How to update ObservableCollection from inside a BackgroundWorker using MVVM?

Question

since two days I am trying to solve the following problem: I have a WPF control where a WrapPanel is bound to an ObservableCollection. An action changes the content of the O

Answer 1

The BackgroundWorker can help you in two ways.

To update the collection while the BGWorker is running, use the ProgressChanged event. The name of this event is misleading - while you can update the progress of a task, you can use actually use it for anything that needs to be done in the UI (calling) thread by passing an object using the UserState property of the ProgressChangedEventArgs.

The BGWorker also has an event when it finishes. Again, you can pass any information back to it that you'd like in the Result property of the RunWorkerCompletedEventArgs in the RunWorkerCompleted event.

The following code is from another thread that I answered about BackgroundWorker:

BackgroundWorker bgWorker = new BackgroundWorker();
ObservableCollection mNumbers = new ObservableCollection();

public Window1()
{
    InitializeComponent();
    bgWorker.DoWork += 
        new DoWorkEventHandler(bgWorker_DoWork);
    bgWorker.ProgressChanged += 
        new ProgressChangedEventHandler(bgWorker_ProgressChanged);
    bgWorker.RunWorkerCompleted += 
        new RunWorkerCompletedEventHandler(bgWorker_RunWorkerCompleted);
    bgWorker.WorkerReportsProgress = true;

    btnGenerateNumbers.Click += (s, e) => UpdateNumbers();

    this.DataContext = this;
}

void bgWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    progress.Visibility = Visibility.Collapsed;
    lstItems.Opacity = 1d;
    btnGenerateNumbers.IsEnabled = true;
}

void bgWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
    List numbers = (List)e.UserState;
    foreach (int number in numbers)
    {
         mNumbers.Add(number);
    }

    progress.Value = e.ProgressPercentage;
}

void bgWorker_DoWork(object sender, DoWorkEventArgs e)
{
    Random rnd = new Random();
    List numbers = new List(10);

    for (int i = 1; i <= 100; i++)
    {
        // Add a random number
        numbers.Add(rnd.Next());            

        // Sleep from 1/8 of a second to 1 second
        Thread.Sleep(rnd.Next(125, 1000));

        // Every 10 iterations, report progress
        if ((i % 10) == 0)
        {
            bgWorker.ReportProgress(i, numbers.ToList());
            numbers.Clear();
        }
    }
}

public ObservableCollection NumberItems
{
    get { return mNumbers; }
}

private void UpdateNumbers()
{
    btnGenerateNumbers.IsEnabled = false;
    mNumbers.Clear();
    progress.Value = 0;
    progress.Visibility = Visibility.Visible;
    lstItems.Opacity = 0.5;

    bgWorker.RunWorkerAsync();
}