c#wpf garbage-collection backgroundworker

WPF, Background worker and garbage collection

Consider the following example

  public class ChildViewModel
  {
    public BackgroundWorker BackgroundWorker;

    public ChildViewModel()
    {
        InitializeBackgroundWorker();
        BackgroundWorker.RunWorkerAsync();
    }

    private void InitializeBackgroundWorker()
    {
        BackgroundWorker = new BackgroundWorker();
        BackgroundWorker.DoWork += backgroundWorker_DoWork;
        BackgroundWorker.RunWorkerCompleted +=backgroundWorker_RunWorkerCompleted;
    }

    private void backgroundWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        //do something
    }

    void backgroundWorker_DoWork(object sender, DoWorkEventArgs e)
    {
        //do time consuming task
        Thread.Sleep(5000);
    }

    public void UnregisterEventHandlers()
    {
        BackgroundWorker.DoWork -= backgroundWorker_DoWork;
        BackgroundWorker.RunWorkerCompleted -= backgroundWorker_RunWorkerCompleted;
    }

}

public class ParentViewModel
{
    ChildViewModel childViewModel;

    public ParentViewModel()
    {
        childViewModel = new ChildViewModel();
        Thread.Sleep(10000);
        childViewModel = null;
        //would the childViewModel now be eligible for garbage collection at this point or would I need to unregister the background worker event handlers by calling UnregisterEventHandlers?  
    }
}

Question: Do I need to unregister the background workers event handlers for the childViewModel object to be eligible for garbage collection. (This is just an example. I am aware I can use TPL in this situation without the need for a background worker but I am curious about this specific scenario. )

Solution

It depends a bit on why your backgroundworker is public. But if your ViewModel class is the only class holding a strong reference to the background worker, and the background worker is holding a hard reference to the viewmodel (via the two events), both will be marked for garbage collection once the view model is not hold by any reference anymore.