Textarea not validating

Correspondingly, an underlying data value in the view model is automatically updated when the user modifies the bound value in the view.

Provided that the view model has a property called “Name”, you bind it to a Text Box’s Text property in XAML the following way: Besides the path that specifies the name of the property to bind to, the binding must also have a source object.

If you don’t specify a source explicitly by setting the Source property of the binding, it will inherit the Data Context from its parent element to use as its source.

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.

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.

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.

This interface defines two properties that returns a string indicating what is wrong with the object and some property of the object respectively.Once you have created a converter class you will typically add it as a resource in XAML with a unique x: Key attribute and then reference it from the binding as a Static Resource: (string) to a dependency property of type string you don’t necessarily need to use a converter as the default conversion will automatically apply the To String() method on the value of the source property.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.Now that you can see the actual error message, which reads “Value …could not be converted” when the conversion of the string value to an int fails, you may want to customize it.

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