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RequiredAttribute Class

Specifies that a data field value is required.

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)

[AttributeUsageAttribute(AttributeTargets::Property|AttributeTargets::Field|AttributeTargets::Parameter, AllowMultiple = false)]
public ref class RequiredAttribute : public ValidationAttribute

The RequiredAttribute type exposes the following members.

  NameDescription
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsRequiredAttributeInitializes a new instance of the RequiredAttribute class.
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  NameDescription
Public propertySupported by Portable Class LibrarySupported in .NET for Windows Store appsAllowEmptyStringsGets or sets a value that indicates whether an empty string is allowed.
Public propertySupported by Portable Class LibrarySupported in .NET for Windows Store appsErrorMessageGets or sets an error message to associate with a validation control if validation fails. (Inherited from ValidationAttribute.)
Public propertySupported by Portable Class LibrarySupported in .NET for Windows Store appsErrorMessageResourceNameGets or sets the error message resource name to use in order to look up the ErrorMessageResourceType property value if validation fails. (Inherited from ValidationAttribute.)
Public propertySupported by Portable Class LibrarySupported in .NET for Windows Store appsErrorMessageResourceTypeGets or sets the resource type to use for error-message lookup if validation fails. (Inherited from ValidationAttribute.)
Protected propertySupported by Portable Class LibrarySupported in .NET for Windows Store appsErrorMessageStringGets the localized validation error message. (Inherited from ValidationAttribute.)
Public propertyRequiresValidationContextGets a value that indicates whether the attribute requires validation context. (Inherited from ValidationAttribute.)
Public propertyTypeIdWhen implemented in a derived class, gets a unique identifier for this Attribute. (Inherited from Attribute.)
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  NameDescription
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsEqualsInfrastructure. Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute.)
Protected methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsFormatErrorMessageApplies formatting to an error message, based on the data field where the error occurred. (Inherited from ValidationAttribute.)
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsGetHashCodeReturns the hash code for this instance. (Inherited from Attribute.)
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsGetValidationResultChecks whether the specified value is valid with respect to the current validation attribute. (Inherited from ValidationAttribute.)
Public methodIsDefaultAttributeWhen overridden in a derived class, indicates whether the value of this instance is the default value for the derived class. (Inherited from Attribute.)
Public methodIsValid(Object)Checks that the value of the required data field is not empty. (Overrides ValidationAttribute::IsValid(Object).)
Protected methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsIsValid(Object, ValidationContext)Validates the specified value with respect to the current validation attribute. (Inherited from ValidationAttribute.)
Public methodMatchWhen overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute.)
Protected methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsToStringReturns a string that represents the current object. (Inherited from Object.)
Public methodSupported by Portable Class LibrarySupported in .NET for Windows Store appsValidate(Object, ValidationContext)Validates the specified object. (Inherited from ValidationAttribute.)
Public methodValidate(Object, String)Validates the specified object. (Inherited from ValidationAttribute.)
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  NameDescription
Explicit interface implemetationPrivate method_Attribute::GetIDsOfNamesMaps a set of names to a corresponding set of dispatch identifiers. (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute::GetTypeInfoRetrieves the type information for an object, which can be used to get the type information for an interface. (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute::GetTypeInfoCountRetrieves the number of type information interfaces that an object provides (either 0 or 1). (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute::InvokeProvides access to properties and methods exposed by an object. (Inherited from Attribute.)
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The RequiredAttribute attribute specifies that when a field on a form is validated, the field must contain a value. A validation exception is raised if the property is nullptr, contains an empty string (""), or contains only white-space characters.

NoteNote

If the MVC data model or entity partial class contains a field that is annotated with the RequiredAttribute attribute, but the page does not contain the property, an error is not raised. Validation occurs only for fields that are submitted to the server.

A Visual Studio project with source code is available to accompany this topic: Download.

The following example uses the RequiredAttribute attribute to override the database schema rule that allows a data field to be empty. The example performs the following steps:

  • Implements a metadata partial class and the associated metadata class.

  • In the associated metadata class, it applies the RequiredAttribute attribute, which specifies the following requirements:

    • The Title data field cannot be empty. If validation fails, the code in the example throws a validation exception and displays an error message. The error message is specified at the time that the attribute is applied to the data field.

    • The MiddleName data field cannot be empty. If validation fails, the code in the example throws a validation exception and displays an error message.

No code example is currently available or this language may not be supported.

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5 SP1

.NET Framework Client Profile

Supported in: 4

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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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