How Can I Safely Select the Correct Generic Method Overload Using Reflection in C#?

Use reflection to choose the correct generic method

When using generic methods via reflection, choosing the correct overload can be challenging when there are multiple generic overloads. This problem occurs when the method name is ambiguous, such as the "Where" method in the System.Linq.Queryable class.

Instead of relying on assumptions or checking method names, there is a compile-time safe way to select the correct generic overload using delegates.

Static method

Consider the following static method with multiple generic overloads:

<code class="language-csharp">public static void DoSomething<TModel>(TModel model)

public static void DoSomething<TViewModel, TModel>(TViewModel viewModel, TModel model)</code>

To select the first overload (void return type, one generic parameter), create an operation delegate matching its signature:

<code class="language-csharp">var method = new Action<object>(MyClass.DoSomething<object>);</code>

For the second overload (void return type, two generic parameters), use an action delegate with two object parameters:

<code class="language-csharp">var method = new Action<object, object>(MyClass.DoSomething<object, object>);</code>

This method selects the correct overload based on the delegate's generic count and argument count.

To obtain a MethodInfo object, use the delegate's Method property and call MakeGenericMethod():

<code class="language-csharp">var methodInfo = method.Method.MakeGenericMethod(type1, type2);</code>

Static extension method

For instance methods, use a similar method select method, but call GetGenericMethodDefinition() before passing the type to MakeGenericMethod():

<code class="language-csharp">var methodInfo = method.Method.GetGenericMethodDefinition().MakeGenericMethod(type1);</code>

Decoupling MethodInfo and parameter types

You can get a generic MethodInfo object by calling GetGenericMethodDefinition(), thereby decoupling the selection of MethodInfo objects from the parameter types:

<code class="language-csharp">var methodInfo = method.Method.GetGenericMethodDefinition();</code>

Then, pass the necessary types to MakeGenericMethod() when calling the method:

<code class="language-csharp">processCollection(methodInfo, type2);

...

protected void processCollection(MethodInfo method, Type type2)
{
    var type1 = typeof(MyDataClass);
    object output = method.MakeGenericMethod(type1, type2).Invoke(null, new object[] { collection });
}</code>

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