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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 attached property of the bound element during that step in a previous validation procedure are removed. Errors collection is also cleared when a valid value transfer occurs.WPF ships with two built-in concrete implementations of the object to the Validation.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.Having defined Validation Rule as above if user input is invalid, Text Box will have a red border.Like everything in WPF it is possible to customize it by setting a custom Control Template.
Error Template attached property of the control: Note that the Validation.
This interface defines two properties that returns a string indicating what is wrong with the object and some property of the object respectively.
Below is how the view model would implement the interface – the same interface has been present in Silverlight since version 4 – which enables you to perform server-side validations asynchronously and then notify the view by raising an Errors Changed event once the validations are completed.
This means that you don’t have to use a converter to display a If a user enters an invalid value that cannot be converted to an int and be set as the value for the Age property in the view model in the above example, a validation error will occur and a visual feedback will be provided to the user to indicate this.
By default you will see a red border around the UI element when this happens, e.g.