How do I use reflection to invoke a private method?

Jeromy_Irvine_8223 0
Viewed 203965

There are a group of private methods in my class, and I need to call one dynamically based on an input value. Both the invoking code and the target methods are in the same instance. The code looks like this:

MethodInfo dynMethod = this.GetType().GetMethod("Draw_" + itemType);
dynMethod.Invoke(this, new object[] { methodParams });

In this case, GetMethod() will not return private methods. What BindingFlags do I need to supply to GetMethod() so that it can locate private methods?

private-methods reflection .net c#
11 Answers

Simply change your code to use the overloaded version of GetMethod that accepts BindingFlags:

MethodInfo dynMethod = this.GetType().GetMethod("Draw_" + itemType, 
    BindingFlags.NonPublic | BindingFlags.Instance);
dynMethod.Invoke(this, new object[] { methodParams });

Here's the BindingFlags enumeration documentation.

user_178470

BindingFlags.NonPublic will not return any results by itself. As it turns out, combining it with BindingFlags.Instance does the trick.

MethodInfo dynMethod = this.GetType().GetMethod("Draw_" + itemType, 
    BindingFlags.NonPublic | BindingFlags.Instance);
Jeromy_Irvine_82230

Are you absolutely sure this can't be done through inheritance? Reflection is the very last thing you should look at when solving a problem, it makes refactoring, understanding your code, and any automated analysis more difficult.

It looks like you should just have a DrawItem1, DrawItem2, etc class that override your dynMethod.

Bill_K_129430

Could you not just have a different Draw method for each type that you want to Draw? Then call the overloaded Draw method passing in the object of type itemType to be drawn.

Your question does not make it clear whether itemType genuinely refers to objects of differing types.

Peter_Hession_4410

Invokes any method despite its protection level on object instance. Enjoy!

public static object InvokeMethod(object obj, string methodName, params object[] methodParams)
{
    var methodParamTypes = methodParams?.Select(p => p.GetType()).ToArray() ?? new Type[] { };
    var bindingFlags = BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance | BindingFlags.Static;
    MethodInfo method = null;
    var type = obj.GetType();
    while (method == null && type != null)
    {
        method = type.GetMethod(methodName, bindingFlags, Type.DefaultBinder, methodParamTypes, null);
        type = type.BaseType;
    }

    return method?.Invoke(obj, methodParams);
}
user_8367230

I think you can pass it BindingFlags.NonPublic where it is the GetMethod method.

Armin_Ronacher_199900

It should be noted that calling from a derived class can be problematic.

Error prone:

this.GetType().GetMethod("PrivateTestMethod", BindingFlags.Instance | BindingFlags.NonPublic)

Correct:

typeof(CurrentClass).GetMethod("PrivateTestMethod", BindingFlags.Instance | BindingFlags.NonPublic)
user_157759930

Read this (supplementary) answer (that is sometimes the answer) to understand where this is going and why some people in this thread complain that "it is still not working"

I wrote exactly same code as one of the answers here. But I still had an issue. I placed break point on 

var mi = o.GetType().GetMethod(methodName, BindingFlags.NonPublic | BindingFlags.Instance );

It executed but mi == null

And it continued behavior like this until I did "re-build" on all projects involved. I was unit testing one assembly while the reflection method was sitting in third assembly. It was totally confusing but I used Immediate Window to discover methods and I found that a private method I tried to unit test had old name (I renamed it). This told me that old assembly or PDB is still out there even if unit test project builds - for some reason project it tests didn't built. "rebuild" worked

user_17044580
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