title: WPF: MVVM - disable button if command is null
body: <p>I have binding on some command:</p>
  
  <pre><code>&lt;Button Command="{Binding Save}" /&gt;
  </code></pre>
  
  <p><strong>Save</strong> is command of some object that can be selected from list.
  In initial state there is no any selected object so binding does not work and <strong>CanExecute</strong> does not invoked. How can i disable this button using MVVM?</p>
  
  <p>Solution: <a href="https://stackoverflow.com/questions/4423746/wpf-mvvm-disable-a-buttons-state-when-the-viewmodel-behind-the-usercontrol-is-n/4424241#4424241">WPF/MVVM: Disable a Button&#39;s state when the ViewModel behind the UserControl is not yet Initialized?</a></p>
  
  <p>Guys, thanks for your answers and sorry for duplication of question.</p>