title: Get index of item in bindable collection
body: <p>In this listbox i display contact names. </p>
  
  <pre><code>&lt;ListBox x:Name="Items" Margin="36,38,78,131"&gt;
      &lt;ListBox.ItemTemplate&gt;
          &lt;DataTemplate&gt;
                  &lt;StackPanel Orientation="Horizontal"&gt;
                      &lt;TextBlock x:Name="lol" Text="{Binding Path=ContactName}" Style="{StaticResource PhoneTextSmallStyle}"
  Width="Auto" TextAlignment="Center" FontWeight="Bold" Foreground="White" VerticalAlignment="Bottom" TextWrapping="Wrap"/&gt;
                      &lt;Button x:Name="ShowName"&gt;
                          &lt;i:Interaction.Triggers&gt;
                              &lt;i:EventTrigger EventName="Click"&gt;
                                  &lt;cal:ActionMessage MethodName="delete" /&gt;
                              &lt;/i:EventTrigger&gt;
                          &lt;/i:Interaction.Triggers&gt;
                      &lt;/Button&gt;
                  &lt;/StackPanel&gt;
          &lt;/DataTemplate&gt;
      &lt;/ListBox.ItemTemplate&gt;
  &lt;/ListBox&gt;
  </code></pre>
  
  <p>I get contacts from local DB</p>
  
  <pre><code>public List&lt;FBContacts&gt; listContactDatas { get; set; }
  
  Items = new BindableCollection&lt;FBContacts&gt;();= new BindableCollection&lt;FBContacts&gt;();
  
  public void GetContacts()
      {
         using(MyDataContext mydb = new MyDataContext(DBConnectionstring))
         { 
          var items = from ContactsList Name in mydb._contacts select Name;
          foreach (var toDoItem in items)
          {
             Items.Add(new FBContacts()
                  {
                      ContactName = toDoItem.Name
                  });
          }
          }
      }
  </code></pre>
  
  <p>user can delete any contact if he press button.</p>
  
  <pre><code>public void delete()
      {
          Items.RemoveAt(/* index*/);
      }
  </code></pre>
  
  <p>so how i can get index of choosen contact?</p>