C＃：FindWindowEx无法按预期工作

Question

Ok first off I'm new to C# so this may be something really simple, I've just not found the answer throughout Google/SO.

I have a class where I'm trying to use FindWindowEx, however, Visual Studio isn't allowing me to use 'null' arguments and I'm unsure why.

So far the class has this code:

    [DllImport("user32.dll")]
    public static extern IntPtr FindWindowEx(IntPtr handleParent, IntPtr handleChild, string className, string WindowName);

    [DllImport("user32.dll")]
    public static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);

    public void SomeWindow()
    {

        String someHwnd = FindWindowEx(IntPtr.Zero, IntPtr.Zero, "SomeWindowClass", NULL);

    }

As it is written, it is telling me that 'NULL' doesn't exist in the current context. I've also tried writing as:

FindWindowEx(null, null, "SomeWindowClass", null)

This gives errors under the first two 'null's saying "Argument #: Cannot convert from 'null' to 'IntPtr'" (The 'null' actually has < and > surrounding it although SO isn't displaying it with them)

The Windows Dev Center says I should be able to use it as I am though which is here: https://msdn.microsoft.com/en-us/library/windows/desktop/ms633500(v=vs.85).aspx

Like I said it may be something incredibly simple, I just don't have enough experience in C# to figure it out.

Answer 1

FindWindow return type is IntPtr, whereas you are trying to assign it to string.

Try this.

IntPtr wnd = FindWindowEx(IntPtr.Zero, IntPtr.Zero, "SomeWindowClass", null);