Question

I have a simple ‘Working’ form that runs on its own thread to keep the user informed that the application hasn’t died during long running operations. In order to get the working form to update I had to insert a DoEvents() call.

I’m curious, will this only pump messages for the current thread I’m in, or will it do it for the whole application? I would prefer that the main window stay unresponsive till the operation finishes, so I’m curious as to the behavior. Below is the code for the working form.

Just to be clear, I’m fine with the code I have, but I would like to know how DoEvents() behaves with threads.

    Public Class frmWorking

    ''' <summary>
    ''' Creates and starts a new thread to handle the Working Dialog
    ''' </summary>
    ''' <returns>The thread of the Working dialog.</returns>
    ''' <remarks></remarks>
    Public Shared Function StartWait() As WorkingFromToken
        Dim th As New Threading.Thread(AddressOf ShowWait)
        Dim token As New WorkingFromToken
        th.Start(token)
        Return token
    End Function

    Private Shared Sub ShowWait(token As WorkingFromToken)
        Dim frm As New frmWorking
        Try
            frm.Show()
            Do
                If frm.txtWait.Text.Length > 45 Then
                    frm.txtWait.Text = "Working"
                Else
                    frm.txtWait.Text &= "."
                End If
                Windows.Forms.Application.DoEvents()
                Threading.Thread.Sleep(250)
            Loop While token.Running
            frm.Hide()

        Catch ex As Threading.ThreadAbortException
            Threading.Thread.ResetAbort()
            frm.Hide()
            Return
        End Try

    End Sub

End Class

Answer 1

DoEvents will only pump the current UI thread.

However, I do not recommend your approach.

Instead, you should do your work on a background thread, and show a modal progress form on the UI thread and update it using BeginInvoke or a BackgroundWorker.