Question

I have a button that on click event I get some information from the network.

When I get information I parse it and add items to ListBox. All is fine, but when I do a fast double-click on button, it seems that two background workers are running and after finishing all work, items in the list are dublicated.

I want to do so that if you click button and the proccess of getting information is in work, this thread is stopping and only after first work is completed the second one is beginning.
Yes, I know about AutoResetEvent, but when I used it it helped me only one time and never more. I can’t implement this situation and hope that you will help me!

Now I even try to make easier but no success 🙁 : I added a flag field(RefreshDialogs)(default false), when the user clicks on button, if flag is true(it means that work is doing), nothing is doing, but when flag field is set to false, all is fine and we start a new proccess.
When Backgroundwork completes, I change field flag to false(it means that user can run a new proccess).

    private void Message_Refresh_Click(object sender, EventArgs e)
    {
        if (!RefreshDialogs)
        {
            RefreshDialogs = true;
            if (threadBackgroundDialogs.WorkerSupportsCancellation)
            {
                threadBackgroundDialogs.CancelAsync();
            }
            if (!threadBackgroundDialogs.IsBusy)
            {
                downloadedDialogs = 0;
                threadBackgroundDialogs = new BackgroundWorker();
                threadBackgroundDialogs.WorkerSupportsCancellation = true;
                threadBackgroundDialogs.DoWork += LoadDialogs;
                threadBackgroundDialogs.RunWorkerCompleted += ProcessCompleted;
                threadBackgroundDialogs.RunWorkerAsync();
            }
        }
    }
    void ProcessCompleted(object sender,  RunWorkerCompletedEventArgs e)
    {
        RefreshDialogs = false;
    }

Answer 1

I’m not an Windows Phone expert, but as I see it has support for TPL, so following code would read nicely:

private object syncRoot =new object();
private Task latestTask;

public void EnqueueAction(System.Action action)
{
    lock (syncRoot)
    {
        if (latestTask == null)
            latestTask = Task.Factory.StartNew(action);
        else
            latestTask = latestTask.ContinueWith(tsk => action());
    }
}