ValidateValueCallback Delegate

Definition

Namespace:

System.Windows

Assembly:

WindowsBase.dll

Represents a method used as a callback that validates the effective value of a dependency property.

public delegate bool ValidateValueCallback(System::Object ^ value);

public delegate bool ValidateValueCallback(object value);

type ValidateValueCallback = delegate of obj -> bool

Public Delegate Function ValidateValueCallback(value As Object) As Boolean 

Parameters

value

Object

The value to be validated.

Return Value

Boolean

true if the value was validated; false if the submitted value was invalid.

Examples

The following example includes an implementation of this callback to validate a range of values for a custom dependency property. In this case the property value expects an enumeration, and the validation assures that the provided value evaluates to a member of that enumeration.

private static bool ShirtValidateCallback(object value)
{
    ShirtTypes sh = (ShirtTypes) value;
    return (sh==ShirtTypes.None || sh == ShirtTypes.Bowling || sh == ShirtTypes.Dress || sh == ShirtTypes.Rugby || sh == ShirtTypes.Tee);
}

Private Shared Function ShirtValidateCallback(ByVal value As Object) As Boolean
    Dim sh As ShirtTypes = CType(value, ShirtTypes)
    Return (sh=ShirtTypes.None OrElse sh = ShirtTypes.Bowling OrElse sh = ShirtTypes.Dress OrElse sh = ShirtTypes.Rugby OrElse sh = ShirtTypes.Tee)

End Function

Remarks

Callbacks based on this delegate are used by certain signatures of DependencyProperty.Register and related methods, such as RegisterAttached and read-only equivalents. You should use signatures that take the validateValueCallback parameter if you want specific validation of the property value each time that its effective is set. You should then implement this callback such that it performs the actual validation of the proposed value. The callback should return true if the value submitted to the callback is valid, and false otherwise. A false value will produce an exception in the specific portion of the property system where the invalid property set was attempted, so your application should be prepared to handle these exceptions.

Validation callbacks are stored on dependency property identifiers, rather than dependency property metadata. Your validation callback does not have access to a specific instance of a DependencyObject on which the property is set, and can only influence what values are accepted for the property in general. If you need a callback that can change property values based on a specific instance, you should use a combination of a CoerceValueCallback and PropertyChangedCallback callbacks as applied to the property metadata of your property. You might also apply these callbacks to related properties that should influence your property's value. For details, see Dependency Property Callbacks and Validation.

Extension Methods

See also

• DependencyProperty