获取扩展方法的 MethodInfo

Question

I cant get the method info for an extension method as I would suspect. Whats wrong?

_toStringMethod = typeof(ObjectExtensions).GetMethod("TryToString",
    BindingFlags.Public | BindingFlags.Static);

Answer 1

Works for me:

using System;
using System.Reflection;

public static class ObjectExtensions
{
    public static string TryToString(this object x)
    {
        // Just guessing...
        return x == null ? "" : x.ToString();
    }
}

class Test
{
    static void Main()
    {
        var method = typeof(ObjectExtensions).GetMethod(
            nameof(ObjectExtensions.TryToString),
            BindingFlags.Public | BindingFlags.Static);
        // Prints System.String TryToString(System.Object)
        Console.WriteLine(method);
    }
}

Can you give a similar short but complete example which fails?

Answer 2

Works for me. Just check that your method class, name, and modifier are all correct.

As a note, there is no reason that it shouldn't work under any circumstances. Extension methods are still "normal" methods in that they belong to the static class in which the defined. It is only the way you access them that differs (though you can still access them normally too, of course).

Answer 3

I was unable to get the extension method on my code too It was just a namespace conflict of me which instead of my Extension class It was using EntityFramework's Extension class so I have to explicitly type it

typeof(MyAppNamespace.Extensions).GetMethod(...)

instead of:

typeof(Extensions).GetMethod(...)

Answer 4

For those who don't want to call GetMethod on the Extension class, there is only one way at the moment. You should get all the Types in the namespace which have ExtensionAttribute (This attribute is given to extension classes and methods in compile time automatically.)

Type[] allTypes = Assembly.GetEntryAssembly().GetTypes();
Type[] extensionTypes = allTypes.Where(t => t.IsDefined(typeof(ExtensionAttribute))).ToArray();

Then we'll get the methods which have ExtensionAttribute .

MethodInfo[] extensionMethods = extensionTypes.SelectMany(e => e.GetMethods().Where(m => m.IsDefined(typeof(ExtensionAttribute)))).ToArray();

So, the result of extensionMethods will be all the extension methods in the namespace. We only need the ones that their first parameter is of our selected type.

MethodInfo[] matchExtensionMethods = extensionMethods.Where(m => m.GetParameters()[0].ParameterType == typeof(MyType)).ToArray();

Now you have an array of all the extension methods for your chosen type, you can find the proper method by its name.
Full code:

Type targetType = typeof(MyClass);
MyClass targetObject = new MyClass();
Type[] allTypes = Assembly.GetEntryAssembly().GetTypes();
Type[] extensionTypes = allTypes.Where(t => t.IsDefined(typeof(ExtensionAttribute))).ToArray();
MethodInfo[] extensionMethods = extensionTypes.SelectMany(e => e.GetMethods().Where(m => m.IsDefined(typeof(ExtensionAttribute)))).ToArray();
MethodInfo[] matchExtensionMethods = extensionMethods.Where(m => m.GetParameters()[0].ParameterType == targetType).ToArray();
matchExtensionMethods.First(m => m.Name == "TryToString").Invoke(null, targetObject);

Please note that we're invoking with null passed as the object, because the method is static.