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Check if a method can be invoked with the array of parameters

I'm invoking a method using reflection but i want to check that the array of parameters i have are of the correct type before doing so. I've tried several methods like Type.IsAssignableFrom and other comparisons, but they still give false positives. For example when using an int as parameter to a function that accepts an enum.
The reference source seems to do exactly this check, is this exposed somewhere?
My current code looks like this:
private bool CheckTypeMatch(ParameterInfo[] methodParameters, Type[] callParameterTypes)
{
if (methodParameters.Length < callParameterTypes.Length)
{
return false;
}
for (int index = 0; index < callParameterTypes.Length; index++)
{
Type type = methodParameters[index].ParameterType;
if (callParameterTypes[index] != null && !type.IsAssignableFrom(callParameterTypes[index]) && !(type.IsEnum && System.Enum.GetUnderlyingType(type).IsAssignableFrom(callParameterTypes[index])))
{
return false;
}
}
return true;
}
I am worried there are more cases where the type of the parameter is actually compatible with the method but is being rejected by this function.
Thanks in advance!

Get the name of parameters from a calling method

I have a project using C# .NET 2.0 (cannot use a higher version). I would like to get the name of the parameters of a method in a method called by the first one. If I call a method from the MyMethodsClass, I want to receive a string indicating which parameter is not valid, following some conditions indicated in the isValid method from the MyCheckClass class.
With the following code, I get a string that returns "Please check the 5 parameter" in case I would call the myMehtod(5,1,1). But I would like to obtain, "Please check the a parameter".
How could I do that?
Thank you!
public MyMethodsClass {
public string myMethod (int a, int b, int c) {
return MyCheckClass.isValid(a,b,c);
}
public string myMethod2 (int d, int e) {
return MyCheckClass.isValid(d,e);
}
}
//Other file
public class MyCheckClass {
public static string isValid (params object[] parameters) {
StringBuilder result= new StringBuilder();
for (int i = 0; i < parameters.Length; i++)
{
object p = parameters[i];
//Some checks...
if (p == null || p.Equals("") || p != 5)
{
result.Append("Please check the " + p + " parameter");
}
}
return result.toString();
}
}

You combine two things you already know how to do.
How can I find the method that called the current method?
How can you get the names of method parameters in C#?

These two line should do the job for you, perhaps need to adapt but should work ^^
MethodInfo info = typeof (MyMethodsClass).GetMethod("MethodName");
string name = info.GetParameters()[indexOfTheFaultyOne].Name;

Dynamically calling a dll and method with arguments

Basically I'm trying to call a dll by name, instantiate an object, then call a method by name in that dll. I'm getting an "Exception has been thrown by the target of an invocation." during the Method.Invoke. I'm fairly sure my problem is with the typecasting of the arguments of the method. I was wondering if anyone had any input on this exception. Additionally, any suggestions on how to revise my approach are welcome.
public void calldll(string dllName, string typeName, string methodName, string arguments) {
string[] argumentArray = arguments.Split(new char[] { '|' }, StringSplitOptions.None);
Assembly assembly = Assembly.LoadFrom(dllName);
System.Type type = assembly.GetType(typeName);
Object o = Activator.CreateInstance(type);
MethodInfo method = type.GetMethod(methodName);
ParameterInfo[] parameters = method.GetParameters();
object[] methodParameters = new object[parameters.GetLength(0)];
for (int i = 0; i < parameters.Length - 1; i++)
{
var converter = TypeDescriptor.GetConverter(parameters[i].GetType());
methodParameters[i] = converter.ConvertFrom(argumentArray[i]);
}
method.Invoke(o, methodParameters); }

I found two issues with your code:
You are not looping over all parameters. You should remove -1 from the for loop.
When you are creating your converter, you call the GetType() method. This returns the Type of the ParameterInfo object, not the Type of the parameter. Use the property ParameterType instead.
All in all, change the first lines in the for loop to this:
for (int i = 0; i < parameters.Length; i++)
{
var converter = TypeDescriptor.GetConverter(parameters[i].ParameterType);
Once you have done these corrections, I believe your code should run as intended. At least it did for me when I tested a simple void Hello(int x, string y) method.

