HowTo: use a Timer component for delayed execution in WinForms

This is my contribution to:

http://stackoverflow.com/questions/303116/system-windows-threading-dispatcher-and-winforms

Sometimes a Timer component is useful and easy to setup in WinForms, just set its interval and then enable it, then make sure the first thing you do in its Tick event handler is to disable itself.

I think Timer runs the code in its own thread, so you may still need to do a BeginInvoke (called upon the WinForm object [this]) to run your Action.

 

private WebBrowserDocumentCompletedEventHandler handler;
//need to make it a class field for the handler below
//(anonymous delegates seem to capture state at point of
// definition, so they can't capture their own reference)
private string imageFilename;
private bool exit;

public void CaptureScreenshot(
  Uri address = null,
  string imageFilename = null,
  int msecDelay = 0,
  bool exit = false)
{
  handler = (s, e) =>
   {
     webBrowser.DocumentCompleted -= handler; //must do first

     this.imageFilename = imageFilename;
     this.exit = exit;

     timerScreenshot.Interval = (msecDelay>0)? msecDelay : 1;
     timerScreenshot.Enabled = true;
   };

  webBrowser.DocumentCompleted += handler;
  Go(address); //if address == null, will use URL from UI
}

private void timerScreenshot_Tick(object sender, EventArgs e)
{
  timerScreenshot.Enabled = false; //must do first

  BeginInvoke((Action)(() => //Invoke at UI thread
  { //run in UI thread

    BringToFront();
    Bitmap bitmap = webBrowser.GetScreenshot();

    if (imageFilename == null)
      imageFilename = bitmap.ShowSaveFileDialog();

    if (imageFilename != null)
    {
      Directory.CreateDirectory(
        Path.GetDirectoryName(
          Path.GetFullPath(imageFilename)));
               //create any parent directories needed
      bitmap.Save(imageFilename);
    }

    bitmap.Dispose(); //release bitmap resources

    if (exit)
      Close(); //this should close the app, this is main form

  }), null);
}

You can see the above in action at ClipFlair‘s WebCapture tool (http://gallery.clipflair.net/WebCapture, source code at: http://ClipFlair.codeplex.com, see Tools/WebCapture folder) that grabs screenshots from websites.

BTW, if you want to call the executable from command-line make sure you go to Properties of the project and at Security tab turn-off ClickOnce security (else it can’t access command-line).