Merged PR 21199: add info about TextBox.Text

add info about TextBox.Text

Author: jwmsft

windows.ui.xaml.data/binding_updatesourcetrigger.md

@@ -10,28 +10,44 @@ public Windows.UI.Xaml.Data.UpdateSourceTrigger UpdateSourceTrigger { get;  set;
 # Windows.UI.Xaml.Data.Binding.UpdateSourceTrigger
 
 ## -description
-Gets or sets a value that determines the timing of binding source updates for two-way bindings.
-
 
+Gets or sets a value that determines the timing of binding source updates for two-way bindings.
 
 ## -xaml-syntax
+
 ```xaml
 <Binding UpdateSourceTrigger="updateSourceTriggerMemberName"/>
 ```
-
-
 ## -xaml-values
+
 <dl><dt>updateSourceTriggerMemberName</dt><dd>updateSourceTriggerMemberNameA named constant from the UpdateSourceTrigger enumeration, such as Explicit.</dd>
 </dl>
+
 ## -property-value
-One of the [UpdateSourceTrigger](updatesourcetrigger.md) values. The default is **Default**, which evaluates as a **PropertyChanged** update behavior.
+
+One of the [UpdateSourceTrigger](updatesourcetrigger.md) values. The default is `Default`, which evaluates as a `PropertyChanged` update behavior for most dependency properties, but evaluates as `LostFocus` for the `TextBox.Text` property.
 
 ## -remarks
-Your other choice for an [UpdateSourceTrigger](updatesourcetrigger.md) behavior is to set the value to be **Explicit**. When a two-way binding has its [UpdateSourceTrigger](updatesourcetrigger.md) value as **Explicit**, you must explicitly call [UpdateSource](bindingexpression_updatesource_190615267.md) on the relevant [BindingExpression](bindingexpression.md) to cause the changed target values to update the data source. Use [GetBindingExpression](../windows.ui.xaml/frameworkelement_getbindingexpression_1210399878.md) to get a [BindingExpression](bindingexpression.md) from an object where a [Binding](binding.md) to a dependency property exists and that binding is a two-way binding with `UpdateSourceTrigger="Explicit"`.
+
+The default behavior for most dependency properties is `PropertyChanged`. However, the default behavior for the [TextBox.Text](../windows.ui.xaml.controls/textbox_text.md) property is `LostFocus`. For a [Binding](binding.md) to `TextBox.Text`, you can change the `UpdateSourceTrigger` like this:
+
+```xaml
+<TextBox Text="{x:Bind MyProperty, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
+```
+
+However, it won’t have any effect on a `TextBox` in the control template of another control, such as [NumberBox](/windows/winui/api/microsoft.ui.xaml.controls.numberbox). For example, this `UpdateSourceTrigger` setting has no effect.
+
+```xaml
+<!-- This UpdateSourceTrigger setting has no effect. -->
+<muxc:NumberBox Text="{x:Bind MyProperty, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
+```
+
+Your other choice for an [UpdateSourceTrigger](updatesourcetrigger.md) behavior is to set the value to be `Explicit`. When a two-way binding has its [UpdateSourceTrigger](updatesourcetrigger.md) value as `Explicit`, you must explicitly call [UpdateSource](bindingexpression_updatesource_190615267.md) on the relevant [BindingExpression](bindingexpression.md) to cause the changed target values to update the data source. Use [GetBindingExpression](../windows.ui.xaml/frameworkelement_getbindingexpression_1210399878.md) to get a [BindingExpression](bindingexpression.md) from an object where a [Binding](binding.md) to a dependency property exists and that binding is a two-way binding with `UpdateSourceTrigger="Explicit"`.
 
 You can't set the property values of a [Binding](binding.md) object after that binding has been attached to a target element and target property. If you attempt this you'll get a run-time exception.
 
 ## -examples
 
 ## -see-also
+
 [UpdateSource](bindingexpression_updatesource_190615267.md), [Mode](binding_mode.md), [XAML data binding sample](https://github.com/Microsoft/Windows-universal-samples/tree/master/Samples/XamlBind), [Data binding in depth](/windows/uwp/data-binding/data-binding-in-depth), [Dependency properties overview](/windows/uwp/xaml-platform/dependency-properties-overview), [GetBindingExpression](../windows.ui.xaml/frameworkelement_getbindingexpression_1210399878.md), [BindingOperations.SetBinding](bindingoperations_setbinding_746099660.md)

windows.ui.xaml.data/updatesourcetrigger.md

@@ -10,27 +10,31 @@ public enum Windows.UI.Xaml.Data.UpdateSourceTrigger : int
 # UpdateSourceTrigger
 
 ## -description
-Defines constants that indicate when a binding source is updated by its binding target in two-way binding.
-
 
+Defines constants that indicate when a binding source is updated by its binding target in two-way binding.
 
 ## -enum-fields
+
 ### -field Default:0
-Use default behavior from the dependency property that uses the binding. In Windows Runtime, this evaluates the same as a value with **PropertyChanged**.
+
+Use default behavior from the dependency property that uses the binding.
 
 ### -field PropertyChanged:1
+
 The binding source is updated whenever the binding target value changes. This is detected automatically by the binding system.
 
 ### -field Explicit:2
-The binding source is updated only when you call the [BindingExpression.UpdateSource](bindingexpression_updatesource_190615267.md) method.
 
+The binding source is updated only when you call the [BindingExpression.UpdateSource](bindingexpression_updatesource_190615267.md) method. (Not supported for `x:Bind`.)
 
 ### -field LostFocus:3
+
 The binding source is updated whenever the binding target element loses focus.
 
 ## -remarks
+
 > [!NOTE]
-> The default UpdateSourceTrigger value is **Default** rather than **PropertyChanged** for legacy reasons. Previous XAML frameworks enabled a way to register a dependency property with a value that influenced what its default binding update behavior does. That dependency property behavior isn't implemented in the Windows Runtime.
+> The default UpdateSourceTrigger value is `Default` rather than `PropertyChanged` for legacy reasons. This evaluates as a `PropertyChanged` update behavior for most dependency properties, but evaluates as `LostFocus` for the `TextBox.Text` property.
 
 ### Version history