• Article

ValidationAttribute Class

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Serves as the base class for all validation attributes.

Namespace:  System.ComponentModel.DataAnnotations
Assembly:  System.ComponentModel.DataAnnotations (in System.ComponentModel.DataAnnotations.dll)

Syntax

'Declaration
Public MustInherit Class ValidationAttribute _
    Inherits Attribute

public abstract class ValidationAttribute : Attribute

The ValidationAttribute type exposes the following members.

Constructors

  Name Description
Protected method ValidationAttribute() Initializes a new instance of the ValidationAttribute class.
Protected method ValidationAttribute(Func<String>) Initializes a new instance of the ValidationAttribute class with the specified function to retrieve the error message.
Protected method ValidationAttribute(String) Initializes a new instance of the ValidationAttribute class with the specified error message.

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Properties

  Name Description
Public property ErrorMessage Gets or sets the non-localizable error message to display when validation fails.
Public property ErrorMessageResourceName Gets or sets the property name on the resource type that provides the localizable error message.
Public property ErrorMessageResourceType Gets or sets the resource type that provides the localizable error message.
Protected property ErrorMessageString Gets the localized or non-localized error message.

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Methods

  Name Description
Public method Equals Infrastructure. Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute.)
Protected method Finalize Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
Public method FormatErrorMessage Applies formatting to the error message.
Public method GetHashCode Returns the hash code for this instance. (Inherited from Attribute.)
Public method GetType Gets the Type of the current instance. (Inherited from Object.)
Public method GetValidationResult Determines whether the specified object is valid and returns an object that includes the results of the validation check.
Protected method IsValid Determines whether the specified object is valid.
Public method Match When overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute.)
Protected method MemberwiseClone Creates a shallow copy of the current Object. (Inherited from Object.)
Public method ToString Returns a string that represents the current object. (Inherited from Object.)
Public method Validate Determines whether the specified object is valid and throws a ValidationException if the object is not valid.

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Remarks

You create a class that derives from the ValidationAttribute class when you need to create a customized validation attribute. You override the IsValid method to provide the logic for your customized validation check.

The Validate method calls the IsValid method and raises a ValidationException if the value is not valid. The GetValidationResult method calls the IsValid method and returns an instance of the ValidationResult class to indicate the result of the validation check.

Examples

The following example shows a customized validation attribute that derives from ValidationAttribute. The class overrides the IsValid method to test whether the value is valid. By default, the attribute displays an error message that is included as a resource in the application.

Public Class EvenNumberAttribute
    Inherits ValidationAttribute

    Public Sub New()
        MyBase.New(Function() My.Resources.Resource1.EvenNumberError)
    End Sub

    Public Sub New(ByVal errorMessage As String)
        MyBase.New(Function() errorMessage)
    End Sub


    Protected Overrides Function IsValid(ByVal value As Object, _
                ByVal validationContext As ValidationContext) As ValidationResult
        If (value = Nothing) Then
            Return ValidationResult.Success
        End If

        Dim convertedValue As Integer
        Try
            convertedValue = Convert.ToInt32(value)
        Catch ex As FormatException
            Return New ValidationResult(My.Resources.Resource1.ConversionError)
        End Try

        If (convertedValue Mod 2 = 0) Then
            Return ValidationResult.Success
        Else
            Return New ValidationResult(FormatErrorMessage(validationContext.DisplayName))
        End If
    End Function
End Class

public class EvenNumberAttribute : ValidationAttribute
{
    public EvenNumberAttribute() : base(() => Resource1.EvenNumberError) { }
    public EvenNumberAttribute(string errorMessage) : base(() => errorMessage) { }

    protected override ValidationResult IsValid(object value, 
        ValidationContext validationContext)
    {
        if (value == null)
        {
            return ValidationResult.Success;
        }

        int convertedValue;
        try
        {
            convertedValue = Convert.ToInt32(value);
        }
        catch (FormatException)
        {
            return new ValidationResult(Resource1.ConversionError);
        }

        if (convertedValue % 2 == 0)
        {
            return ValidationResult.Success;
        }
        else
        {
            return new ValidationResult(FormatErrorMessage(validationContext.DisplayName));
        }
    }
}

Version Information

Silverlight

Supported in: 5, 4, 3

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.