Test if a property is available on a dynamic variable

My situation is very simple. Somewhere in my code I have this:
dynamic myVariable = GetDataThatLooksVerySimilarButNotTheSame();
//How to do this?
if (myVariable.MyProperty.Exists)
//Do stuff
So, basically my question is how to check (without throwing an exception) that a certain property is available on my dynamic variable. I could do GetType() but I'd rather avoid that since I don't really need to know the type of the object. All that I really want to know is whether a property (or method, if that makes life easier) is available. Any pointers?

I think there is no way to find out whether a dynamic variable has a certain member without trying to access it, unless you re-implemented the way dynamic binding is handled in the C# compiler. Which would probably include a lot of guessing, because it is implementation-defined, according to the C# specification.
So you should actually try to access the member and catch an exception, if it fails:
dynamic myVariable = GetDataThatLooksVerySimilarButNotTheSame();
try
{
var x = myVariable.MyProperty;
// do stuff with x
}
catch (RuntimeBinderException)
{
// MyProperty doesn't exist
}

I thought I'd do a comparison of Martijn's answer and svick's answer...
The following program returns the following results:
Testing with exception: 2430985 ticks
Testing with reflection: 155570 ticks
void Main()
{
var random = new Random(Environment.TickCount);
dynamic test = new Test();
var sw = new Stopwatch();
sw.Start();
for (int i = 0; i < 100000; i++)
{
TestWithException(test, FlipCoin(random));
}
sw.Stop();
Console.WriteLine("Testing with exception: " + sw.ElapsedTicks.ToString() + " ticks");
sw.Restart();
for (int i = 0; i < 100000; i++)
{
TestWithReflection(test, FlipCoin(random));
}
sw.Stop();
Console.WriteLine("Testing with reflection: " + sw.ElapsedTicks.ToString() + " ticks");
}
class Test
{
public bool Exists { get { return true; } }
}
bool FlipCoin(Random random)
{
return random.Next(2) == 0;
}
bool TestWithException(dynamic d, bool useExisting)
{
try
{
bool result = useExisting ? d.Exists : d.DoesntExist;
return true;
}
catch (Exception)
{
return false;
}
}
bool TestWithReflection(dynamic d, bool useExisting)
{
Type type = d.GetType();
return type.GetProperties().Any(p => p.Name.Equals(useExisting ? "Exists" : "DoesntExist"));
}
As a result I'd suggest using reflection. See below.
Responding to bland's comment:
Ratios are reflection:exception ticks for 100000 iterations:
Fails 1/1: - 1:43 ticks
Fails 1/2: - 1:22 ticks
Fails 1/3: - 1:14 ticks
Fails 1/5: - 1:9 ticks
Fails 1/7: - 1:7 ticks
Fails 1/13: - 1:4 ticks
Fails 1/17: - 1:3 ticks
Fails 1/23: - 1:2 ticks
...
Fails 1/43: - 1:2 ticks
Fails 1/47: - 1:1 ticks
...fair enough - if you expect it to fail with a probability with less than ~1/47, then go for exception.
The above assumes that you're running GetProperties() each time. You may be able to speed up the process by caching the result of GetProperties() for each type in a dictionary or similar. This may help if you're checking against the same set of types over and again.

Maybe use reflection?
dynamic myVar = GetDataThatLooksVerySimilarButNotTheSame();
Type typeOfDynamic = myVar.GetType();
bool exist = typeOfDynamic.GetProperties().Where(p => p.Name.Equals("PropertyName")).Any();

Just in case it helps someone:
If the method GetDataThatLooksVerySimilarButNotTheSame() returns an ExpandoObject you can also cast to a IDictionary before checking.
dynamic test = new System.Dynamic.ExpandoObject();
test.foo = "bar";
if (((IDictionary<string, object>)test).ContainsKey("foo"))
{
Console.WriteLine(test.foo);
}

