title: How can I update UI when Observable.Context is not available?
body: <p>I have a WinFrom App, use synchronous method to download string from a url, and use Rx ToAsync Method to make it asynchronous and get the observable result, and when the result comes I show it on the Form.</p>
  
  <p>Yesterday, I updated Rx to the latest release, and it was told that "Observable does not contain a definition of Context". I tried comment this line, the codes threw an exception that "Cross-thread operation not valid: Control 'tbx_Reference' accessed from a thread other than the thread it was created on." </p>
  
  <p>I want to show the asynchronous result using Subscribe method. How can I fix this problem? thanks very much.</p>
  
  <pre><code>public static IObservable&lt;TResult&gt; DoWorkAsync(TParameter parameter,
          Func&lt;TParameter,TResult&gt; actionSync)
      {
          Observable.Context = SynchronizationContext.Current;
  
          Func&lt;TParameter, IObservable&lt;TResult&gt;&gt; ActionAsync =  actionSync.ToAsync();
  
          IObservable&lt;TResult&gt; results = from result in ActionAsync(parameter)
                                         select result;
  
          return results;
      }
  </code></pre>