A common requirement for any user interface application that accepts user input is to validate the entered information to ensure that it has the expected format and type for the back-end to be able to accept and persist it.This post is about how data validation works in WPF and the different validation options there are available including implementing custom Validation Rules and using the In a typical WPF application that uses the MVVM (Model-View-View Model) design pattern, a dependency property of a user interface control in a XAML-defined view uses data binding to bind to some data returned by a CLR property of the view model.
Error Template will be displayed on the adorner layer.
Elements in the adorner layer are rendered on top of the rest of the visual elements and they will not be considered when the layout system is measuring and arranging the controls on the adorned element layer.
Errors collection when an exception is thrown in the setter of the source property.
For example, it would be useful if the Age property of the view model was constrained to only accept values between 10 and 100 and threw an exception if the value was outside of this range: interface.
if you are typing a letter into a Text Box bound to a source property of type int: The actual message that is describing the error is stored in the Error Content property of a objects in it, another attached property named Validation. To be able to see the error messages in the view you can replace the default control template that draws the red border around the element with your own custom template by setting the Validation.
Error Template attached property of the control: Note that the Validation.The latter can for example be very useful for bindings in Styles and Control Templates and when you want to bind to some property in a parent element.The Mode property of the , which is the default for the Text property of the Text Box control, the text you type into the Text Box does not update the source property until the control loses focus which happens when you click away from it. the setter for the bound property of the Data Context to get called, as the user is typing into the Text Box you set the Update Source Trigger property to enumeration.Setting the property to this value means that the value of the source property only gets updated when you explicitly call the Binding Expression. You will typically never use this approach in an MVVM application though.If you want to bind a view model property of a specific type to a dependency property in the view of a different type you may need to implement a custom converter class by implementing the interface and setting the Converter property of the binding to an instance of this.A converter class converts data from one type to another during binding by implementing the Convert and Convert Back methods of the mentioned interface.