The two common solutions to this include making the call and catching the RuntimeBinderException, using reflection to check for the call, or serialising to a text format and parsing from there. The problem with exceptions is that they are very slow, because when one is constructed, the current call stack is serialised. Serialising to JSON or something analogous incurs a similar penalty. This leaves us with reflection but it only works if the underlying object is actually a POCO with real members on it. If it's a dynamic wrapper around a dictionary, a COM object, or an external web service, then reflection won't help.
Another solution is to use IDynamicMetaObjectProvider to get the member names as the DLR sees them. In the example below, I use a static class (Dynamic) to test for the Age field and display it.
class Program
{
static void Main()
{
dynamic x = new ExpandoObject();
x.Name = "Damian Powell";
x.Age = "21 (probably)";
if (Dynamic.HasMember(x, "Age"))
{
Console.WriteLine("Age={0}", x.Age);
}
}
}
public static class Dynamic
{
public static bool HasMember(object dynObj, string memberName)
{
return GetMemberNames(dynObj).Contains(memberName);
}
public static IEnumerable<string> GetMemberNames(object dynObj)
{
var metaObjProvider = dynObj as IDynamicMetaObjectProvider;
if (null == metaObjProvider) throw new InvalidOperationException(
"The supplied object must be a dynamic object " +
"(i.e. it must implement IDynamicMetaObjectProvider)"
);
var metaObj = metaObjProvider.GetMetaObject(
Expression.Constant(metaObjProvider)
);
var memberNames = metaObj.GetDynamicMemberNames();
return memberNames;
}
}

Denis's answer made me think to another solution using JsonObjects,
a header property checker:
Predicate<object> hasHeader = jsonObject =>
((JObject)jsonObject).OfType<JProperty>()
.Any(prop => prop.Name == "header");
or maybe better:
Predicate<object> hasHeader = jsonObject =>
((JObject)jsonObject).Property("header") != null;
for example:
dynamic json = JsonConvert.DeserializeObject(data);
string header = hasHeader(json) ? json.header : null;

Well, I faced a similar problem but on unit tests.
Using SharpTestsEx you can check if a property existis. I use this testing my controllers, because since the JSON object is dynamic, someone can change the name and forget to change it in the javascript or something, so testing for all properties when writing the controller should increase my safety.
Example:
dynamic testedObject = new ExpandoObject();
testedObject.MyName = "I am a testing object";
Now, using SharTestsEx:
Executing.This(delegate {var unused = testedObject.MyName; }).Should().NotThrow();
Executing.This(delegate {var unused = testedObject.NotExistingProperty; }).Should().Throw();
Using this, i test all existing properties using "Should().NotThrow()".
It's probably out of topic, but can be usefull for someone.

Following on from the answer by #karask, you could wrap the function as a helper like so:
public static bool HasProperty(ExpandoObject expandoObj,
string name)
{
return ((IDictionary<string, object>)expandoObj).ContainsKey(name);
}

For me this works:
if (IsProperty(() => DynamicObject.MyProperty))
; // do stuff
delegate string GetValueDelegate();
private bool IsProperty(GetValueDelegate getValueMethod)
{
try
{
//we're not interesting in the return value.
//What we need to know is whether an exception occurred or not
var v = getValueMethod();
return v != null;
}
catch (RuntimeBinderException)
{
return false;
}
catch
{
return true;
}
}

If you control the type being used as dynamic, couldn't you return a tuple instead of a value for every property access? Something like...
public class DynamicValue<T>
{
internal DynamicValue(T value, bool exists)
{
Value = value;
Exists = exists;
}
T Value { get; private set; }
bool Exists { get; private set; }
}
Possibly a naive implementation, but if you construct one of these internally each time and return that instead of the actual value, you can check Exists on every property access and then hit Value if it does with value being default(T) (and irrelevant) if it doesn't.
That said, I might be missing some knowledge on how dynamic works and this might not be a workable suggestion.

