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Posted 2 Mar 2008

AJAX-style Asynchronous Progress Dialog for WinForms

, 2 Mar 2008
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A base class for adding a rich asynchronous progress animation to any Form.



My company develops a lot of rich-client applications, and we have forever wanted a nice "slick" way to indicate to the user when an activity is occurring in the background. Rarely do we know how long an operation will take (web services, remoting calls etc.), so we always use to just stick a little barber pole type animation in the top-right corner of the main application window. This was never a perfect solution though because we still had to do all the nasty "locking" of the Control/Form to make sure they couldn't queue up another action. Moreover, setting Enabled = False on many WinForms controls can look quite ugly and inconsistent, especially if the Form has got a variety of different controls.

In recent years, AJAX on the web has actually pioneered some interesting GUI concepts. I've always liked it when web sites pop-up with a central window that turns the background slightly darker and then ask you for some input. Then you type that input in and press an OK button, and then you get a nice little barber pole animation to indicate it has gone off back to the server and is waiting for a reply for the next step (if any).

That's basically what this project is about. Bringing that "cool" AJAX-style asynchronous indication behaviour to WinForms.


The project consists of several fundamental concepts:

  • Capturing/snap-shooting the current appearance of a Form in a reliable and consistent way. Note: Control.DrawToBitmap() was not used because it has weird behaviour with some controls like RichTextBox.
  • Manipulating the captured bitmap to either blur or grayscale it in some way, in a similar way that most AJAX web sites do.
  • A barber pole type animation in the center of the Form. In this case, I used the excellent "Loading Circle" control by Martin Gagne - so thank you Martin for that :~)
  • From the outset, I ensured that whatever I developed would work on both normal Forms and MDI child's. This was crucial to me because many of our products use MDI user interfaces. Secondly, this ruled out the possibility of using Win2000-onwards composited layered translucent windows (which I experimented with initially).

Using the code

To use the base class, simply modify your Form to derive from my AsyncBaseDialog instead of the default System.Windows.Forms.Form. You then just call RunAsyncOperation() and pass in your delegate method as its parameter. This method handles all the nitty-gritty work of scheduling your work on a background thread.

Alternatively, if you want better control over things, then you can use BeginAsyncIndication() and EndAsyncIndication().

Internally, Begin/EndAsyncIndication() use a reference count so that you can call them multiple times in a stack-like fashion and still get the expected behaviour.

public partial class MyForm : AsyncBaseDialog {

   public ModalDlg() {

   private void button1_Click(object sender, EventArgs e) {
      AsyncProcessDelegate d = delegate() {
         // Do your long-duration work here
         // and remove the placeholder Sleep() below


   private void button2_Click(object sender, EventArgs e) {
      // Alternatively if you don't want to use the RunAsyncOperation() wrapper...
      // You can use BeginAsyncIndication() and EndAsyncIndication() explicitly.


How it works

The Form is snapshot by opening up its DC (device context) and then copying its contents to a Bitmap. This bitmap is then manipulated using Martin Gagne's methods to grayscale it.

The snapshot of the Form was probably the hardest bit as I haven't done Win32 API for years! By the way, if you are have having teething issues with Control.DrawToBitmap(), then I recommend you look at this. Here it is:

// Get DC of the form...
IntPtr srcDc = GetDC(this.Handle);

// Create bitmap to store image of form...
Bitmap bmp = new Bitmap(this.ClientRectangle.Width, this.ClientRectangle.Height);

// Create a GDI+ context from the created bitmap...
using (Graphics g = Graphics.FromImage(bmp)) {
   // Copy image of form into bitmap...
   IntPtr bmpDc = g.GetHdc();
   BitBlt(bmpDc, 0, 0, bmp.Width, bmp.Height, srcDc, 0, 0, 0x00CC0020 /* SRCCOPY */);

   // Release resources...
   ReleaseDC(this.Handle, srcDc);

   // Blur/grayscale it...

   // Apply translucent overlay... fillBrush has an alpha-channel.
   g.FillRectangle(fillBrush, 0, 0, bmp.Width, bmp.Height);

There were a couple issues I had surrounding the user resizing, maximising, minimising, restoring, or double-clicking the title bar of the Form whilst the async. indication was active. Basically, these were redraw issues - particularly on pre-Vista Aero Glass machines. After weighing up possible solutions, I decided that the chances of a user wanting to resize/min/maximise the Form whilst the async. indication was active was pretty small and the annoyance to them would probably be very small. Therefore, I wrote some WndProc filters, as below:

protected override void WndProc(ref Message m) {
   if (IsAsyncBusy) {
      if (m.Msg == 0x112 /* WM_SYSCOMMAND */) {
         int w = m.WParam.ToInt32();

         if (w == 0xf120 /* SC_RESTORE */ || w == 0xf030 
                         /* SC_MAXIMIZE */ || w == 0xf020 
                         /* SC_MINIMIZE */)
            return; // short circuit

      } else if (m.Msg == 0xa3 /* WM_NCLBUTTONDBLCLK */)
         return; // short circuit

   base.WndProc(ref m);

Thank you

Thanks for reading and I hope you like the control.

If you make any modifications/bug fixes/enhancements to this control, please post in the comments section with your source snippets and/or ideas.


  • 02/March/2008 - initial release.


This article, along with any associated source code and files, is licensed under The Mozilla Public License 1.1 (MPL 1.1)


About the Author

Nathan Evans
Software Developer (Senior)
United Kingdom United Kingdom
I am the lead developer of numerous .NET-based networking and communication server systems for Windows, for a company based in Cambridge. Including SMS/SMPP, VOIP and VoiceXML technologies.

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Comments and Discussions

GeneralMy vote of 4 Pin
Ian Gallagher10-Jun-11 6:53
memberIan Gallagher10-Jun-11 6:53 

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