[Proposal] `ItemSelectedEventArgs` Converter

ItemSelectedEventArgs Converter

• Proposed
• Prototype
• Implementation
  • iOS Support
  • Android Support
  • macOS Support
  • Windows Support
• Unit Tests
• Sample
• Documentation

Summary

The ItemSelectedEventArgsConverter is a converter that allows users to extract the SelectedItem value from an SelectedItemChangedEventArgs object. It can subsequently be used in combination with EventToCommandBehavior

Detailed Design

ItemSelectedEventArgsConverter.shared.cs

public class ItemSelectedEventArgsConverter : ValueConverterExtension, IValueConverter
{
  public object? Convert(object? value, Type? targetType, object? parameter, CultureInfo? culture)
  {
    if (value == null)
      return null;
    
    return value is SelectedItemChangedEventArgs selectedItemChangedEventArgs
		? selectedItemChangedEventArgs.SelectedItem
		: throw new ArgumentException("Expected value to be of type SelectedItemChangedEventArgs", nameof(value));
  }

  public object? ConvertBack(object? value, Type? targetType, object? parameter, CultureInfo? culture) => throw new NotImplementedException();
}

Usage Syntax

XAML Usage

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:xct="http://xamarin.com/schemas/2020/toolkit"
             x:Class="MyLittleApp.MainPage">

    <ContentPage.Resources>
        <ResourceDictionary>
            <xct:ItemSelectedEventArgsConverter x:Key="ItemSelectedEventArgsConverter" />
        </ResourceDictionary>
    </ContentPage.Resources>

    <ListView ItemsSource="{Binding Items}" HasUnevenRows="True">

        <ListView.Behaviors>
            <xct:EventToCommandBehavior EventName="ItemSelected"
                                              Command="{Binding ItemSelectedCommand}"
                                              EventArgsConverter="{StaticResource ItemSelectedEventArgsConverter}" />
        </ListView.Behaviors>

    </ListView>
</ContentPage>

C# Usage

class MyPage : ContentPage
{
  public MyPage()
  {
    var behavior = new EventToCommandBehavior
    {
      EventName = nameof(ListView.ItemSelected),
      EventArgsConverter = new ItemSelectedEventArgsConverter()
    };
    behavior.SetBinding(EventToCommandBehavior.CommandProperty, nameof(ViewModel.ItemSelectedCommand);

    var listView = new ListView { HasUnevenRows = true }.Bind(ListView.ItemsSource, nameof(ViewModel.Items));
    listView.Behaviors.Add(behavior);

    Content = listView;
  }
}

[bijington]

Thanks again @CliffAgius 3 Proposals closed 😄

[CliffAgius]

Can I have the docs for this one assigned to me please. 💪