How do I use reflection to invoke a private method in C#?

Question

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?

Answer 1

BindingFlags.NonPublic

Answer 2

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

Answer 3

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.

Answer 4

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.

~ William Riley-Land

Answer 5

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);

Answer 6

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.

Answer 7

I am getting a ambigiousMatchException for my code below:

Can anybody tell me whats wrong with this?

Type myType = new String(new char[] {'b','a','l','a','j','i'}).GetType(); string[] operations = new string[] { "ToUpper","Trim"};

    foreach (string operation in operations)
    {
        Response.Write("\n" + operation + "  " + myType.GetMethod(operation).Invoke(this,null)); 

    }

Thanks in advance