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

I have seen similar issues with progress bars on Vista and Windows 7.

The key problem in my case was the blocking of the UI thread. (Like you do in your sample).

Windows does not like applications that don't respond to new messages in the message queue. If you spend too much time on one message, windows will mark your application as "not responsive". In Vista/Win7, windows also decides to stop updating your application window.

As a workaround, you could put the actual work on a background worker, or call Application.DoEvents() every once in a while. You do need to make sure that your progress bar window is modal, or else the DoEvents() may enable new commands to start executing halfway through your background processing.

If that feels to kludgy, the more proper way is to do your background work on a BackgroundWorker thread. It comes with support for sending events to the UI thread to update the progress bar.

Answer 2

I think the original problem is related to timing and Win7's (or Aero's) animation mechanism for the progress bar.

This Sub is on the form that contains the progress bar (pBar).

It varies the bar's .Maximum and keeps .Value fixed at 10 for percent completes of 1 to 99. The bar's .Minimum is set to 0 at design time.

This sorted out the problem for me.

Public Sub UpdateStatusPC(ByVal pc As Integer)

    Try

        If pc < 0 Then
            pBar.Maximum = 100
            pBar.Value = 0
        ElseIf pc > 100 Then
            pBar.Maximum = 100
            pBar.Value = 100
        ElseIf pc = 0 Then
            pBar.Maximum = 10
            pBar.Value = 0
        Else
            pBar.Value = 10
            pBar.Maximum = 10 / CDbl(pc / 100.0)
        End If

        pBar.Update()

    Catch ex As Exception

        MsgBox("UpdateStatusPC: " & ex.Message)

    End Try

End Sub

Answer 3

It has to do with the animation of the progress bar. If your progress bar is at 0% and you set it to 100% then it will not jump there, but animate the progress bar smoothly filling up. If this is too slow, you will be done before the progress bar finished animating. So even though you have already set it to 80, 90 and 100%, the animation still lags behind.

I never found a way to turn this off, however I have a workaround. The animation is only being done if you increment the progress bar. If you move it backwards, it will immediately jump to that position. So if I want the progress bar to be at x% (x != 100) then I move it to x+1 and then to x. If I want it at 100% I move it to 100, 99 and 100%. (Or whatever values you use, you get the idea.) This works fast enough to not to be visible, and you can leave this code in for previous Windows versions as well. (though I don't)

HTH

Answer 4

Disable visual effect option "Animate controls and elements inside windows" in "Performance options". Then the progressbars won't be animated any longer.