title: How to update ObservableCollection from inside a BackgroundWorker using MVVM?
body: <p>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 ObservableCollection. The content is loaded in a BackgroundWorker. Immediately after the action that caused the content change, the new content is needed in a foreach-loop. The problem is that the loading of the content is slow, so it needs a bit to get ready.</p>
  
  <p>My first attempt was to wait for the backgroundworker until the IsBusy property is set to false. But the IsBusy property never changed while waiting!
  Second attempt was to try to manipulate the ObservableCollection directly from the BackgroundWorker. Of course no success because the ObservableCollection is in another thread than the BackgroundWorker.</p>
  
  <p>I read really really much about how to manipulate content in cross-thread-wide. But none of them worked. Tried solutions with Dispatcher, "ThreadSafeObservableCollection", .....</p>
  
  <p>Might anyone tell me how I can solve that problem?
  Is there a simple way to edit content of the UI thread within another thread?
  Or how do I wait correctly for the BackgroundWorker to get finished?</p>
  
  <p><strong>EDIT:</strong>
  But how can I wait for the BackgroundWorker to get finished???</p>