A value converter is used to convert one value to another, by implementing the IValueConverter interface. The values may be of the same type or different types, but require some transformation that is not possible declaratively. These are often powerful because they are written in code, and hence have more logic to control the functionality.
An instance of the converter is generally created in the XAML page and declared as a resource. Then it sets to the controls by using binding expressions with the Converter property.
Whenever the source property changes, the converter returns a different result through the Convert method. The ConvertBack method is called in a two-way binding mode, where the source and target are reversed. In a one-way binding, there's no need to implement ConvertBack and generally we set its body to return an exception, like this—throw new NotImplementedException().