title: MEF import and export not working
body: <p>I am trying to do a WPF application without using prism.When I tried to get my viewmodel in the view through mef by impoting constructor it not working.Also I have a property injection in my code that is also giving a null reference. 
  Is this because of not overriding composite container, if so how/where to give a composite container in an application without prism.
  My code is like this
  In xaml file design instance is set to viewmodel and cs file is like</p>
  
  <p>MainWindow.xaml.cs</p>
  
  <pre><code>public MainWindow()
      {
          InitializeComponent();            
      }
  
      [ImportingConstructor]
      public MainWindow(MainWindowViewModel viewModel) :this()
      {
          this.DataContext = viewModel;
          this.ViewModel = viewModel;
      }
      public MainWindowViewModel ViewModel { get; set; }
  
  [Export] 
  public class MainWindowViewModel 
  {    
  }
  </code></pre>
  
  <p>the breakpoint at the constructor of MainWindow.xaml.cs is not hitting at all.Inside viewmodel the property injection is also not hitting.
  How can I resolve this problem?</p>