If your use case is to convert an api response, carrying about only a few fields, you can use this:
var template = new { address = new { street = "" } };
var response = JsonConvert.DeserializeAnonymousType(await result.Content.ReadAsStringAsync(), template);
string street = response?.address?.street;

Here is the other way:
using Newtonsoft.Json.Linq;
internal class DymanicTest
{
public static string Json = #"{
""AED"": 3.672825,
""AFN"": 56.982875,
""ALL"": 110.252599,
""AMD"": 408.222002,
""ANG"": 1.78704,
""AOA"": 98.192249,
""ARS"": 8.44469
}";
public static void Run()
{
dynamic dynamicObject = JObject.Parse(Json);
foreach (JProperty variable in dynamicObject)
{
if (variable.Name == "AMD")
{
var value = variable.Value;
}
}
}
}

In my case, I needed to check for the existence of a method with a specific name, so I used an interface for that
var plugin = this.pluginFinder.GetPluginIfInstalled<IPlugin>(pluginName) as dynamic;
if (plugin != null && plugin is ICustomPluginAction)
{
plugin.CustomPluginAction(action);
}
Also, interfaces can contain more than just methods:
Interfaces can contain methods, properties, events, indexers, or any
combination of those four member types.
From: Interfaces (C# Programming Guide)
Elegant and no need to trap exceptions or play with reflexion...

I know this is really old post but here is a simple solution to work with dynamic type in c#.
can use simple reflection to enumerate direct properties
or can use the object extention method
or use GetAsOrDefault<int> method to get a new strongly typed object with value if exists or default if not exists.
public static class DynamicHelper
{
private static void Test( )
{
dynamic myobj = new
{
myInt = 1,
myArray = new[ ]
{
1, 2.3
},
myDict = new
{
myInt = 1
}
};
var myIntOrZero = myobj.GetAsOrDefault< int >( ( Func< int > )( ( ) => myobj.noExist ) );
int? myNullableInt = GetAs< int >( myobj, ( Func< int > )( ( ) => myobj.myInt ) );
if( default( int ) != myIntOrZero )
Console.WriteLine( $"myInt: '{myIntOrZero}'" );
if( default( int? ) != myNullableInt )
Console.WriteLine( $"myInt: '{myNullableInt}'" );
if( DoesPropertyExist( myobj, "myInt" ) )
Console.WriteLine( $"myInt exists and it is: '{( int )myobj.myInt}'" );
}
public static bool DoesPropertyExist( dynamic dyn, string property )
{
var t = ( Type )dyn.GetType( );
var props = t.GetProperties( );
return props.Any( p => p.Name.Equals( property ) );
}
public static object GetAs< T >( dynamic obj, Func< T > lookup )
{
try
{
var val = lookup( );
return ( T )val;
}
catch( RuntimeBinderException ) { }
return null;
}
public static T GetAsOrDefault< T >( this object obj, Func< T > test )
{
try
{
var val = test( );
return ( T )val;
}
catch( RuntimeBinderException ) { }
return default( T );
}
}

As ExpandoObject inherits the IDictionary<string, object> you can use the following check
dynamic myVariable = GetDataThatLooksVerySimilarButNotTheSame();
if (((IDictionary<string, object>)myVariable).ContainsKey("MyProperty"))
//Do stuff
You can make a utility method to perform this check, that will make the code much cleaner and re-usable

How do I create and access a new instance of an Anonymous Class passed as a parameter in C#?

