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Single Member Validators

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The Validation Application Block contains three validators that you can use to validate individual members of types, instead of validating the entire type using attributes or rule sets. While not a common scenario, this technique may be useful when integrating with other frameworks such as WPF and Windows Forms. The three validators are:

  • FieldValueValidator. Use this validator to validate a field of a type.
  • MethodReturnValueValidator. Use this validator to validate the return value of a method of a type.
  • PropertyValueValidator. Use this validator to validate the value of a property of a type.

For example, you can programmatically create a validator for an instance of a class named MyClass that validates the value of a property named MyProperty using a regular expression validator as shown here.

Validator propValidator = new PropertyValueValidator<MyClass>("MyProperty", 
                              new RegexValidator("some-regular-expression"));
MyClass myInstance = new MyClass();
myInstance.MyProperty = "Some value";
ValidationResults results = propValidator.Validate(myInstance);

'Usage
Dim propValidator As New PropertyValueValidator(Of MyClass)("MyProperty", _
                         New RegexValidator("some-regular-expression"))
Dim myInstance As New MyClass()
myInstance.MyProperty = "Some value"
Dim results As ValidationResults = propValidator.Validate(myInstance)

That second parameter to the constructor is the validator to use for the property value. You can also create a composite validator from a combination of validators, and specify this composite validator in the code above. A similar technique can be used with the FieldValueValidator and MethodReturnValueValidator.