title: Updating databinding on LostFocus fail because of source changed before
body: <p>First, for information, we use MVVM light.</p>
  
  <p>I have a gridview containing object databinded and one property of the selected object could be modified through a global textbox (that is outside of the gridview).</p>
  
  <p>At the begining, the value of the property was updated through the textbox binding for each key pressed using the following code :</p>
  
  <pre><code>Text="{Binding Content, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
  </code></pre>
  
  <p>But we have heavy calculs made each time the value is modified that's why we choose too update the property only on LostFocus with the code :</p>
  
  <pre><code>Text="{Binding Content, Mode=TwoWay, UpdateSourceTrigger=LostFocus}"
  </code></pre>
  
  <p>And now I have a problem :(</p>
  
  <p>When the focus goes to another control of the application other than a line of the gridview, it works. The property is well updated with the value of the textbox. </p>
  
  <p>But if the focus goes to another line of the gridview, it doesn't work. In fact, when the new line is selected the content of our databinded property "Content" is updated with the value of the new selected line and it's AFTER that the databinding try to update the value when the event LostFocus occurs.</p>
  
  <p>So, the LostFocus occurs AFTER that the line has changed, that the property "Content" already contains the content of the new line and that's why the update of the property "Content" for the previously selected line do nothing.</p>
  
  <p>I try to do the databinding with the code : </p>
  
  <pre><code>Text="{Binding Content, Mode=TwoWay, UpdateSourceTrigger=Explicit}"
  </code></pre>
  
  <p>but failed to find an event fired before the "SelectionChange" where to update de property content. Do you know one?</p>
  
  <p>Or do you know have an idea how to bypass this problem? A clue? Or something that could help...
  Thanks!</p>