I have created a function that takes a SQL command and produces output that can then be used to fill a List of class instances. The code works great. I've included a slightly simplified version without exception handling here just for reference - skip this code if you want to jump right the problem. If you have suggestions here, though, I'm all ears.
public List<T> ReturnList<T>() where T : new()
{
List<T> fdList = new List<T>();
myCommand.CommandText = QueryString;
SqlDataReader nwReader = myCommand.ExecuteReader();
Type objectType = typeof (T);
FieldInfo[] typeFields = objectType.GetFields();
while (nwReader.Read())
{
T obj = new T();
foreach (FieldInfo info in typeFields)
{
for (int i = 0; i < nwReader.FieldCount; i++)
{
if (info.Name == nwReader.GetName(i))
{
info.SetValue(obj, nwReader[i]);
break;
}
}
}
fdList.Add(obj);
}
nwReader.Close();
return fdList;
}
As I say, this works just fine. However, I'd like to be able to call a similar function with an anonymous class for obvious reasons.
Question #1: it appears that I must construct an anonymous class instance in my call to my anonymous version of this function - is this right? An example call is:
.ReturnList(new { ClientID = 1, FirstName = "", LastName = "", Birthdate = DateTime.Today });
Question #2: the anonymous version of my ReturnList function is below. Can anyone tell me why the call to info.SetValue simply does nothing? It doesn't return an error or anything but neither does it change the value of the target field.
public List<T> ReturnList<T>(T sample)
{
List<T> fdList = new List<T>();
myCommand.CommandText = QueryString;
SqlDataReader nwReader = myCommand.ExecuteReader();
// Cannot use FieldInfo[] on the type - it finds no fields.
var properties = TypeDescriptor.GetProperties(sample);
while (nwReader.Read())
{
// No way to create a constructor so this call creates the object without calling a ctor. Could this be a source of the problem?
T obj = (T)FormatterServices.GetUninitializedObject(typeof(T));
foreach (PropertyDescriptor info in properties)
{
for (int i = 0; i < nwReader.FieldCount; i++)
{
if (info.Name == nwReader.GetName(i))
{
// This loop runs fine but there is no change to obj!!
info.SetValue(obj, nwReader[i]);
break;
}
}
}
fdList.Add(obj);
}
nwReader.Close();
return fdList;
}
Any ideas?
Note: when I tried to use the FieldInfo array as I did in the function above, the typeFields array had zero elements (even though the objectType shows the field names - strange). Thus, I use TypeDescriptor.GetProperties instead.
Any other tips and guidance on the use of reflection or anonymous classes are appropriate here - I'm relatively new to this specific nook of the C# language.
UPDATE: I have to thank Jason for the key to solving this. Below is the revised code that will create a list of anonymous class instances, filling the fields of each instance from a query.
public List<T> ReturnList<T>(T sample)
{
List<T> fdList = new List<T>();
myCommand.CommandText = QueryString;
SqlDataReader nwReader = myCommand.ExecuteReader();
var properties = TypeDescriptor.GetProperties(sample);
while (nwReader.Read())
{
int objIdx = 0;
object[] objArray = new object[properties.Count];
foreach (PropertyDescriptor info in properties)
objArray[objIdx++] = nwReader[info.Name];
fdList.Add((T)Activator.CreateInstance(sample.GetType(), objArray));
}
nwReader.Close();
return fdList;
}
Note that the query has been constructed and the parameters initialized in previous calls to this object's methods. The original code had an inner/outer loop combination so that the user could have fields in their anonymous class that didn't match a field. However, in order to simplify the design, I've decided not to permit this and have instead adopted the db field access recommended by Jason. Also, thanks to Dave Markle as well for helping me understand more about the tradeoffs in using Activator.CreateObject() versus GenUninitializedObject.

Anonymous types encapsulate a set of read-only properties. This explains
Why Type.GetFields returns an empty array when called on your anonymous type: anonymous types do not have public fields.
The public properties on an anonymous type are read-only and can not have their value set by a call to PropertyInfo.SetValue. If you call PropertyInfo.GetSetMethod on a property in an anonymous type, you will receive back null.
In fact, if you change
var properties = TypeDescriptor.GetProperties(sample);
while (nwReader.Read()) {
// No way to create a constructor so this call creates the object without calling a ctor. Could this be a source of the problem?
T obj = (T)FormatterServices.GetUninitializedObject(typeof(T));
foreach (PropertyDescriptor info in properties) {
for (int i = 0; i < nwReader.FieldCount; i++) {
if (info.Name == nwReader.GetName(i)) {
// This loop runs fine but there is no change to obj!!
info.SetValue(obj, nwReader[i]);
break;
}
}
}
fdList.Add(obj);
}
to
PropertyInfo[] properties = sample.GetType().GetProperties();
while (nwReader.Read()) {
// No way to create a constructor so this call creates the object without calling a ctor. Could this be a source of the problem?
T obj = (T)FormatterServices.GetUninitializedObject(typeof(T));
foreach (PropertyInfo info in properties) {
for (int i = 0; i < nwReader.FieldCount; i++) {
if (info.Name == nwReader.GetName(i)) {
// This loop will throw an exception as PropertyInfo.GetSetMethod fails
info.SetValue(obj, nwReader[i], null);
break;
}
}
}
fdList.Add(obj);
}
you will receive an exception informing you that the property set method can not be found.
Now, to solve your problem, what you can do is use Activator.CreateInstance. I'm sorry that I'm too lazy to type out the code for you, but the following will demonstrate how to use it.
var car = new { Make = "Honda", Model = "Civic", Year = 2008 };
var anothercar = Activator.CreateInstance(car.GetType(), new object[] { "Ford", "Focus", 2005 });
So just run through a loop, as you've done, to fill up the object array that you need to pass to Activator.CreateInstance and then call Activator.CreateInstance when the loop is done. Property order is important here as two anonymous types are the same if and only if they have the same number of properties with the same type and same name in the same order.
For more, see the MSDN page on anonymous types.
Lastly, and this is really an aside and not germane to your question, but the following code
foreach (PropertyDescriptor info in properties) {
for (int i = 0; i < nwReader.FieldCount; i++) {
if (info.Name == nwReader.GetName(i)) {
// This loop runs fine but there is no change to obj!!
info.SetValue(obj, nwReader[i]);
break;
}
}
}
could be simplified by
foreach (PropertyDescriptor info in properties) {
info.SetValue(obj, nwReader[info.Name]);
}

