Binding.ValidatesOnExceptions Property

 

Gets or sets a value that indicates whether to include the ExceptionValidationRule.

Namespace:   System.Windows.Data
Assembly:  PresentationFramework (in PresentationFramework.dll)

Public Property ValidatesOnExceptions As Boolean

Property Value

Type: System.Boolean

true to include the ExceptionValidationRule; otherwise, false.

Setting this property provides an alternative to using the ExceptionValidationRule element explicitly. The ExceptionValidationRule is a built-in validation rule that checks for exceptions that are thrown during the update of the source property. If an exception is thrown, the binding engine creates a ValidationError with the exception and adds it to the Validation.Errors collection of the bound element. The lack of an error clears this validation feedback, unless another rule raises a validation issue.

ValidatesOnExceptions is introduced in the .NET Framework version 3.5. For more information, see .NET Framework Versions and Dependencies.

The following examples use ValidatesOnExceptions to validate user input in a TextBox. The first example creates a data type that throws an exception when the Age property is set to an invalid property.

Public Class PersonThrowException
    Private m_age As Integer

    Public Property Age() As Integer
        Get
            Return m_age
        End Get
        Set(ByVal value As Integer)

            If value < 0 OrElse value > 150 Then
                Throw New ArgumentException("Age must not be less than 0 or greater than 150.")
            End If
            m_age = value
        End Set
    End Property
End Class

The following example binds the Age property to the TextBox and sets ValidatesOnExceptions to true on the Binding. When the user enters an invalid value, a red border appears in the TextBox and the ToolTip reports the error message.

<StackPanel Margin="20">
  <StackPanel.Resources>

    <src:PersonThrowException x:Key="data"/>

    <!--The tool tip for the TextBox to display the validation error message.-->
    <Style x:Key="textBoxInError" TargetType="TextBox">
      <Style.Triggers>
        <Trigger Property="Validation.HasError" Value="true">
          <Setter Property="ToolTip"
              Value="{Binding RelativeSource={x:Static RelativeSource.Self},
              Path=(Validation.Errors)[0].ErrorContent}"/>
        </Trigger>
      </Style.Triggers>
    </Style>

  </StackPanel.Resources>
  <TextBlock>Enter your age:</TextBlock>
  <TextBox Style="{StaticResource textBoxInError}">
    <TextBox.Text>
      <!--By setting ValidatesOnExceptions to True, it checks for exceptions
        that are thrown during the update of the source property.
        An alternative syntax is to add <ExceptionValidationRule/> within
        the <Binding.ValidationRules> section.-->
      <Binding Path="Age" Source="{StaticResource data}"
               ValidatesOnExceptions="True"
               UpdateSourceTrigger="PropertyChanged">
      </Binding>
    </TextBox.Text>
  </TextBox>
  <TextBlock>Mouse-over to see the validation error message.</TextBlock>
</StackPanel>

.NET Framework
Available since 3.0
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
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