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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.This interface defines two properties that returns a string indicating what is wrong with the object and some property of the object respectively.Text shows the single character the user just entered.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.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.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.The adorned element in this case is the Text Box control itself and you include an in the control template where you want to leave space for it.
Note that the Text Block will appear on top of any elements that are located right below the Text Box as adorners are always visually on top.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.Besides inheriting and setting the Data Context property on an element directly you can also specify a binding source using the Element Name property, used when you want to bind to some other element, or the Relative Source property.
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.WPF ships with two built-in concrete implementations of the object to the Validation.