![]() Propert圜hanged?.Invoke(this, new Propert圜hangedEventArgs(propertyName)) Protected void OnPropert圜hanged( string propertyName = null) To use the command interface, your ViewModel contains properties of type ICommand: public ICommand M圜ommand = new ObservableCollection() īool SetProperty(ref T storage, T value, string propertyName = null) Public event EventHandler CanExecuteChanged Public bool CanExecute (Object parameter) It is defined instead in the namespace, and consists of two methods and one event: public interface ICommand The interface is not part of Xamarin.Forms. The RefreshCommand property of ListView is also of type ICommand.Īll these commands can be handled within a ViewModel in a manner that doesn't depend on the particular user-interface object in the View. SearchBar defines a SearchCommand property of type ICommand and a SearchCommandParameter property. TextCell and hence, ImageCell, which derives from TextCell.MenuItem and hence, ToolbarItem, which derives from MenuItem.The Command and CommandParameter properties are also defined by the following classes: You can set CommandParameter to arbitrary data to distinguish between multiple buttons if they are all bound to the same ICommand property in the ViewModel. The ViewModel contains code associated with that ICommand property that is executed when the button is clicked. To use the command interface, you define a data binding that targets the Command property of the Button where the source is a property in the ViewModel of type ICommand. To allow a data binding between a Button and a ViewModel, the Button defines two properties: Data bindings are defined between these commands and the Button. The ViewModel itself can contain commands, which are methods that are executed in reaction to a specific activity in the View such as a Button click. The commanding interface provides an alternative approach to implementing commands that is much better suited to the MVVM architecture. These commands are generally signaled by button clicks or finger taps, and traditionally they are processed in the code-behind file in a handler for the Clicked event of the Button or the Tapped event of a TapGestureRecognizer. ![]() Sometimes an application has needs that go beyond these property bindings by requiring the user to initiate commands that affect something in the ViewModel. In the Model-View-ViewModel (MVVM) architecture, data bindings are defined between properties in the ViewModel, which is generally a class that derives from INotifyPropert圜hanged, and properties in the View, which is generally the XAML file.
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