Application.DoEvents() in windows application.

Windows maintains a queue to hold various events like click, resize, close, etc. While a control is responding to an event, all other events are held back in the queue. So if your application is taking unduly long to process a button-click, rest of the application would appear to freeze. Consequently it is possible that your application appears unresponsive while it is doing some heavy processing in response to an event. While you should ideally do heavy processing in an asynchronous manner to ensure that the UI doesn’t freeze, a quick and easy solution is to just call Application.DoEvents() periodically to allow pending events to be sent to your application.

For good windows application, end user doesn’t like when any form of application are freezing out while performing larger/heavyweight operation. User always wants application run smoothly and in responsive manner rather than freezing UI. But after googling i found that Application.DoEvents() is not a good practice to use in application more frequently so instead this events it’s better to use BackGround Worker Thread for performing long running task without freezing windows.

You can get better idea if you practically look it. Just copy following code and check application with and without putting Application.DoEvents().

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        For i As Integer = 0 To 1000

            System.Threading.Thread.Sleep(100)

            ListBox1.Items.Add(i.ToString())

            Application.DoEvents()

        Next

    End Sub