title: WPF the textblock background color can't binding variable
body: <p>Excuse me.I am a noob.I want click the button to change the background's color of textblock. the value of variable can change ,but the background's color didn't change.There is my code.please help me.</p>
  
  <p>Visual studio 2017</p>
  
  <p><a href="https://i.stack.imgur.com/126wQ.png" rel="nofollow noreferrer">enter image description here</a></p>
  
  <p>WPF</p>
  
  <p>the TextBlock</p>
  
  <pre><code>&lt;TextBlock Width="75" Height="75" HorizontalAlignment="Center" Margin="205,187,626,468" FontSize="48"&gt;
          &lt;TextBlock.Style&gt;
              &lt;Style TargetType="TextBlock"&gt;
  
                  &lt;Setter Property="Text" Value="1" /&gt;
                  &lt;Setter Property="Background" Value="Red" /&gt;
                  &lt;Style.Triggers&gt;
                      &lt;DataTrigger Binding="{Binding Path=TestView,Mode=TwoWay}" Value="True"&gt;
                          &lt;Setter Property="Text" Value="1" /&gt;
                          &lt;Setter Property="Background" Value="Green" /&gt;
                      &lt;/DataTrigger&gt;
                  &lt;/Style.Triggers&gt;
              &lt;/Style&gt;
          &lt;/TextBlock.Style&gt;
      &lt;/TextBlock&gt;
  </code></pre>
  
  <p>and the Button</p>
  
  <p><code>&lt;Button Margin="202,596,564,0" VerticalAlignment="Top" Width="134" Click="buttonClick"&gt;
  &lt;/Button&gt;</code></p>
  
  <p>Xaml.cs</p>
  
  <pre><code>private bool testView = true;
      public bool TestView
      {
          get { return testView; }
          set { testView = value; }
      }
  
      private void buttonClick(object sender, RoutedEventArgs e)
      {
          TestView = false;
      }
  </code></pre>
  
  <p>I expect when testView == true,the background's color of textblock is Green when testView == false,the background's color of textblock is Red.
  and the Text is in the middle of TextBlock</p>