CODEWITHSUNDEEP
c#winapiinteroppinvoke
denver
denver

Reputation: 3135

GetAsyncKeyState DLLImport statement

I ran into a situation where I needed to change the DLL Import statement I was using depending on the OS. I'm wondering if anyone else has observed this, knows why, or if there is a better way to handle this.

Here is a minimal code snippet showing the problem. It is a simple command line app that just outputs the status of the shift key.

using System;
using System.Runtime.InteropServices;

namespace Shift
{
    class Program
    {
        [DllImport("user32.dll", SetLastError = true)]
        public static extern short GetAsyncKeyState(ushort virtualKeyCode);

        static void Main(string[] args)
        {
            Console.WriteLine("Shift is: " + GetAsyncKeyState(0x10));
        }
    }
}

The above works fine for me when ran on Windows 8.1 x64 or when built as 32-bits and run on Windows 7 x64. It does not however work on a Windows 7 system when compiled for x64. In that case GetAsyncKeyState always returns 0.

If I change the DLLImport to the following it then works on Windows 7 system when compiled for x64.

[DllImport("user32.dll", SetLastError = true)]
public static extern short GetAsyncKeyState(int virtualKeyCode);

Upvotes: 2

Views: 2209

Answers (1)

David Heffernan
David Heffernan

Reputation: 612963

The original declaration is wrong. The documentation is here: https://msdn.microsoft.com/en-us/library/windows/desktop/ms646293.aspx

This gives the declaration as:

SHORT WINAPI GetAsyncKeyState(
  _In_ int vKey
);

The correct p/invoke is:

[DllImport("user32.dll")]
public static extern short GetAsyncKeyState(int vKey);

Note that I have removed the setting of SetLastError. The documentation makes no mention of SetLastError being called.

Upvotes: 3

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