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:

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:

listView.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="listView" 
                                 ItemsSource="{Binding Source}">
    <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.Maui.Controls.Compatibility"

See Also

In this article
Not finding the help you need?