title: how to bind different tabItems to different ViewModels
body: <p>I don't want to put it all in one ViewModel, I want to have one viewModel per tabItem.</p>
  
  <p>I created a mainViewModel for the window containing the TabControl, where I have this property currentViewModel,pointed to a default value on the mainViewModel constructor </p>
  
  <pre><code>    public MainViewModel()
      {
          currentViewModel = "viewModel1";
      }
  </code></pre>
  
  <p>When a user clicks on another tabItem this executes</p>
  
  <pre><code>currentViewModel = "viewModel2";
  </code></pre>
  
  <p>and of course the set accessor has the onPropertyChanged method</p>
  
  <pre><code>    public String currentViewModel
      {
          get { return _currentViewModel; }
  
          set
          { 
              _currentViewModel = value;
              OnPropertyChanged("currentViewModel");
          }
      }
  </code></pre>
  
  <p>Another two viewModels (viewModel1,viewModel2) each one determines the functionality of one of the tabItems I want to switch between.</p>
  
  <p>Now on my Main.xaml I want to bind my dataContext to firstly the MainViewModel and then to the currentViewModel property. so that whenever user clicks on a tabItem the currentViewModel propert get updated and the dataContext point to the corresponding viewmodel.</p>