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39 lines
2.4 KiB
Markdown
39 lines
2.4 KiB
Markdown
---
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title: "How to: Convert Bound Data"
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ms.date: "03/30/2017"
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dev_langs:
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- "csharp"
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- "vb"
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helpviewer_keywords:
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- "converting [WPF], bound data"
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- "data binding [WPF], converting bound data"
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- "binding data [WPF], converting bound data"
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ms.assetid: b00aaa19-c6df-4c3b-a9fd-88a0b488df2b
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---
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# How to: Convert Bound Data
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This example shows how to apply conversion to data that is used in bindings.
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To convert data during binding, you must create a class that implements the <xref:System.Windows.Data.IValueConverter> interface, which includes the <xref:System.Windows.Data.IValueConverter.Convert%2A> and <xref:System.Windows.Data.IValueConverter.ConvertBack%2A> methods.
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## Example
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The following example shows the implementation of a date converter that converts the date value passed in so that it only shows the year, the month, and the day. When implementing the <xref:System.Windows.Data.IValueConverter> interface, it is a good practice to decorate the implementation with a <xref:System.Windows.Data.ValueConversionAttribute> attribute to indicate to development tools the data types involved in the conversion, as in the following example:
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[!code-csharp[DataBindingLab#18](~/samples/snippets/csharp/VS_Snippets_Wpf/DataBindingLab/CSharp/DateConverter.cs#18)]
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[!code-vb[DataBindingLab#18](~/samples/snippets/visualbasic/VS_Snippets_Wpf/DataBindingLab/VisualBasic/DateConverter.vb#18)]
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Once you have created a converter, you can add it as a resource in your [!INCLUDE[TLA#tla_xaml](../../../includes/tlasharptla-xaml-md.md)] file. In the following example, *src* maps to the namespace in which *DateConverter* is defined.
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[!code-xaml[DataBindingLab#15](~/samples/snippets/csharp/VS_Snippets_Wpf/DataBindingLab/CSharp/DataBindingLabApp.xaml#15)]
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Finally, you can use the converter in your binding using the following syntax. In the following example, the text content of the <xref:System.Windows.Controls.TextBlock> is bound to *StartDate*, which is a property of an external data source.
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[!code-xaml[DataBindingLab#17](~/samples/snippets/csharp/VS_Snippets_Wpf/DataBindingLab/CSharp/DataBindingLabApp.xaml#17)]
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The style resources referenced in the above example are defined in a resource section not shown in this topic.
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## See also
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- [Implement Binding Validation](how-to-implement-binding-validation.md)
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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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