title: Need to activate a window
body: <p>I have a situation like this.
  I have the window handle of an application. I need to activate it. I tried all these functions but is not working always.(most of the time , it doesn't work the first time and I'll have to manually click on it to activate it. Second attempt onwards it works fine) 
  The reason why I am doing this is because I have code written in the Form.Activate event of the form which I need to execute.
  Application is a single instance application. When a new instance is created , it first checks for the existence of any other process, If found, the handle of old process is passed to the these functions so that user can work on the old form.
  Application is called from a different C application.
          [DllImport("user32.dll")]
          public static extern int ShowWindow(IntPtr hWnd, int nCmdShow);</p>
  
  <pre><code>    [DllImport("user32.dll")]
      public static extern int SetForegroundWindow(IntPtr hWnd);
  
      [DllImport("user32")]
      public static extern bool PostMessage(IntPtr hwnd, int msg, IntPtr wparam, IntPtr lparam);
  </code></pre>