RequiredAttribute Class

Specifies that a value must be provided for a property.

Inheritance Hierarchy

System.Object
  System.Attribute
    System.ComponentModel.DataAnnotations.ValidationAttribute
      System.ComponentModel.DataAnnotations.RequiredAttribute

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

Syntax

'Declaration
<AttributeUsageAttribute(AttributeTargets.Property Or AttributeTargets.Field Or AttributeTargets.Parameter, AllowMultiple := False)> _
Public Class RequiredAttribute _
    Inherits ValidationAttribute
[AttributeUsageAttribute(AttributeTargets.Property|AttributeTargets.Field|AttributeTargets.Parameter, AllowMultiple = false)]
public class RequiredAttribute : ValidationAttribute

The RequiredAttribute type exposes the following members.

Constructors

  Name Description
Public method RequiredAttribute Initializes a new instance of the RequiredAttribute class.

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Properties

  Name Description
Public property AllowEmptyStrings Gets or sets a value that indicates whether an empty string is allowed.
Public property ErrorMessage Gets or sets the non-localizable error message to display when validation fails. (Inherited from ValidationAttribute.)
Public property ErrorMessageResourceName Gets or sets the property name on the resource type that provides the localizable error message. (Inherited from ValidationAttribute.)
Public property ErrorMessageResourceType Gets or sets the resource type that provides the localizable error message. (Inherited from ValidationAttribute.)
Protected property ErrorMessageString Gets the localized or non-localized error message. (Inherited from ValidationAttribute.)

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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. (Inherited from ValidationAttribute.)
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. (Inherited from ValidationAttribute.)
Protected method IsValid Determines whether the specified object is valid. (Inherited from ValidationAttribute.)
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. (Inherited from ValidationAttribute.)

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Remarks

You apply the RequiredAttribute attribute to a property to specify that the property must contain a value. A validation exception is raised if the property is nulla null reference (Nothing in Visual Basic), an empty string (""), or contains only white-space characters.

Examples

The following example shows how to apply the RequiredAttribute attribute to a property that contains values for a last name.

Public Class Customer
  <Required()> _
  <StringLength(50)> _
  Public Property LastName As String
    'Implement Get and Set logic
  End Property
End Class
public class Customer
{
  [Required]
  [StringLength(50)]
  public string LastName { get; set; }
}

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.