Articolo
11/18/2011

RequiredAttribute Class

Microsoft Silverlight will reach end of support after October 2021. Learn more.

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
	RequiredAttribute	Initializes a new instance of the RequiredAttribute class.

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Properties

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

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Methods

	Name	Description
	Equals	Infrastructure. Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute.)
	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.)
	FormatErrorMessage	Applies formatting to the error message. (Inherited from ValidationAttribute.)
	GetHashCode	Returns the hash code for this instance. (Inherited from Attribute.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	GetValidationResult	Determines whether the specified object is valid and returns an object that includes the results of the validation check. (Inherited from ValidationAttribute.)
	IsValid	Determines whether the specified object is valid. (Inherited from ValidationAttribute.)
	Match	When overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	ToString	Returns a string that represents the current object. (Inherited from Object.)
	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.

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