![]() ![]() The following value converter converts a bool from the source to an object of type T for the target: public class BoolToObjectConverter : IValueConverter Value converter classes can have properties and generic parameters. If the conversion being performed is different for different cultures, use the culture parameter for this purpose. In this case the value converter can use the targetType argument to perform a conversion for the correct type. Sometimes, value converters are used with data bindings of different target types. The expected type of each method's return value is given by the targetType parameter. The Convert and ConvertBack methods can use the as or is operators with the value parameter, or can call GetType on that parameter to determine its type, and then do something appropriate. You can write value converters to be more generalized and to accept several different types of data. If that is not the case, a runtime exception will occur. Similarly, the ConvertBack method assumes that the value argument is of type bool and the return value is int. The Convert method shown above assumes that the value argument is of type int and the return value must be of type bool. If you know that a value converter will only be used in OneWay bindings, then the ConvertBack method can simply return null. If that Length property is not 0, the value converter returns true and the Button is enabled: The data-binding source is the Length property of the Text property of the corresponding Entry. Each Button contains a data binding on its IsEnabled property. If nothing has been typed into the Entry, the Button should be disabled. The Text property of each Entry is initialized to an empty string, because the Text property is null by default, and the data binding will not work in that case. This example demonstrates a common need when a Button performs an operation based on text that the user types into an Entry view. If a value converter is used in multiple pages of your application, you can instantiate it in the application-level resource dictionary. It is very common to share data converters among multiple data bindings on the page. It's then referenced with a StaticResource markup extension to set the Converter property in two data bindings. In this example, the IntToBoolConverter is instantiated in the page's resource dictionary. The following example demonstrates how to use this value converter in a data binding: If a data binding also includes a StringFormat setting, the value converter is invoked before the result is formatted as a string. ConvertBack performs the opposite conversion: It assumes the value parameter is a bool from the target, and converts it to an int return value for the source. The ConvertBack method is called when data moves from the target to the source in TwoWay or OneWayToSource bindings. The method shown here casts the value parameter to an int and then compares it with 0 for a bool return value. The method must return a value of the type of the data-binding target. The value parameter is the object or value from the data-binding source. The Convert method is called when data moves from the source to the target in OneWay or TwoWay bindings. This class becomes part of the data binding. You then set an instance of this class to the Converter property of the Binding class or to the Converter property of the Binding markup extension. Public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) Public object Convert(object value, Type targetType, object parameter, CultureInfo culture) This can be achieved with a class that implements the IValueConverter interface: public class IntToBoolConverter : IValueConverter You want this data binding to produce a false value when the integer source is equal to 0, and true otherwise. Suppose you want to define a data binding where the source property is of type int but the target property is a bool. Classes that implement IValueConverter are called value converters, but they are also often referred to as binding converters or binding value converters. For other types of conversions, you need to write some specialized code in a class that implements the IValueConverter interface. In the String formatting article, you saw how you can use the StringFormat property of a data binding to convert any type into a string. When that is not the case, a type conversion must take place. This transfer is straightforward when the source and target properties are of the same type, or when one type can be converted to the other type through an implicit conversion. NET Multi-platform App UI (.NET MAUI) data bindings usually transfer data from a source property to a target property, and in some cases from the target property to the source property.
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