c# focus window of a runing program

Question

i want to focus a program from my c# application.i searched lot and found some examples.but i got error .i'm using visual studio.ShowWindow(hWnd, SW_HIDE); line gives me an error "showwindow(system.IntPtr,int) has some invalid argument" plz where is the problem of this code

[DllImport("user32.dll")]
        internal static extern IntPtr SetForegroundWindow(IntPtr hWnd);

        [DllImport("user32.dll")]
        internal static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);

 private void FocusProcess()
        {
            int hWnd;
            Process[] processRunning = Process.GetProcesses();
            foreach (Process pr in processRunning)
            {
                if (pr.ProcessName == "notepad")
                {
                    hWnd = pr.MainWindowHandle.ToInt32();
                    ShowWindow(hWnd, 3);//error line
                }
            }
        }

Why have you called `ToInt32()`? `MainWindowHandle` already gives you a value with the correct type. The type conversion is the reason you're getting an error: it is an incompatible type. — Cody Gray - on strike, Aug 30 '14 at 03:31

score 3 · Answer 1 · edited Oct 07 '19 at 13:46

You declared hWnd as int. But the ShowWindow function needs an IntPtr. Because pr.MainWindowHandle is an IntPtr you just need to use it as hWnd. Btw. if you want this window as the topmost you should call SetForegroundWindow.

    [DllImport("user32.dll")]
    internal static extern IntPtr SetForegroundWindow(IntPtr hWnd);

    [DllImport("user32.dll")]
    internal static extern bool ShowWindow(IntPtr hWnd, int nCmdShow); //ShowWindow needs an IntPtr

    private static void FocusProcess()
    {
        IntPtr hWnd; //change this to IntPtr
        Process[] processRunning = Process.GetProcesses();
        foreach (Process pr in processRunning)
        {
            if (pr.ProcessName == "notepad")
            {
                hWnd = pr.MainWindowHandle; //use it as IntPtr not int
                ShowWindow(hWnd, 3);
                SetForegroundWindow(hWnd); //set to topmost
            }
        }
    }

"Notepad" may need to be spelled with a capital N? Or maybe better use some case-insensitive comparison? — RenniePet, Aug 30 '14 at 02:58

c# focus window of a runing program

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