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How to: Set Up Notification of Binding Updates

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This example shows how to set up to be notified when the binding target (target) or the binding source (source) property of a binding has been updated.

Example

Windows Presentation Foundation (WPF) raises a data update event each time that the binding source or target has been updated. Internally, this event is used to inform the user interface (UI) that it should update, because the bound data has changed. Note that for these events to work, and also for one-way or two-way binding to work properly, you need to implement your data class using the INotifyPropertyChanged interface. For more information, see Implement Property Change Notification.

Set the NotifyOnTargetUpdated or NotifyOnSourceUpdated property (or both) to true in the binding. The handler you provide to listen for this event must be attached directly to the element where you want to be informed of changes, or to the overall data context if you want to be aware that anything in the context has changed.

Here is an example that shows how to set up for notification when a target property has been updated.

<TextBlock Grid.Row="1" Grid.Column="1" Name="RentText"
           Text="{Binding Path=Rent, Mode=OneWay, NotifyOnTargetUpdated=True}"
           TargetUpdated="OnTargetUpdated"/>

You can then assign a handler based on the EventHandler<T> delegate, OnTargetUpdated in this example, to handle the event:

private void OnTargetUpdated(object sender, DataTransferEventArgs args)
{
    // Handle event
}

Private Sub OnTargetUpdated(sender As Object, e As DataTransferEventArgs)
    ' Handle event
End Sub

Parameters of the event can be used to determine details about the property that changed (such as the type or the specific element if the same handler is attached to more than one element), which can be useful if there are multiple bound properties on a single element.

See also