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Binding.ValidatesOnExceptions Property

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

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

public bool ValidatesOnExceptions { get; set; }

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 int age;

    public int Age
    {
        get { return age; }
        set
        {

            if (value < 0 || value > 150)
            {
                throw new ArgumentException("Age must not be less than 0 or greater than 150.");
            }
            age = value;
        }
    }
}

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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