CODEWITHSUNDEEP
c#.net-4.0sendmessagepostmessage
Zoetyc
Zoetyc

Reputation: 67

Postmessage not being sent until window receives focus. C# .NET

I'm trying to Postmessage send key inputs to an application. The issue is that the message is being sent only when the application becomes active or gains focus.

Here is my goal: I need the application to receive inputs either while it is not focused, or via some pseudo-focus called via postmessage before the input is sent (I have tried: NativeMethods.PostMessage(mainHwnd, 0x0007, 0, 0); "0x0007" is WM_SETFOCUS but this doesn't do anything). Any assistance would be very helpful, I've been at this for more hours than I care to count.🙏

Here is all of the relevant code I'm using:

using System.Runtime.InteropServices;
using System;
using System.Windows.Forms;
using System.Threading;

internal static class NativeMethods
{
    [DllImport("user32.dll", SetLastError = true)]
    public static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

    [DllImport("user32.dll", SetLastError = true)]
    public static extern IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfter, string lpszClass, string lpszWindow);

    [return: MarshalAs(UnmanagedType.Bool)]
    [DllImport("user32.dll", SetLastError = true)]
    public static extern bool PostMessage(IntPtr hWnd, UInt32 Msg, Int32 wParam, Int32 lParam);

    [DllImport("User32.dll")]
    public static extern int SendMessage(IntPtr hWnd, UInt32 uMsg, Int32 wParam, Int32 lParam);
}

class Test
{
    const int WM_KEYDOWN = 0x0100;
    const int WM_KEYUP = 0x0101;
    //const int WM_SETFOCUS = 0x0007;

    [DllImport("user32.dll")]
    public static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, int wParam, int lParam);

    public static void SendKey()
    {
        IntPtr mainHwnd = NativeMethods.FindWindow(null, "Test Application");
        NativeMethods.PostMessage(mainHwnd, WM_KEYDOWN, (int)Keys.A, 0);
        Thread.Sleep(50);
        NativeMethods.PostMessage(mainHwnd, WM_KEYUP, (int)Keys.A, 0);
    }
}

class TryTheThing{
    public void Send() {
        Test.SendKey();
    }
}

Upvotes: 1

Views: 1296

Answers (1)

Visual Vincent
Visual Vincent

Reputation: 18320

Windows does not allow you to send keystrokes to non-focused applications. Your only option is to force the window to be focused first. This can be achieved by P/Invoking SetForegroundWindow():

[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool SetForegroundWindow(IntPtr hWnd);

NativeMethods.SetForegroundWindow(mainHwnd);

Upvotes: 1

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