2018年01月聚合问答--Reflection: How to Invoke Method with parameters

I am trying to invoke a method via reflection with parameters and I get:

object does not match target type

If I invoke a method without parameters, it works fine. Based on the following code if I call the method Test("TestNoParameters"), it works fine. However if I call Test("Run"), I get an exception. Is something wrong with my code?

My initial purpose was to pass an array of objects e.g. public void Run(object[] options) but this did not work and I tried something simpler e.g. string without success.

// Assembly1.dll
namespace TestAssembly
{
    public class Main
    {
        public void Run(string parameters)
        { 
            // Do something... 
        }
        public void TestNoParameters()
        {
            // Do something... 
        }
    }
}

// Executing Assembly.exe
public class TestReflection
{
    public void Test(string methodName)
    {
        Assembly assembly = Assembly.LoadFile("...Assembly1.dll");
        Type type = assembly.GetType("TestAssembly.Main");

        if (type != null)
        {
            MethodInfo methodInfo = type.GetMethod(methodName);

            if (methodInfo != null)
            {
                object result = null;
                ParameterInfo[] parameters = methodInfo.GetParameters();
                object classInstance = Activator.CreateInstance(type, null);

                if (parameters.Length == 0)
                {
                    // This works fine
                    result = methodInfo.Invoke(classInstance, null);
                }
                else
                {
                    object[] parametersArray = new object[] { "Hello" };

                    // The invoke does NOT work;
                    // it throws "Object does not match target type"             
                    result = methodInfo.Invoke(methodInfo, parametersArray);
                }
            }
        }
    }
}

5个回答

180

Change "methodInfo" to "classInstance", just like in the call with the null parameter array.

  result = methodInfo.Invoke(classInstance, parametersArray);

You have a bug right there

result = methodInfo.Invoke(methodInfo, parametersArray);

it should be

result = methodInfo.Invoke(classInstance, parametersArray);

A fundamental mistake is here:

result = methodInfo.Invoke(methodInfo, parametersArray);

You are invoking the method on an instance of MethodInfo. You need to pass in an instance of the type of object that you want to invoke on.

result = methodInfo.Invoke(classInstance, parametersArray);

The provided solution does not work for instances of types loaded from a remote assembly. To do that, here is a solution that works in all situations, which involves an explicit type re-mapping of the type returned through the CreateInstance call.

This is how I need to create my classInstance, as it was located in a remote assembly.

// sample of my CreateInstance call with an explicit assembly reference
object classInstance = Activator.CreateInstance(assemblyName, type.FullName);

However, even with the answer provided above, you'd still get the same error. Here is how to go about:

// first, create a handle instead of the actual object
ObjectHandle classInstanceHandle = Activator.CreateInstance(assemblyName, type.FullName);
// unwrap the real slim-shady
object classInstance = classInstanceHandle.Unwrap(); 
// re-map the type to that of the object we retrieved
type = classInstace.GetType();

Then do as the other users mentioned here.

I would use it like this, its way shorter and it won't give any problems

        dynamic result = null;
        if (methodInfo != null)
        {
            ParameterInfo[] parameters = methodInfo.GetParameters();
            object classInstance = Activator.CreateInstance(type, null);
            result = methodInfo.Invoke(classInstance, parameters.Length == 0 ? null : parametersArray);
        }

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[聚合问答] Reflection: How to Invoke Method with parameters

5个回答