Commands

The Command design-pattern is widely used in the XAML and MVVM world. RadListView strictly follows the Command design-pattern best practices and provides an intuitive and easy-to-use set of APIs that allow you to control various aspects of RadListView’s behavior.

RadListView exposes a Commands collection that allows you to register custom commands with each control’s instance through the RadListView.Commands property:

• Commands: Gets the collection with all the custom commands registered with the CommandService. Custom commands have higher priority than the built-in (default) ones.

CommandId Enumeration

All predefined commands within a RadListView instance are identified by a member of the CommandId enumeration. This member is actually the key that relates a command instance to a particular action/routine within the owning ListView.

To register a custom command within a RadListView instance you can:

• Inherit from the ListViewCommand class and override its CanExecute and Execute methods.
• Use the ListViewUserCommand class and bind its Command property to a Command in your ViewModel.

In both cases, you need to set the Id property of the new command so that it can be properly associated with the desired action/event.

Following are the members of the CommandId enumerations:

• ItemTap
• ItemSwiping
• ItemSwipeCompleted
• ItemSwipeStarting
• PullToRefreshRequested
• SelectionChanged
• LoadOnDemand
• ItemHold
• GroupHeaderTap
• ReorderStarting
• ReorderEnded

These actions correspond to the events exposed by RadListView. For more details, see the Events topic.

For each of the available commands, there is a context object of type [CommandId]CommandContext, for example, ItemTapCommandContext, ItemHoldCommandContext, etc. The context object is passed as a parameter in its Execute method and provides information identical to the corresponding event's args.

Inheriting from ListViewCommand

To demonstrate inheriting from ListViewCommand, the following example handles the ItemTap action as a Command:

1. Create a class that inherits from ListViewCommand and set its Id property. Then override the CanExecute and Execute methods:

   public class ItemTappedUserCommand : ListViewCommand
   {
   public ItemTappedUserCommand()
   {
       Id = CommandId.ItemTap;
   }
   public override bool CanExecute(object parameter)
   {
       return true;
   }
   public override void Execute(object parameter)
   {
       var tappedItem = (parameter as ItemTapCommandContext).Item;
       //add your logic here
       Application.Current.MainPage.DisplayAlert("", "You've selected " + tappedItem, "OK");
   }
   }
   

2. Add the custom command to the Commands collection of the RadListView instance:

   listView1.Commands.Add(new ItemTappedUserCommand());
   

   Binding ListViewUserCommand

With the ListViewUserCommand binding approach, you can directly handle the custom commands in the ViewModel. Here is a quick example:

1. Add the custom command to the ViewModel:

   public class ViewModel
   {
   public ViewModel()
   {
       this.Source = new List<string> {"Tom", "Anna", "Peter", "Teodor", "Martin"};
       this.ItemTapCommand = new Command<ItemTapCommandContext>(this.ItemTapped);
   }
   private void ItemTapped(ItemTapCommandContext context)
   {
       var tappedItem = context.Item;
       //add your logic here
       Application.Current.MainPage.DisplayAlert("", "You've selected " + tappedItem, "OK");
   }
   public List<string> Source { get; set; }
   public ICommand ItemTapCommand { get; set; }
   }
   

2. Bind the ItemTapCommand through the predefined ListViewUserCommand command. Its Id property is used to map the command to the corresponding action with the control:

   <telerikDataControls:RadListView x:Name="listView2" ItemsSource="{Binding Source}" AutomationId="bottomListView">
   <telerikDataControls:RadListView.BindingContext>
       <local:ViewModel />
   </telerikDataControls:RadListView.BindingContext>
   <telerikDataControls:RadListView.Commands>
       <telerikListViewCommands:ListViewUserCommand Id="ItemTap" Command="{Binding ItemTapCommand}" />
   </telerikDataControls:RadListView.Commands>
   </telerikDataControls:RadListView>
   

3. Define the telerikListViewCommands:

       xmlns:telerikListViewCommands="clr-namespace:Telerik.XamarinForms.DataControls.ListView.Commands;assembly=Telerik.XamarinForms.DataControls"
   ```
   

   See Also

   • Events
   • Selection
   • Reordering