One Way to Source Binding not working
<p>Ok quick summary is, I am trying to do a onewaytosource binding.</p>

<p>So explanation of my understanding of the  code. OneWaytoSource is the reverse of One Way binding. The target updates the source. So here my target is where I create the binding (so my textbox) my target property is the Foreground. My source is my menuItem and my source property is "IsEnabled". </p>

<p>The value converter is programmed in ConvertBack as this is the section that is meant for Onewaytosource or two way binding.</p>

<p>One of the textboxes:(I am planning to have this similar code on about 40 textboxes, which will disable my menuItem if the foreground is red)</p>

<pre><code> &lt;TextBox x:Name="upperLimitMinimum" Foreground="{Binding ElementName=menuItem, Path=IsEnabled, Mode=OneWayToSource, Converter={StaticResource myColorErrorConverter}}"
</code></pre>

<p>This is my code for converter:</p>

<pre><code>public class myColorErrorConverter : IValueConverter
 {
     public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
     {

        return null;
     }

     public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
     {
        if (null != value)
        {
            string x = value.ToString();
            if (x == "Red")
            { return true; }

        }
        return false;
    }
 }
</code></pre>

<p>My menuItem,</p>

<pre><code> &lt;MenuItem x:Name="menuItem"   Header="Menu Item( Ctrl + E )" Command="{Binding MenuItem}" 
</code></pre>

<p>What I expect to happen? When the textbox foreground turns red (which is controlled by a validation check, using a multivalue converter - not shown) The menuItem should become disabled. I have put a breakpoint on my converter and the code doesn't even enter the converter, so not really sure what is happening? Can someone shed some light on this?</p>

<p>After Clemens response, new code:</p>

<pre><code>    &lt;Style&gt;
 &lt;Style.Triggers&gt;
   &lt;DataTrigger Value="True"&gt;
     &lt;DataTrigger.Binding&gt;
       &lt;MultiBinding  Converter="{StaticResource MultiValueConverterColour}" &gt;
     &lt;Binding ElementName="upperLimitDefault" Path="Text" /&gt;
     &lt;Binding ElementName="upperLimitMaximum"  Path="Text" /&gt;
     &lt;Binding ElementName="upperLimitMinimum"  Path="Text" /&gt;
  &lt;/MultiBinding&gt;
&lt;/DataTrigger.Binding&gt;
 &lt;Setter Property="TextBox.Foreground" Value="Red"/&gt;
&lt;/DataTrigger&gt;
 &lt;/Style.Triggers&gt;

          &lt;Setter Property="TextBox.Foreground" Value="{Binding ElementName=MenuItem, Path=IsEnabled, Mode=OneWayToSource, Converter={StaticResource myColorErrorConverter}}" /&gt;
      &lt;/Style&gt;
</code></pre>

<p>So now at start up the 2nd converter is accessed and disables/enable menuitem accordingly, but during application running, when textbox foreground changes, only the first converter is accessed and the colour will change but second converter isn't accessed</p>