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42 lines
2.9 KiB
Markdown
42 lines
2.9 KiB
Markdown
---
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title: "How to: Specify the Direction of the Binding"
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ms.date: "03/30/2017"
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helpviewer_keywords:
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- "direction of binding [WPF]"
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- "binding direction [WPF]"
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- "data binding [WPF], direction of binding"
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ms.assetid: 37334478-028b-4514-86c9-1420709f4818
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---
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# How to: Specify the direction of the binding
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This example shows how to specify whether the binding updates only the binding target (target) property, the binding source (source) property, or both the target property and the source property.
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## Example
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You use the <xref:System.Windows.Data.Binding.Mode%2A?displayProperty=nameWithType> property to specify the direction of the binding. The following are the available options for binding updates:
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- <xref:System.Windows.Data.BindingMode.TwoWay?displayProperty=nameWithType> updates the target property or the property whenever either the target property or the source property changes.
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- <xref:System.Windows.Data.BindingMode.OneWay?displayProperty=nameWithType> updates the target property only when the source property changes.
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- <xref:System.Windows.Data.BindingMode.OneTime?displayProperty=nameWithType> updates the target property only when the application starts or when the <xref:System.Windows.FrameworkElement.DataContext%2A> undergoes a change.
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- <xref:System.Windows.Data.BindingMode.OneWayToSource?displayProperty=nameWithType> updates the source property when the target property changes.
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- <xref:System.Windows.Data.BindingMode.Default?displayProperty=nameWithType> causes the default <xref:System.Windows.Data.Binding.Mode%2A> value of target property to be used.
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For more information, see the <xref:System.Windows.Data.BindingMode> enumeration.
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The following example shows how to set the <xref:System.Windows.Data.Binding.Mode%2A> property.
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[!code-xaml[DirectionalBinding#4](~/samples/snippets/csharp/VS_Snippets_Wpf/DirectionalBinding/CSharp/Page1.xaml#4)]
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To detect source changes (applicable to <xref:System.Windows.Data.BindingMode.OneWay> and <xref:System.Windows.Data.BindingMode.TwoWay> bindings), the source must implement a suitable property change notification mechanism such as <xref:System.ComponentModel.INotifyPropertyChanged>. See [Implement Property Change Notification](how-to-implement-property-change-notification.md) for an example of an <xref:System.ComponentModel.INotifyPropertyChanged> implementation.
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For <xref:System.Windows.Data.BindingMode.TwoWay> or <xref:System.Windows.Data.BindingMode.OneWayToSource> bindings, you can control the timing of the source updates by setting the <xref:System.Windows.Data.Binding.UpdateSourceTrigger%2A> property. See <xref:System.Windows.Data.Binding.UpdateSourceTrigger%2A> for more information.
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## See also
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- <xref:System.Windows.Data.Binding>
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- [Data Binding Overview](/dotnet/desktop-wpf/data/data-binding-overview)
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- [How-to Topics](data-binding-how-to-topics.md)
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