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Binding.ValidatesOnDataErrors Property

Updated: February 2009

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

Namespace:  System.Windows.Data
Assembly:  PresentationFramework (in PresentationFramework.dll)
XMLNS for XAML: http://schemas.microsoft.com/winfx/2006/xaml/presentation, http://schemas.microsoft.com/netfx/2007/xaml/presentation

'Declaration
Public Property ValidatesOnDataErrors As Boolean
'Usage
Dim instance As Binding 
Dim value As Boolean 

value = instance.ValidatesOnDataErrors

instance.ValidatesOnDataErrors = value
<object ValidatesOnDataErrors="bool" .../>

Property Value

Type: System.Boolean
true to include the DataErrorValidationRule; otherwise, false.

Setting this property provides an alternative to using the DataErrorValidationRule element explicitly. The DataErrorValidationRule is a built-in validation rule that checks for errors that are raised by the IDataErrorInfo implementation of the source object. If an error is raised, the binding engine creates a ValidationError with the error 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.

ValidatesOnDataErrors is introduced in the .NET Framework version 3.5. For more information, see .NET Framework 3.5 Architecture.

The following examples uses IDataErrorInfo and ValidatesOnDataErrors to validate user input in a TextBox. The first example creates a data type that implements IDataErrorInfo to report validation errors.

Public Class PersonImplementsIDataErrorInfo
    Implements System.ComponentModel.IDataErrorInfo
    Private m_age As Integer 

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

    Public ReadOnly Property [Error]() As String _
                    Implements System.ComponentModel.IDataErrorInfo.Error
        Get 
            Return "" 
        End Get 
    End Property

    Default Public ReadOnly Property Item(ByVal name As String) As String _
                            Implements System.ComponentModel.IDataErrorInfo.Item
        Get 
            Dim result As String = Nothing 

            If name = "Age" Then 
                If Me.m_age < 0 OrElse Me.m_age > 150 Then
                    result = "Age must not be less than 0 or greater than 150." 
                End If 
            End If 
            Return result
        End Get 
    End Property 
End Class

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

<StackPanel Margin="20">
  <StackPanel.Resources>
    <src:PersonImplementsIDataErrorInfo 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>
      <!--ValidatesOnDataErrors to is set to True, so the Binding
          checks for errors raised by the IDataErrorInfo object.
          An alternative syntax is to add <DataErrorValidationRule/> within
          the <Binding.ValidationRules> section.-->
      <Binding Path="Age" Source="{StaticResource data}"
               ValidatesOnDataErrors="True"
               UpdateSourceTrigger="PropertyChanged">
      </Binding>
    </TextBox.Text>
  </TextBox>
  <TextBlock>Mouse-over to see the validation error message.</TextBlock>
</StackPanel>

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5 SP1, 3.0 SP1

Date

History

Reason

February 2009

Added example.

Customer feedback.

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