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    copied!<p>I had a look through the source code and the <code>BindingExpressionBase</code> itself is aware of this through a property called <code>NeedsUpdate</code>. But this property is internal so you would have to use reflection to get it.</p> <p>However, you won't be able to monitor this property in any easy way. So the way I see it, you would need to use both of the events <code>TextChanged</code> and <code>SourceUpdated</code> to know when <code>NeedsUpdate</code> might have changed.</p> <p><strong>Update</strong><br> I created an attached behavior that does this, it can be used to monitor pending updates on any <code>DependencyProperty</code>. <em>Note that <code>NotifyOnSourceUpdated</code> must be set to true</em>.</p> <p>Uploaded a small sample project here: <a href="http://dl.dropbox.com/u/39657172/PendingUpdateExample.zip">PendingUpdateExample.zip</a></p> <p><em>Example</em></p> <pre><code>&lt;TextBox Text="{Binding ElementName=textBoxSource, Path=Text, NotifyOnSourceUpdated=True, UpdateSourceTrigger=PropertyChanged, Delay=1000}" ab:UpdatePendingBehavior.MonitorPendingUpdates="{x:Static TextBox.TextProperty}"&gt; &lt;TextBox.Style&gt; &lt;Style TargetType="TextBox"&gt; &lt;Style.Triggers&gt; &lt;Trigger Property="ab:UpdatePendingBehavior.HasPendingUpdates" Value="True"&gt; &lt;Setter Property="Background" Value="Green"/&gt; &lt;/Trigger&gt; &lt;/Style.Triggers&gt; &lt;/Style&gt; &lt;/TextBox.Style&gt; &lt;/TextBox&gt; </code></pre> <p><strong>UpdatePendingBehavior</strong></p> <pre><code>public class UpdatePendingBehavior { #region MonitorPendingUpdates public static DependencyProperty MonitorPendingUpdatesProperty = DependencyProperty.RegisterAttached("MonitorPendingUpdates", typeof(DependencyProperty), typeof(UpdatePendingBehavior), new UIPropertyMetadata(null, MonitorPendingUpdatesChanged)); public static DependencyProperty GetMonitorPendingUpdates(FrameworkElement obj) { return (DependencyProperty)obj.GetValue(MonitorPendingUpdatesProperty); } public static void SetMonitorPendingUpdates(FrameworkElement obj, DependencyProperty value) { obj.SetValue(MonitorPendingUpdatesProperty, value); } public static void MonitorPendingUpdatesChanged(DependencyObject target, DependencyPropertyChangedEventArgs e) { DependencyProperty property = e.NewValue as DependencyProperty; if (property != null) { FrameworkElement element = target as FrameworkElement; element.SourceUpdated += elementProperty_SourceUpdated; if (element.IsLoaded == true) { SubscribeToChanges(element, property); } element.Loaded += delegate { SubscribeToChanges(element, property); }; element.Unloaded += delegate { UnsubscribeToChanges(element, property); }; } } private static void SubscribeToChanges(FrameworkElement element, DependencyProperty property) { DependencyPropertyDescriptor propertyDescriptor = DependencyPropertyDescriptor.FromProperty(property, element.GetType()); propertyDescriptor.AddValueChanged(element, elementProperty_TargetUpdated); } private static void UnsubscribeToChanges(FrameworkElement element, DependencyProperty property) { DependencyPropertyDescriptor propertyDescriptor = DependencyPropertyDescriptor.FromProperty(property, element.GetType()); propertyDescriptor.RemoveValueChanged(element, elementProperty_TargetUpdated); } private static void elementProperty_TargetUpdated(object sender, EventArgs e) { FrameworkElement element = sender as FrameworkElement; UpdatePendingChanges(element); } private static void elementProperty_SourceUpdated(object sender, DataTransferEventArgs e) { FrameworkElement element = sender as FrameworkElement; if (e.Property == GetMonitorPendingUpdates(element)) { UpdatePendingChanges(element); } } private static void UpdatePendingChanges(FrameworkElement element) { BindingExpressionBase beb = BindingOperations.GetBindingExpressionBase(element, GetMonitorPendingUpdates(element)); BindingFlags bindingFlags = BindingFlags.Instance | BindingFlags.NonPublic; PropertyInfo needsUpdateProperty = beb.GetType().GetProperty("NeedsUpdate", bindingFlags); SetHasPendingUpdates(element, (bool)needsUpdateProperty.GetValue(beb)); } #endregion // MonitorPendingUpdates #region HasPendingUpdates public static DependencyProperty HasPendingUpdatesProperty = DependencyProperty.RegisterAttached("HasPendingUpdates", typeof(bool), typeof(UpdatePendingBehavior), new UIPropertyMetadata(false)); public static bool GetHasPendingUpdates(FrameworkElement obj) { return (bool)obj.GetValue(HasPendingUpdatesProperty); } public static void SetHasPendingUpdates(FrameworkElement obj, bool value) { obj.SetValue(HasPendingUpdatesProperty, value); } #endregion // HasPendingUpdates } </code></pre> <hr> <p>Another way could be to use a <code>MultiBinding</code> that binds both to the source and the target and compares their values in a converter. Then you could change the <code>Background</code> in the <code>Style</code>. <em>This assumes that you don't convert the value</em>. Example with two <code>TextBoxes</code></p> <pre><code>&lt;TextBox Text="{Binding ElementName=textBoxSource, Path=Text, UpdateSourceTrigger=PropertyChanged, Delay=2000}"&gt; &lt;TextBox.Style&gt; &lt;Style TargetType="TextBox"&gt; &lt;Style.Triggers&gt; &lt;DataTrigger Value="False"&gt; &lt;DataTrigger.Binding&gt; &lt;MultiBinding Converter="{StaticResource IsTextEqualConverter}"&gt; &lt;Binding RelativeSource="{RelativeSource Self}" Path="Text"/&gt; &lt;Binding ElementName="textBoxSource" Path="Text"/&gt; &lt;/MultiBinding&gt; &lt;/DataTrigger.Binding&gt; &lt;Setter Property="Background" Value="Green"/&gt; &lt;/DataTrigger&gt; &lt;/Style.Triggers&gt; &lt;/Style&gt; &lt;/TextBox.Style&gt; &lt;/TextBox&gt; &lt;TextBox Name="textBoxSource"/&gt; </code></pre> <p><em>IsTextEqualConverter</em></p> <pre><code>public class IsTextEqualConverter : IMultiValueConverter { public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture) { return values[0].ToString() == values[1].ToString(); } public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture) { throw new NotSupportedException(); } } </code></pre>
 

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