[DllImport("user32.dll")]

public static extern IntPtr FindWindow(string className, string windowName);

[DllImport("user32.dll")]

internal static extern IntPtr SetForegroundWindow(IntPtr hWnd);

[DllImport("user32.dll")]

internal static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);

private void GetFocusWin() {

    // get hWnd, nb. hWnd always seems to return 0 with this method

    // http://stackoverflow.com/questions/7357675/how-can-i-set-the-focus-to-application-which-is-allready-in-running-state?rq=1

    //System.Diagnostics.Process currentProcess = System.Diagnostics.Process.GetCurrentProcess();

    //IntPtr hWnd = currentProcess.MainWindowHandle;

    // get hWnd, nb. this works ok on Windows 7 x64

    // http://ronniediaz.com/2011/05/03/start-a-process-in-the-foreground-in-c-net-without-appactivate/

    IntPtr hWnd = FindWindow(null, "Your App Name");

    if (hWnd != IntPtr.Zero) {

        Debug.Log("GetFocusWin() setting foreground window, showing window SW_SHOWDEFAULT");

        SetForegroundWindow(hWnd);

        // enum values from https://msdn.microsoft.com/en-us/library/windows/desktop/ms633548(v=vs.85).aspx

        ShowWindow(hWnd, 10); // SW_SHOWDEFAULT = 10, SW_MAXIMIZE = 3, SW_SHOW = 5

    } else {

        Debug.LogWarning("GetFocusWin() failed, hWnd is 0!");

    }

}