Multithreading & thread.sleep freezes gui

Question

I am making a WinForms app in .net 4.0 (vb.net) and I would like to ask:

I am writing a piece of code that needs to run every specific interval. This task will firstly disable a button in the form and then do the work. At 2 points during this work, it must wait for 1sec and then proceed. When finished, it must re-enable the button.

During this whole procedure, I don't want to freeze the gui.

How should I implepent this? Must I use a background worker?

Feel free to answer me in c# or vb.net, whatever you like!

Thanks in advance!

EDIT: What I've done so far (I am using Aforge.NET framework to capture a camera screenshot):

I dragged a backgroung worker in the form. In its DoWork event, I entered the name of the main work:

Private Sub BackgroundWorker_camera_DoWork() Handles BackgroundWorker_camera.DoWork

        do_evaluation()

    End Sub

The do_evaluation sub must do some work, then wait for a second (for camera device to be ready), capture camera snapshot, wait for another second and finish work:

Public Delegate Sub do_evaluationDelegate()
    Public Sub do_evaluation()
        If Me.InvokeRequired Then
        Me.Invoke(New do_evaluationDelegate(AddressOf do_evaluation))
        Return
    End If


    ButtonX_Evaluate.Enabled = False
    ButtonX_restore.Enabled = False


    ...some work...

    evaluate_from_camera()

    ...some work...

     Main.ButtonX_Evaluate.Enabled = True
     Main.ButtonX_restore.Enabled = True

    ReleaseMemory()

End Sub

And the evaluate from camera sub:

 Public Delegate Sub evaluate_from_cameraDelegate()
    Public Sub evaluate_from_camera()
        If Me.InvokeRequired Then
            Me.Invoke(New evaluate_from_cameraDelegate(AddressOf evaluate_from_camera))
            Return
        End If

                    Aforge_cam.start_source()



                   'wait for 1sec
                    Thread.Sleep(1000)


                    AddHandler Aforge_cam.videoSource.NewFrame, AddressOf Aforge_cam.video_NewFrame

                    'wait for 1sec
                    Thread.Sleep(1000)

                    Aforge_cam.CloseVideoSource()


    End Sub

As the system requires a little time to connect to the hardware cam, the sub must wait for a second after the Aforge_cam.start_source() command, in order for the hardware to initialize fully.

Then, adding the handler for a new frame capture event in evaluate _from_camera will cause a new frame to be captured in a public variable "screenshot". As it requires some tenths of a second to capture a frame from the webcam, the code must wait for a capture of a bitmap in screenshot variable in order to continue. Hence the 2 sleep commands.

I begin the process with a RunWorkerAsync command to the background worker. Nevertheless, the GUI freezes and I cannot understand why, since background workers run on a separate thread, right?

Show us what you have tried so far. It's hard to answer as lack of information from you. A background worker would work and so would a new thread, but both are different depending on what you want... — Trevor, Oct 27 '14 at 12:42

score 0 · Accepted Answer · edited May 23 '17 at 10:32

0

You need to use a Timer in order to time your operations, using Thread.Sleep on the UI thread will freeze the GUI and is not meant for such tasks.

Just choose the one that fits you best.

edited May 23 '17 at 10:32

Community

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answered Oct 27 '14 at 12:51

Moti Azu

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Multithreading & thread.sleep freezes gui

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