We Keep Coding

System.MissingMethodException: Method not found: '?' when trying to build a custom dynamic type with a delegate method

I am trying to dynamically build a type with a method that calls into an external delegate by using System.Reflection.Emit. However when I try to call this method, my program crashes with the exception in the title at the method call. Here's my code so far:
private static void TestMethodReal() => Console.Out.WriteLine("Inside TestMethod");
// In Main()
var method = typeof(Program).GetMethod(nameof(TestMethodReal), BindingFlags.Static | BindingFlags.NonPublic)!;
var builder = MyTypeBuilder.GetTypeBuilder("TestType");
var testMethod = builder.DefineMethod("TestMethod", MethodAttributes.Public, typeof(void), Type.EmptyTypes);
var generator = testMethod.GetILGenerator();
generator.EmitCall(OpCodes.Callvirt, method, null);
generator.Emit(OpCodes.Ret);
dynamic inst = Activator.CreateInstance(builder.CreateType()!)!;
inst.TestMethod(); // <--- Exception is thrown here
The MyTypeBuilder class and GetTypeBuilder method is from this answer, slightly modified to accept a parameter for the type's name.
This program is supposed to create a new dynamic class with a method called TestMethod that calls the actual TestMethodReal method, instantiate the class, and call the method.
What am I missing?

You're using the wrong dispatch mechanism!
OpCodes.Callvirt is for virtual method calls, eg. overridable instance methods, the resolution of which needs to be deferred until runtime.
For static method invocation you'll want a plain old OpCodes.Call instruction instead:
generator.EmitCall(OpCodes.Call, method, Types.EmptyTypes);

Call a generic non-static method with dynamic type and generic callback as parameter

Developing an app for Android (and later iOS) using Xamarin/Mono. Normally I use this code to call a non-static generic method and it works great:
serverService.GetCustomListObject<T> (firstRequestInLine,
null,
onGetCustomListObjectFromThread<T>,
onGetCustomListObjectFromThreadError);
where the callbacks are defined as:
private void onGetCustomListObjectFromThread<T> (List<T> list,
RequestStateGen<T>.SuccessfullDelegateType successDel
{ ... }
and
private void onGetCustomListObjectFromThreadError (String error,
WebRequest failedRequest)
{ ... }
However, now I need to call GetCustomListObject<t> where t is set dynamically. I am quite new to generics but have tried the following code from other examples without success:
typeof(ServerService).GetMethod ("GetCustomListObject").MakeGenericMethod (t).Invoke (serverService, new object[] {
firstRequestInLine,
null,
typeof(LocalServerService).GetMethod ("onGetCustomListObjectFromThread").MakeGenericMethod (t),
typeof(LocalServerService).GetMethod ("onGetCustomListObjectFromThreadError")
});
where LocalServerService is the class all my examples here are in and serverService is of type ServerService
I get the following error:
Error: Ambiguous matching in method resolution
Edit: GetCustomListObject in ServerService:
public void GetCustomListObject<T> (WebRequest request,
RequestStateGen<T>.SuccessfullDelegateType successDelegate,
RequestStateGen<T>.InternalSuccessDelegateType internalSuccessDelegate,
RequestStateGen<T>.ErrorDelegateType errorDelegate)

In your original code, you were calling a method passing in delegates.
In your reflection code, you appear to be passing in MethodInfo values instead - I don't believe they will automatically be converted to delegates.
Unfortunately it's hard to give a good code sample without knowing the declaration of your GetCustomListObject method, but you want something like:
Type thirdArgType = typeof(Foo<>).MakeGenericGenericType(t);
MethodInfo thirdArgMethod = typeof(LocalServerService)
.GetMethod("onGetCustomListObjectFromThread",
BindingFlags.Instance | BindingFlags.NonPublic)
.MakeGenericMethod(t);
Delegate thirdArg = Delegate.CreateDelegate(thirdArgType, this, thirdArgMethod);
MethodInfo fourthArgMethod = typeof(LocalServerService)
.GetMethod("onGetCustomListObjectFromThreadError",
BindingFlags.Instance | BindingFlags.NonPublic);
Delegate fourthArg = Delegate.CreateDelegate(typeof(Bar), this, fourthArgMethod);
MethodInfo method = typeof(ServerService).GetMethod("GetCustomListObject")
.MakeGenericMethod (t);
method.Invoke(serverService,
new object[] {firstRequestInline, null, thirdArg, fourthArg });

