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dotnet-desktop-guide/framework/wpf/data/how-to-implement-binding-validation.md

@@ -0,0 +1,44 @@
+---
+title: "How to: Implement Binding Validation"
+description: Learn how to using binding validation to provide visual feedback to the user when an invalid value is entered in Windows Presentation Foundation (WPF). 
+ms.date: 03/30/2017
+dev_langs:
+ - csharp
+ - vb
+helpviewer_keywords: 
+  - "validation of binding [WPF]"
+  - "data binding [WPF], validation of binding"
+  - "binding [WPF], validation of"
+ms.assetid: eb98b33d-9866-49ae-b981-bc5ff20d607a
+---
+# How to: Implement Binding Validation
+
+This example shows how to use an <xref:System.Windows.Controls.Validation.ErrorTemplate%2A> and a style trigger to provide visual feedback to inform the user when an invalid value is entered, based on a custom validation rule.
+
+## Example
+
+The text content of the <xref:System.Windows.Controls.TextBox> in the following example is bound to the `Age` property (of type int) of a binding source object named `ods`. The binding is set up to use a validation rule named `AgeRangeRule` so that if the user enters non-numeric characters or a value that is smaller than 21 or greater than 130, a red exclamation mark appears next to the text box and a tool tip with the error message appears when the user moves the mouse over the text box.
+
+[!code-xaml[BindValidation#2](~/samples/snippets/csharp/VS_Snippets_Wpf/BindValidation/CSharp/Window1.xaml#2)]
+
+The following example shows the implementation of `AgeRangeRule`, which inherits from <xref:System.Windows.Controls.ValidationRule> and overrides the <xref:System.Windows.Controls.ValidationRule.Validate%2A> method. The `Int32.Parse` method is called on the value to make sure that it does not contain any invalid characters. The <xref:System.Windows.Controls.ValidationRule.Validate%2A> method returns a <xref:System.Windows.Controls.ValidationResult> that indicates if the value is valid based on whether an exception is caught during the parsing and whether the age value is outside of the lower and upper bounds.
+
+[!code-csharp[BindValidation#3](~/samples/snippets/csharp/VS_Snippets_Wpf/BindValidation/CSharp/AgeRangeRule.cs#3)]
+[!code-vb[BindValidation#3](~/samples/snippets/visualbasic/VS_Snippets_Wpf/BindValidation/VisualBasic/AgeRangeRule.vb#3)]
+
+The following example shows the custom <xref:System.Windows.Controls.ControlTemplate> `validationTemplate` that creates a red exclamation mark to notify the user of a validation error. Control templates are used to redefine the appearance of a control.
+
+[!code-xaml[BindValidation#4](~/samples/snippets/csharp/VS_Snippets_Wpf/BindValidation/CSharp/Window1.xaml#4)]
+
+As shown in the following example, the <xref:System.Windows.Controls.ToolTip> that shows the error message is created using the style named `textBoxInError`. If the value of <xref:System.Windows.Controls.Validation.HasError%2A> is `true`, the trigger sets the tool tip of the current <xref:System.Windows.Controls.TextBox> to its first validation error. The <xref:System.Windows.Data.Binding.RelativeSource%2A> is set to <xref:System.Windows.Data.RelativeSourceMode.Self>, referring to the current element.
+
+[!code-xaml[BindValidation#5](~/samples/snippets/csharp/VS_Snippets_Wpf/BindValidation/CSharp/Window1.xaml#5)]
+
+For the complete example, see [Bind Validation sample](https://github.com/Microsoft/WPF-Samples/tree/master/Data%20Binding/BindValidation).
+  
+Note that if you do not provide a custom <xref:System.Windows.Controls.Validation.ErrorTemplate%2A> the default error template appears to provide visual feedback to the user when there is a validation error. See "Data Validation" in [Data Binding Overview](/dotnet/desktop-wpf/data/data-binding-overview) for more information. Also, [!INCLUDE[TLA2#tla_winclient](../../../includes/tla2sharptla-winclient-md.md)] provides a built-in validation rule that catches exceptions that are thrown during the update of the binding source property. For more information, see <xref:System.Windows.Controls.ExceptionValidationRule>.
+
+## See also
+
+- [Data Binding Overview](/dotnet/desktop-wpf/data/data-binding-overview)
+- [How-to Topics](data-binding-how-to-topics.md)