I had the same problem, I resolved it by creating a new Linq.Expression that's going to do the real job and compiling it into a lambda: here's my code for example:
I want to transform that call:
var customers = query.ToList(r => new
{
Id = r.Get<int>("Id"),
Name = r.Get<string>("Name"),
Age = r.Get<int>("Age"),
BirthDate = r.Get<DateTime?>("BirthDate"),
Bio = r.Get<string>("Bio"),
AccountBalance = r.Get<decimal?>("AccountBalance"),
});
to that call:
var customers = query.ToList(() => new
{
Id = default(int),
Name = default(string),
Age = default(int),
BirthDate = default(DateTime?),
Bio = default(string),
AccountBalance = default(decimal?)
});
and do the DataReader.Get things from the new method, the first method is:
public List<T> ToList<T>(FluentSelectQuery query, Func<IDataReader, T> mapper)
{
return ToList<T>(mapper, query.ToString(), query.Parameters);
}
I had to build an expression in the new method:
public List<T> ToList<T>(Expression<Func<T>> type, string sql, params object[] parameters)
{
var expression = (NewExpression)type.Body;
var constructor = expression.Constructor;
var members = expression.Members.ToList();
var dataReaderParam = Expression.Parameter(typeof(IDataReader));
var arguments = members.Select(member =>
{
var memberName = Expression.Constant(member.Name);
return Expression.Call(typeof(Utilities),
"Get",
new Type[] { ((PropertyInfo)member).PropertyType },
dataReaderParam, memberName);
}
).ToArray();
var body = Expression.New(constructor, arguments);
var mapper = Expression.Lambda<Func<IDataReader, T>>(body, dataReaderParam);
return ToList<T>(mapper.Compile(), sql, parameters);
}
Doing this that way, i can completely avoid the Activator.CreateInstance or the FormatterServices.GetUninitializedObject stuff, I bet it's a lot faster ;)

Question #2:
I don't really know, but I would tend to use Activator.CreateObject() instead of FormatterServices.GetUninitializedObject(), because your object might not be created properly. GetUninitializedObject() won't run a default constructor like CreateObject() will, and you don't necessarily know what's in the black box of T...

This method stores one line of a sql query in a variable of anonymous type. You have to pass a prototype to the method. If any property of the anonymous type can not be found within the sql query, it is filled with the prototype-value. C# creates constructors for its anonymous classes, the parameters have the same names as the (read-only) properties.
public static T GetValuesAs<T>(this SqlDataReader Reader, T prototype)
{
System.Reflection.ConstructorInfo constructor = prototype.GetType().GetConstructors()[0];
object[] paramValues = constructor.GetParameters().Select(
p => { try { return Reader[p.Name]; }
catch (Exception) { return prototype.GetType().GetProperty(p.Name).GetValue(prototype); } }
).ToArray();
return (T)prototype.GetType().GetConstructors()[0].Invoke(paramValues);
}