Invoking Method on Object Instantiated From DLL

I am having some trouble with assemblies and DLL's.
instrument_ is declared as an object and I'm creating an instance of "PP150" from the dll whose path is specified by path_.
string className = ContineoProperties.getSingleton().getClassName(path_);
assembly_ = Assembly.LoadFrom(path_);
Type classType = assembly_.GetType("Instrument." + className);
instrument_ = Activator.CreateInstance(classType);
Later I to call the method isntrument_.instrumentCommand(cmd.getCommandName())
The error I get is with when i call the method.
'object' does not contain a definition for 'instrumentCommand'
The isntrument_ is created fine. its just the method call that's giving me a problem. The method does exist in the "PP150.dll". Do I need some DLLImport to allow it to recognize it as a function?
Thanks,
P

If object type is not known in compile time,
To call a method defined on an object, you must use Reflection.
MethodInfo mInfo = classType.GetMethod("instrumentCommand");
mInfo.Invoke(instrument_, new Object[] { _parameters});

The compiler is never going to recognize the methods on a type that you are loading via reflection (e.g. using Assembly.GetType() and Activator.CreateInstance()). Unless you have the type metadata available at build time, you will always get that error if you try to call methods that are not defined on Object itself.
You have two options for making that kind of method call. Both of them require you to give up type safety, the only difference is the amount of work required. In both cases, if you make a mistake, the compiler will not tell you -- you will get a runtime exception instead.
Declare instrument_ as dynamic instead of object. This, obviously, only works in .NET 4.0, but it accomplishes exactly what you're trying to do. The method call will be dispatched at runtime, so as long as the instance that instrument_ references actually has a method call with the appropriate name, it will work.
Use reflection to call the method. You're already using reflection to load the type, so you are halfway there. You would need to add something like this:
// The array of types is the parameter list; assuming instrumentCommand takes
// a string it would look like this:
MethodInfo method = classType.GetMethod("instrumentCommand", new Type[] { typeof(string) });
method.Invoke(instrument_, new object[] { cmd.getCommandName() });

This happens because Activator.CreateInstance returns an object. I would create a separate DLL for the interface which is implemented by the class you want to instantiate. Both the DLL containing this class, and the executable should reference the DLL containing the interface. This way you could cast the object returned by Activator.CreateInstance to the interface, and call its methods:
IInstrument.dll:
interface IInstrument
{
void instrumentCommand(string cmd);
}
Instrument.dll (add IInstrument.dll as reference):
class Instrument : IInstrument
{
public void instrumentCommand(string cmd)
{
// ... implementation ...
}
}
InstrumentApp.exe (add IInstrument.dll as reference):
class Program
{
public static void Main()
{
// ... load Instrument.dll into assembly object ...
// ... load the type from the assembly ...
IInstrument instrument_ = (IInstrument)Activator.CreateInstance(classType);
instrument_.instrumentCommand(cmd.getCommandName());
}
}

The most simple thing would be to link agains PP150.
If you did link against the dll you must use Assembly.LoadFile or Assembly.Load and not LoadFrom because the last one will cause the assembly load to load your assembly in the LoadFrom loader context which will alter type identity.
Suppose you load the Type T from Assembly A via LoadFrom and you link against A as well.
object CreateTypeFrom()
{
var A = Assembly.LoadFrom(#"xxxx");
return A.CreateInstance("T");
}
void Test()
{
object t = CreateTypeFrom();
T RealT = new T(); // no prob
T Castedt = (T)t; // this will throw an InvalidCastException
T isNull = t as T; // this will result in a null instance
}
As you can see although you did create two times an instance of T they cannot be casted to due to different loader context which will make the type pretty useless.
To get rid of these things you could simply use Reflection to create a proxy type which will forward your calls to the proxy type. If you are using .NET 4 you can take advantage of the DLR to find the best matching methods at runtime. The code below creats a Version object and returns it as dynamic object. Then I do call the Major property to an integer and print it out to console. This does work with no exceptions nor compile time errors if you are using .NET 4 or later.
dynamic CreateTypeFrom()
{
var assembly = typeof(string).Assembly;
return assembly.CreateInstance("System.Version", true, BindingFlags.CreateInstance, null, new object[] { 1, 2, 3, 4 }, null, null);
}
[TestMethod]
public void Test()
{
var t = CreateTypeFrom();
int major = t.Major;
Console.WriteLine(major);
}

