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UpdateSourceTrigger Enumeration

Describes the timing of binding source updates.

Namespace:  System.Windows.Data
Assembly:  PresentationFramework (in PresentationFramework.dll)
public enum UpdateSourceTrigger
<object property="enumerationMemberName" .../>
Member nameDescription
DefaultThe default UpdateSourceTrigger value of the binding target property. The default value for most dependency properties is PropertyChanged, while the Text property has a default value of LostFocus.

A programmatic way to determine the default UpdateSourceTrigger value of a dependency property is to get the property metadata of the property using GetMetadata and then check the value of the DefaultUpdateSourceTrigger property.

PropertyChangedUpdates the binding source immediately whenever the binding target property changes.
LostFocusUpdates the binding source whenever the binding target element loses focus.
ExplicitUpdates the binding source only when you call the UpdateSource method.

For more information, see Binding.UpdateSourceTrigger.

This topic describes how to use the UpdateSourceTrigger property to control the timing of binding source updates. The topic uses the TextBox control as an example.

The TextBox.Text property has a default UpdateSourceTrigger value of LostFocus. This means if an application has a TextBox with a data-bound TextBox.Text property, the text you type into the TextBox does not update the source until the TextBox loses focus (for instance, when you click away from the TextBox).

If you want the source to get updated as you are typing, set the UpdateSourceTrigger of the binding to PropertyChanged. In the following example, the Text properties of both the TextBox and the TextBlock are bound to the same source property. The UpdateSourceTrigger property of the TextBox binding is set to PropertyChanged.

<Label>Enter a Name:</Label>
<TextBox>
  <TextBox.Text>
    <Binding Source="{StaticResource myDataSource}" Path="Name"
             UpdateSourceTrigger="PropertyChanged"/>
  </TextBox.Text>
</TextBox>

<Label>The name you entered:</Label>
<TextBlock Text="{Binding Source={StaticResource myDataSource}, Path=Name}"/>

As a result, the TextBlock shows the same text (because the source changes) as the user enters text into the TextBox, as illustrated by the following screenshot of the sample:

Simple data binding sample screen shot

For the complete sample, see Simple Binding Sample.

If you have a dialog or a user-editable form and you want to defer source updates until the user is finished editing the fields and clicks "OK", you can set the UpdateSourceTrigger value of your bindings to Explicit, as in the following example:

<TextBox Name="itemNameTextBox"
         Text="{Binding Path=ItemName, UpdateSourceTrigger=Explicit}" />

When you set the UpdateSourceTrigger value to Explicit, the source value only changes when the application calls the UpdateSource method. The following example shows how to call UpdateSource for itemNameTextBox:

// itemNameTextBox is an instance of a TextBox
BindingExpression be = itemNameTextBox.GetBindingExpression(TextBox.TextProperty);
be.UpdateSource();

For the complete sample, see Explicitly Updating the Binding Source Sample.

NoteNote:

You can use the same technique for properties of other controls, but keep in mind that most other properties have a default UpdateSourceTrigger value of PropertyChanged. For more information, see the UpdateSourceTrigger property page.

NoteNote:

The UpdateSourceTrigger property deals with source updates and therefore is only relevant for TwoWay or OneWay bindings. For TwoWay and OneWay bindings to work, the source object needs to provide property change notifications. You can refer to the samples cited in this topic for more information. In addition, you can look at How to: Implement Property Change Notification.

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0
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