Validating length of textbox in datagrid

Similarly, it makes it possible to invalidate a property when setting another property and it also supports setting multiple errors per property and custom error objects of some other type than that contains validation errors for the specified property or for the entire entity.

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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.

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 the source of a two-way binding implements the interface and the Validates On Notify Data Errors property of the binding is set to true (which it is by default), the WPF 4.5 binding engine automatically monitors the Errors Changed event and calls the Get Errors method to retrieve the updated errors once the event is raised from the source object provided that the Has Errors property returns true.

Below is an example of a simple service with a single method that validates a username by first querying a database to determine whether it is already in use or not and then checks the length of it and finally determines whether it contains any illegal characters by using a regular expression.In a MVVM WPF application, the view model acts as the window’s Data Context: This means that that all controls inside the window will inherit its Data Context unless some parent element of a control overrides this by setting its own Data Context property.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.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.A converter class converts data from one type to another during binding by implementing the Convert and Convert Back methods of the mentioned interface.

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