Trying to use Reflection to Invoke Method within same class

I have a WCF service that accepts an object as a parameter that has a URI and Method Name.
What I am trying to do is have a method that will look # the URI, if it contains the words "localhost" it will use reflection and call a method, of the name that is passed in as a parameter, within the the same class, return a value and continue on.
public class Test
{
public GetStatResponse GetStat(GetStatRequest request)
{
GetStatResponse returnValue = new GetStatResponse();
if(Helpers.Contains(request.ServiceURI,"localhost", StringComparison.OrdinalIgnoreCase))
{
MethodInfo mi = this.GetType().GetMethod(request.ServiceMethod /*, BindingFlags.Public | BindingFlags.IgnoreCase*/);
returnValue = (GetStatResponse)mi.Invoke(this,null);
}
The above is the code segment pertaining to this question. I pull the MethodInfo no problem but I am running into issues on the mi.Invoke. The exception that I receive is "Exception has been thrown by the target of an invocation." With an Inner Exception "Object reference not set to an instance of an object". I have tried changing the code to (GetStatResponse)mi.Invoke(new Test(), null), with no luck. Test being the class.
I'm open to other suggestions as to how to resolve this, I just thought reflection might be the easiest.
The Method that I am calling with my testing is defined as
public GetStatResponse TestMethod()
{
GetStatResponse returnValue = new GetStatResponse();
Stat stat = new Stat();
Stat.Label = "This is my label";
Stat.ToolTip = "This is my tooltip";
Stat.Value = "this is my value";
returnValue.Stat = stat;
return returnValue;
}

Because you are not specifying BindingFlags in your GetMethod() call, you are only going to be returned methods matching the name containing request.ServiceMethod that are PUBLIC.
Check whether the method you are trying to invoke is public, otherwise MethodInfo will return null.
If it is not public, either make the method public or include the BindingFlags.NonPublic flag.
Also, you should always make sure that mi != null before calling mi.Invoke

Before calling the method you might want to make sure that the MethodInfo you are pulling through reflection is not null:
MethodInfo mi = this.GetType().GetMethod(
request.ServiceMethod,
BindingFlags.Public | BindingFlags.Instance | BindingFlags.IgnoreCase
);
// Make sure that the method exists before trying to call it
if (mi != null)
{
returnValue = (GetStatResponse)mi.Invoke(this, null);
}
After your update it seems that the exception is thrown inside the method you are calling:
GetStatResponse returnValue = new GetStatResponse();
// Don't forget to initialize returnValue.Stat before using it:
returnValue.Stat = new WhateverTheTypeIs();
returnValue.Stat.Label = "This is my label";

Object of type 'customObject' cannot be converted to type 'customObject'

I receive the following error when I invoke a custom object
"Object of type 'customObject' cannot be converted to type 'customObject'."
Following is the scenario when I am get this error:
I invoke a method in a dll dynamically.
Load an assembly
CreateInstance....
When calling MethodInfo.Invoke() passing int, string as a parameter for my method works fine => No exceptions are thrown.
But if I try and pass one of my own custom class objects as a parameter, then I get an ArgumentException exception, and it is not either an ArgumentOutOfRangeException or ArgumentNullException.
"Object of type 'customObject' cannot be converted to type 'customObject'."
I am doing this in a web application.
The class file containing the method is in a different project. Also the custom object is a separate class in the same file.
There is no such thing called a static assembly in my code. I am trying to invoke a webmethod dynamically. this webmethod is having the customObject type as an input parameter. So when i invoke the webmethod i am dynamically creating the proxy assembly and all. From the same assembly i am trying to create an instance of the cusotm object assinging the values to its properties and then passing this object as a parameter and invoking the method. everything is dynamic and nothing is created static.. :(
add reference is not used.
Following is a sample code i tried to create it
public static object CallWebService(string webServiceAsmxUrl, string serviceName, string methodName, object[] args)
{
System.Net.WebClient client = new System.Net.WebClient();
//-Connect To the web service
using (System.IO.Stream stream = client.OpenRead(webServiceAsmxUrl + "?wsdl"))
{
//--Now read the WSDL file describing a service.
ServiceDescription description = ServiceDescription.Read(stream);
///// LOAD THE DOM /////////
//--Initialize a service description importer.
ServiceDescriptionImporter importer = new ServiceDescriptionImporter();
importer.ProtocolName = "Soap12"; // Use SOAP 1.2.
importer.AddServiceDescription(description, null, null);
//--Generate a proxy client. importer.Style = ServiceDescriptionImportStyle.Client;
//--Generate properties to represent primitive values.
importer.CodeGenerationOptions = System.Xml.Serialization.CodeGenerationOptions.GenerateProperties;
//--Initialize a Code-DOM tree into which we will import the service.
CodeNamespace nmspace = new CodeNamespace();
CodeCompileUnit unit1 = new CodeCompileUnit();
unit1.Namespaces.Add(nmspace);
//--Import the service into the Code-DOM tree. This creates proxy code
//--that uses the service.
ServiceDescriptionImportWarnings warning = importer.Import(nmspace, unit1);
if (warning == 0) //--If zero then we are good to go
{
//--Generate the proxy code
CodeDomProvider provider1 = CodeDomProvider.CreateProvider("CSharp");
//--Compile the assembly proxy with the appropriate references
string[] assemblyReferences = new string[5] { "System.dll", "System.Web.Services.dll", "System.Web.dll", "System.Xml.dll", "System.Data.dll" };
CompilerParameters parms = new CompilerParameters(assemblyReferences);
CompilerResults results = provider1.CompileAssemblyFromDom(parms, unit1);
//-Check For Errors
if (results.Errors.Count > 0)
{
StringBuilder sb = new StringBuilder();
foreach (CompilerError oops in results.Errors)
{
sb.AppendLine("========Compiler error============");
sb.AppendLine(oops.ErrorText);
}
throw new System.ApplicationException("Compile Error Occured calling webservice. " + sb.ToString());
}
//--Finally, Invoke the web service method
Type foundType = null;
Type[] types = results.CompiledAssembly.GetTypes();
foreach (Type type in types)
{
if (type.BaseType == typeof(System.Web.Services.Protocols.SoapHttpClientProtocol))
{
Console.WriteLine(type.ToString());
foundType = type;
}
}
object wsvcClass = results.CompiledAssembly.CreateInstance(foundType.ToString());
MethodInfo mi = wsvcClass.GetType().GetMethod(methodName);
return mi.Invoke(wsvcClass, args);
}
else
{
return null;
}
}
}
I can't find anything static in what I do.
Any help is greatly appreciated.
Regards,
Phani Kumar PV

