PrivateObject ignoring integer argument if it is 0

Question

I ran into a strange problem with PrivateObject that seems to ignore an integer argument given to the Invoke call if the value is "0". See the basic example below:

using System;
using System.Reflection;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace TestProject1
{
    [TestClass]
    public class UnitTest1
    {
        [TestMethod]
        public void TestMethod1()
        {
            var sut = new MyClass();
            var sutPrivate = new PrivateObject(sut);

            // Passes:
            Assert.AreEqual(1, (int)sutPrivate.Invoke("MyMethod", 1));

            // MissingMethodException:
            Assert.AreEqual(0, (int)sutPrivate.Invoke("MyMethod", 0));
            // MissingMethodException:
            Assert.AreEqual(0, (int)sutPrivate.Invoke("MyMethod", new [] {typeof(UInt32)}, 0));

            // Passes!
            Assert.AreEqual(0, (int)sutPrivate.Invoke("MyMethod", BindingFlags.NonPublic | BindingFlags.Instance, 0));
        }
    }

    internal class MyClass
    {
        private int MyMethod(int arg)
        {
            return arg;
        }
    }
}

Note that the first invoke works as expected because the integer argument is "1". Second one fails with MissingMethodException and it doesn't even help to specify a type array as is done in the third attempt. Strangely it helps to specify BindingFlags.NonPublic and BindingFlags.Instance, which should be giving by using PrivateObject. Looking at the IL code I can see that the compiler omits the argument completely so MissingMethodException happens for a reason.

This seems like an error in the Invoke overload on PrivateObject or in the underlaying reflection calls, or have I missed something?

---

Tore Østergaard
Oticon A/S, Denmark

Answer 1

Hi Tore,

Thank you for posting in the MSDN forum.

I try to repro this issue. Then I use the tool .NET Reflector to check it

1)Assert.AreEqual(0, (int)sutPrivate.Invoke("MyMethod", (object)0));

Result: Failed

I get the result like the following screen shot with that tool.

2)Assert.AreEqual(1, (int)sutPrivate.Invoke("MyMethod", 1));

See:

Result: Passed

3)Assert.AreEqual(0, (int)sutPrivate.Invoke("MyMethod", (object)0));

Result: Passed

4)int i = 0;

  Assert.AreEqual(0, sutPrivate.Invoke("MyMethod", i));

Result: Passed

As my understanding that if we use the step1 with 0, we just get an array like the object[0],  it has the return value, but it could be the int or double or others, I think it is related to the Boxing and Unboxing, see http://msdn.microsoft.com/en-us/library/yz2be5wk(v=vs.100).aspx.

So if possible, use the workaround provided by us, hope it helps.

Best Regards,

---

Jack Zhai [MSFT]
MSDN Community Support | Feedback to us

Answer 2

Thank you for your reply Jack.

Your solution 4 does indeed work, but put a "const" keyword in front of the declaration of the i variable (which Resharper will help you remember) and you get back into the MissingMethodException.

I think that I will use the boxing workaround, but I still think that it is a bug somewhere in the framework since I can work around it by using another overload to the Invoke method.

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Tore Østergaard
Oticon A/S, Denmark

Answer 3

Hi Tore,

Glad to receive your reply.J

As my understanding, it is related to the Boxing and Unboxing. But if you think it is a feedback, you can submit this feedback to Microsoft Connect feedback portal: http://connect.microsoft.com, Microsoft engineers will evaluate them seriously. Thanks for your understanding.

Best Regards,

---

Jack Zhai [MSFT]
MSDN Community Support | Feedback to us

Answer 4

I have created a Microsoft Connect feedback ticket: http://connect.microsoft.com/VisualStudio/feedback/details/732374/zero-integer-argument-is-seen-as-empty-array

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Tore Østergaard
Oticon A/S, Denmark