bob" }
};
var newPersonList = new List<Person> {
new Person { Name = "Bill" },
new Person { Name = "Bobby" }
};
var diffList = oldPersonList.Zip(newPersonList, GetDifference)
.Where(d => d.ChangedProperties.Any())
.ToList();

Everyone always tries to get fancy and write these overly generic ways of extracting data. There is a cost to that.
Why not be old school simple.
Have a GetDifferences member function Person.
virtual List<String> GetDifferences(Person otherPerson){
var diffs = new List<string>();
if(this.X != otherPerson.X) diffs.add("X");
....
}
In inherited classes. Override and add their specific properties. AddRange the base function.
KISS - Keep it simple. It would take you 10 minutes of monkey work to write it, and you know it will be efficient and work.

I am doing it by using this:
//This structure represents the comparison of one member of an object to the corresponding member of another object.
public struct MemberComparison
{
public static PropertyInfo NullProperty = null; //used for ROOT properties - i dont know their name only that they are changed
public readonly MemberInfo Member; //Which member this Comparison compares
public readonly object Value1, Value2;//The values of each object's respective member
public MemberComparison(PropertyInfo member, object value1, object value2)
{
Member = member;
Value1 = value1;
Value2 = value2;
}
public override string ToString()
{
return Member.name+ ": " + Value1.ToString() + (Value1.Equals(Value2) ? " == " : " != ") + Value2.ToString();
}
}
//This method can be used to get a list of MemberComparison values that represent the fields and/or properties that differ between the two objects.
public static List<MemberComparison> ReflectiveCompare<T>(T x, T y)
{
List<MemberComparison> list = new List<MemberComparison>();//The list to be returned
if (x.GetType().IsArray)
{
Array xArray = x as Array;
Array yArray = y as Array;
if (xArray.Length != yArray.Length)
list.Add(new MemberComparison(MemberComparison.NullProperty, "array", "array"));
else
{
for (int i = 0; i < xArray.Length; i++)
{
var compare = ReflectiveCompare(xArray.GetValue(i), yArray.GetValue(i));
if (compare.Count > 0)
list.AddRange(compare);
}
}
}
else
{
foreach (PropertyInfo m in x.GetType().GetProperties())
//Only look at fields and properties.
//This could be changed to include methods, but you'd have to get values to pass to the methods you want to compare
if (!m.PropertyType.IsArray && (m.PropertyType == typeof(String) || m.PropertyType == typeof(double) || m.PropertyType == typeof(int) || m.PropertyType == typeof(uint) || m.PropertyType == typeof(float)))
{
var xValue = m.GetValue(x, null);
var yValue = m.GetValue(y, null);
if (!object.Equals(yValue, xValue))//Add a new comparison to the list if the value of the member defined on 'x' isn't equal to the value of the member defined on 'y'.
list.Add(new MemberComparison(m, yValue, xValue));
}
else if (m.PropertyType.IsArray)
{
Array xArray = m.GetValue(x, null) as Array;
Array yArray = m.GetValue(y, null) as Array;
if (xArray.Length != yArray.Length)
list.Add(new MemberComparison(m, "array", "array"));
else
{
for (int i = 0; i < xArray.Length; i++)
{
var compare = ReflectiveCompare(xArray.GetValue(i), yArray.GetValue(i));
if (compare.Count > 0)
list.AddRange(compare);
}
}
}
else if (m.PropertyType.IsClass)
{
var xValue = m.GetValue(x, null);
var yValue = m.GetValue(y, null);
if ((xValue == null || yValue == null) && !(yValue == null && xValue == null))
list.Add(new MemberComparison(m, xValue, yValue));
else if (!(xValue == null || yValue == null))
{
var compare = ReflectiveCompare(m.GetValue(x, null), m.GetValue(y, null));
if (compare.Count > 0)
list.AddRange(compare);
}
}
}
return list;
}

