CODEWITHSUNDEEP
c#reflectiondelegates
Ty.
Ty.

Reputation: 3948

Getting a delegate from methodinfo

I have a drop down list that is populated by inspecting a class's methods and including those that match a specific signature. The problem is in taking the selected item from the list and getting the delegate to call that method in the class. The first method works, but I cannot figure out part of the second.

For example,

public delegate void MyDelegate(MyState state);

public static MyDelegate GetMyDelegateFromString(string methodName)
{
    switch (methodName)
    {
        case "CallMethodOne":
            return MyFunctionsClass.CallMethodOne;
        case "CallMethodTwo":
            return MyFunctionsClass.CallMethodTwo;
        default:
            return MyFunctionsClass.CallMethodOne;
    }
}

public static MyDelegate GetMyDelegateFromStringReflection(string methodName)
{
    MyDelegate function = MyFunctionsClass.CallMethodOne;

    Type inf = typeof(MyFunctionsClass);
    foreach (var method in inf.GetMethods())
    {
        if (method.Name == methodName)
        {
            //function = method;
            //how do I get the function to call?
        }
    }

    return function;
}

How do I get the commented out section of the second method to work? How do I cast the MethodInfo into the delegate?

Thanks!

Edit: Here is the working solution.

public static MyDelegate GetMyDelegateFromStringReflection(string methodName)
{
    MyDelegate function = MyFunctionsClass.CallMethodOne;

    Type inf = typeof(MyFunctionsClass);
    foreach (var method in inf.GetMethods())
    {
        if (method.Name == methodName)
        {
            function = (MyDelegate)Delegate.CreateDelegate(typeof(MyDelegate), method);
        }
    }

    return function;
}

Upvotes: 54

Views: 34219

Answers (3)

Anders Carstensen
Anders Carstensen

Reputation: 4124

Here is a simpler version of Sagi's solution using Expression.GetDelegateType() instead of manually detecting whether an Action or Func is needed:

public static Delegate CreateDelegate(this MethodInfo methodInfo, object target)
{
    var parmTypes = methodInfo.GetParameters().Select(parm => parm.ParameterType);
    var parmAndReturnTypes = parmTypes.Append(methodInfo.ReturnType).ToArray();
    var delegateType = Expression.GetDelegateType(parmAndReturnTypes);

    if (methodInfo.IsStatic)
        return methodInfo.CreateDelegate(delegateType);
    return methodInfo.CreateDelegate(delegateType, target);
}

Upvotes: 2

Sagi
Sagi

Reputation: 9284

public static Delegate CreateDelegate(this MethodInfo methodInfo, object target) {
    Func<Type[], Type> getType;
    var isAction = methodInfo.ReturnType.Equals((typeof(void)));
    var types = methodInfo.GetParameters().Select(p => p.ParameterType);

    if (isAction) {
        getType = Expression.GetActionType;
    }
    else {
        getType = Expression.GetFuncType;
        types = types.Concat(new[] { methodInfo.ReturnType });
    }

    if (methodInfo.IsStatic) {
        return Delegate.CreateDelegate(getType(types.ToArray()), methodInfo);
    }

    return Delegate.CreateDelegate(getType(types.ToArray()), target, methodInfo.Name);
}

Upvotes: 35

Nate Kohari
Nate Kohari

Reputation: 2224

You'll need to call some form of Delegate.CreateDelegate(), depending on whether the method in question is a static or instance method.

Upvotes: 25

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