Have you looked at what the proxy class looks like that gets generated? You don't need the proxy to call a web service. Just create a class that inherits from SoapHttpClientProtocol and call Invoke(methodName, params).
You are making this SO much more complicated than you need to. Honestly.
EDIT
If you create a class like this:
public class SoapClient : SoapHttpClientProtocol
{
public SoapClient()
{
}
public object[] Invoke(string method, object[] args)
{
return base.Invoke(method, args);
}
}
and call it like this:
SoapClient soapClient = new SoapClient();
soapClient.Url = webServiceAsmxUrl;
soapClient.Invoke(methodName, args);
I think you will see that it has the exact same results as what you are doing.

Let me try to explain the most probable reason for the problem to come in my approach.
When I invoked a method in the assembly called as "methodname" in the webservice I am trying to pass the parameters required for that as args[] to the function "CallWebService"
This args[] when passed will be successfully working when I try to pass a normal parameters like primitive types including string.
But this is what I did when I tried to pass a custom object as a parameter.
Three things that are done in this.
create an object of that type outside the CallWebService function (using reflection). when I did that way what happens is an instance of the customobject created with a temporary dll name internally.
once I set the set the properties of the object and send it across to the CallWebService function as an object in the args array.
I tired to create an instance of the webservice by creating the dynamic dll.
object wsvcClass = results.CompiledAssembly.CreateInstance(foundType.ToString());
When I finally tried to invoke the method with the instance of the dynamic assembly created
I tried to pass the customobject that is created at step 1,2 via args property.
at the time of invocation the CLR tries to see if the customobject that is passed as input and the method that is being invoked are from the same DLL.
which is obviously not from the way the implementation is done.
So following is the approach that should be used to overcome the problem
I need to create the custom object assembly with the same assembly that I used to the create the webservice instance..
I implemented this approach completely and it worked out fine
MethodInfo m = type.GetMethod(methodName);
ParameterInfo[] pm = m.GetParameters();
object ob;
object[] y = new object[1];
foreach (ParameterInfo paraminfo in pm)
{
ob = this.webServiceAssembly.CreateInstance(paraminfo.ParameterType.Name);
//Some Junk Logic to get the set the values to the properties of the custom Object
foreach (PropertyInfo propera in ob.GetType().GetProperties())
{
if (propera.Name == "AppGroupid")
{
propera.SetValue(ob, "SQL2005Tools", null);
}
if (propera.Name == "Appid")
{
propera.SetValue(ob, "%", null);
}
}
y[0] = ob;
}

this can occur when the version of a dll you have referenced in your reflected code is different from the version of that dll in your compiled code.

This is an old thread, but I just had a similar problem. I looked on here, this one popped up, but I saw no useful solutions.
The OP's error was this: Object of type 'customObject' cannot be converted to type 'customObject'.
My very similar error was this: Object of type 'System.String' cannot be converted to type 'System.Windows.Forms.AccessibleRole'.
Here is how I solved my problem:
I performed a Find and Replace (use CRTL+SHIFT+F to bring the dialog box up) search in the Current Project for the term AccessibleRole.
Within one of the Form's Designer's was a place where I was assigning an AccessibleRole value to a String variable using ToString().
I fixed this, and my problem went away.
I hope this provides help to others.