Here you have a code which does what you want with Reflection.
public List<Difference> GetDifferences(List<Person> oldP, List<Person> newP)
{
List<Difference> allDiffs = new List<Difference>();
foreach (Person oldPerson in oldP)
{
foreach (Person newPerson in newP)
{
Difference curDiff = GetDifferencesTwoPersons(oldPerson, newPerson);
allDiffs.Add(curDiff);
}
}
return allDiffs;
}
private Difference GetDifferencesTwoPersons(Person OldPerson, Person NewPerson)
{
MemberInfo[] members = typeof(Person).GetMembers();
Difference returnDiff = new Difference();
returnDiff.NewPerson = NewPerson;
returnDiff.OldPerson = OldPerson;
returnDiff.ChangedProperties = new List<string>();
foreach (MemberInfo member in members)
{
if (member.MemberType == MemberTypes.Property)
{
if (typeof(Person).GetProperty(member.Name).GetValue(NewPerson, null).ToString() != typeof(Person).GetProperty(member.Name).GetValue(OldPerson, null).ToString())
{
returnDiff.ChangedProperties.Add(member.Name);
}
}
}
return returnDiff;
}

C# Reflection Indexed Properties

I am writing a Clone method using reflection. How do I detect that a property is an indexed property using reflection? For example:
public string[] Items
{
get;
set;
}
My method so far:
public static T Clone<T>(T from, List<string> propertiesToIgnore) where T : new()
{
T to = new T();
Type myType = from.GetType();
PropertyInfo[] myProperties = myType.GetProperties();
for (int i = 0; i < myProperties.Length; i++)
{
if (myProperties[i].CanWrite && !propertiesToIgnore.Contains(myProperties[i].Name))
{
myProperties[i].SetValue(to,myProperties[i].GetValue(from,null),null);
}
}
return to;
}

if (propertyInfo.GetIndexParameters().Length > 0)
{
// Property is an indexer
}

Sorry, but
public string[] Items { get; set; }
is not an indexed property, it's merely of an array type!
However the following is:
public string this[int index]
{
get { ... }
set { ... }
}

What you want is the GetIndexParameters() method. If the array that it returns has more than 0 items, that means it's an indexed property.
See the MSDN documentation for more details.

If you call property.GetValue(obj,null), and the property IS indexed, then you will get a parameter count mismatch exception. Better to check whether the property is indexed using GetIndexParameters() and then decide what to do.

Here is some code that worked for me:
foreach (PropertyInfo property in obj.GetType().GetProperties())
{
object value = property.GetValue(obj, null);
if (value is object[])
{
....
}
}
P.S. .GetIndexParameters().Length > 0) works for the case described in this article: http://msdn.microsoft.com/en-us/library/b05d59ty.aspx
So if you care about the property named Chars for a value of type string, use that, but it does not work for most of the arrays I was interested in, including, I am pretty sure, a string array from the original question.

You can convert the indexer to IEnumerable
public static IEnumerable<T> AsEnumerable<T>(this object o) where T : class {
var list = new List<T>();
System.Reflection.PropertyInfo indexerProperty = null;
foreach (System.Reflection.PropertyInfo pi in o.GetType().GetProperties()) {
if (pi.GetIndexParameters().Length > 0) {
indexerProperty = pi;
break;
}
}
if (indexerProperty.IsNotNull()) {
var len = o.GetPropertyValue<int>("Length");
for (int i = 0; i < len; i++) {
var item = indexerProperty.GetValue(o, new object[]{i});
if (item.IsNotNull()) {
var itemObject = item as T;
if (itemObject.IsNotNull()) {
list.Add(itemObject);
}
}
}
}
return list;
}
public static bool IsNotNull(this object o) {
return o != null;
}
public static T GetPropertyValue<T>(this object source, string property) {
if (source == null)
throw new ArgumentNullException("source");
var sourceType = source.GetType();
var sourceProperties = sourceType.GetProperties();
var properties = sourceProperties
.Where(s => s.Name.Equals(property));
if (properties.Count() == 0) {
sourceProperties = sourceType.GetProperties(BindingFlags.Instance | BindingFlags.NonPublic);
properties = sourceProperties.Where(s => s.Name.Equals(property));
}
if (properties.Count() > 0) {
var propertyValue = properties
.Select(s => s.GetValue(source, null))
.FirstOrDefault();
return propertyValue != null ? (T)propertyValue : default(T);
}
return default(T);
}