Windows 7 Aero Theme Progress Bar Bug?

Question

I have ran into what I consider to be a progress bar bug on Windows 7. To demonstrate the bug I created a WinForm application with a button and a progress bar. In the button's 'on-click' handle I have the following code.

private void buttonGo_Click(object sender, EventArgs e)
{
  this.progressBar.Minimum = 0;
  this.progressBar.Maximum = 100;

  this.buttonGo.Text = "Busy";
  this.buttonGo.Update();

  for (int i = 0; i <= 100; ++i)
  {
    this.progressBar.Value = i;
    this.Update();

    System.Threading.Thread.Sleep(10);
  }

  this.buttonGo.Text = "Ready";
}

The expected behavior is for the progress bar to advance to 100% and then the button text to change to 'Ready'. However, when developing this code on Windows 7, I noticed that the progress bar would rise to about 75% and then the button text would change to 'Ready'. Assuming the code is synchronous, this should not happen!

On further testing I found that the exact same code running on Windows Server 2003 produced the expected results. Furthermore, choosing a non aero theme on Windows 7 produces the expected results.

In my mind, this seems like a bug. Often it is very hard to make a progress bar accurate when the long operation involves complex code but in my particular case it was very straight forward and so I was little disappointed when I found the progress control did not accurately represent the progress.

Has anybody else noticed this behavior? Has anybody found a workaround?

Answer 1

To Delphi users facing the same problem: Below is a unit called ProgressBarFix that you can use to automatically patch the problem without worrying about changing your progress bar code -- just include ProgressBarFix in your form's interface "uses" clause after the ComCtrls uses and you'll get the workaround automatically:

unit ProgressBarFix;
(* The standard progress bar fails under Windows theming -- it fails to animate
   all the way to the right side. C.f.,
   http://stackoverflow.com/questions/2217688/windows-7-aero-theme-progress-bar-bug

   To work around the problem, include ProgressBarFix in the interface section's
   "uses" clause *after* ComCtrls (this replaces the TProgressBar definition in
   ConCtrls with the one here, effectively allowing the control defined on the
   form to be replaced with the patch version.

   c.f., http://www.deltics.co.nz/blog/?p=222and http://melander.dk/articles/splitter *)

interface
uses ComCtrls ;

type TProgressBar = class(ComCtrls.TProgressBar)
private
    procedure SetPosition(Value: Integer);
    function GetPosition: Integer;
published
    property Position: Integer read GetPosition write SetPosition default 0;
end ;

implementation

{ TProgressBar }

function TProgressBar.GetPosition: Integer;
begin
    result := inherited Position
end;

procedure TProgressBar.SetPosition(Value: Integer);
begin
    if Value=inherited Position then
        exit ;
    if value<Max then begin
        inherited Position := value+1 ;
        inherited Position := value
    end else begin
        Max := Max+1 ;
        inherited Position := Max ;
        inherited Position := value ;
        Max := Max-1
    end            
end;

end.