Implement a generic version of the EventToCommandBehavior

src/CommunityToolkit/Xamarin.CommunityToolkit.UnitTests/Behaviors/EventToCommandBehaviorGeneric_Tests.cs

@@ -0,0 +1,170 @@
+using System;
+using System.Reflection;
+using Xamarin.CommunityToolkit.Behaviors;
+using Xamarin.CommunityToolkit.Converters;
+using Xamarin.CommunityToolkit.UnitTests.Mocks;
+using Xamarin.Forms;
+using NUnit.Framework;
+
+namespace Xamarin.CommunityToolkit.UnitTests.Behaviors
+{
+	public class EventToCommandBehaviorGeneric_Tests
+	{
+		[SetUp]
+		public void Setup() => Device.PlatformServices = new MockPlatformServices();
+
+		[Test]
+		public void ArgumentExceptionIfSpecifiedEventDoesNotExist()
+		{
+			var listView = new ListView();
+			var behavior = new EventToCommandBehavior<Coffee>
+			{
+				EventName = "Wrong Event Name"
+			};
+			Assert.Throws<ArgumentException>(() => listView.Behaviors.Add(behavior));
+		}
+
+		[Test]
+		public void NoExceptionIfSpecifiedEventExists()
+		{
+			var listView = new ListView();
+			var behavior = new EventToCommandBehavior<Coffee>
+			{
+				EventName = nameof(ListView.ItemTapped)
+			};
+			listView.Behaviors.Add(behavior);
+		}
+
+		[Test]
+		public void NoExceptionIfAttachedToPage()
+		{
+			var page = new ContentPage();
+			var behavior = new EventToCommandBehavior<Coffee>
+			{
+				EventName = nameof(Page.Appearing)
+			};
+			page.Behaviors.Add(behavior);
+		}
+
+		[Test]
+		public void NoExceptionWhenTheEventArgsAreNotNull()
+		{
+			var vm = new ViewModelCoffe();
+			var behavior = new EventToCommandBehavior<Coffee>
+			{
+				EventName = nameof(ListView.ItemTapped),
+				EventArgsConverter = new ItemSelectedEventArgsConverter(),
+				Command = vm.SelectedCommand
+			};
+
+			Assert.Null(vm.CoffeeName);
+			var coffe = new Coffee { Id = 1, Name = "Café" };
+			var eventArgs = new SelectedItemChangedEventArgs(coffe, 1);
+
+			var notNullArgs = new object?[] { null, eventArgs };
+
+			TriggerEventToCommandBehavior(behavior, notNullArgs);
+
+			Assert.AreEqual(coffe.Name, vm.CoffeeName);
+		}
+
+		[Test]
+		public void NoExceptionWhenTheEventArgsAreNotNull_InheritedType()
+		{
+			var vm = new ViewModelCoffe();
+			var behavior = new EventToCommandBehavior<Coffee>
+			{
+				EventName = nameof(ListView.ItemTapped),
+				EventArgsConverter = new ItemSelectedEventArgsConverter(),
+				Command = vm.SelectedCommand
+			};
+
+			Assert.Null(vm.CoffeeName);
+			var coffe = new Starbucks { Id = 1, Name = "Latte" };
+			var eventArgs = new SelectedItemChangedEventArgs(coffe, 1);
+
+			var notNullArgs = new object?[] { null, eventArgs };
+
+			TriggerEventToCommandBehavior(behavior, notNullArgs);
+
+			Assert.AreEqual(coffe.Name, vm.CoffeeName);
+		}
+
+		[Test]
+		public void ParameterOfTypeInt()
+		{
+			var vm = new ViewModelCoffe();
+			var behavior = new EventToCommandBehavior<int>
+			{
+				EventName = nameof(ListView.ItemTapped),
+				Command = vm.SelectedCommand,
+				CommandParameter = 2
+			};
+
+			var nullArgs = new object?[] { null, null };
+
+			TriggerEventToCommandBehavior(behavior, nullArgs);
+		}
+
+		[Test]
+		public void NoExceptionWhenTheSelectedItemIsNull()
+		{
+			var vm = new ViewModelCoffe();
+			var behavior = new EventToCommandBehavior<Coffee>
+			{
+				EventName = nameof(ListView.ItemTapped),
+				EventArgsConverter = new ItemSelectedEventArgsConverter(),
+				Command = vm.SelectedCommand
+			};
+
+			Assert.Null(vm.CoffeeName);
+			var coffeNull = default(Coffee);
+			var notNullArgs = new object?[] { null, new SelectedItemChangedEventArgs(coffeNull, -1) };
+
+			TriggerEventToCommandBehavior(behavior, notNullArgs);
+
+			Assert.Null(vm.CoffeeName);
+		}
+
+		static void TriggerEventToCommandBehavior<T>(EventToCommandBehavior<T> eventToCommand, object?[] args)
+		{
+			var method = eventToCommand.GetType().GetMethod("OnTriggerHandled", BindingFlags.Instance | BindingFlags.NonPublic);
+			method?.Invoke(eventToCommand, args);
+		}
+
+		class Starbucks : Coffee
+		{
+		}
+
+		class Coffee
+		{
+			public int Id { get; set; }
+
+			public string Roaster { get; set; } = string.Empty;
+
+			public string? Name { get; set; }
+
+			public string Image { get; set; } = string.Empty;
+		}
+
+		class ViewModelCoffe
+		{
+			public Command<Coffee> SelectedCommand { get; set; }
+
+			public string? CoffeeName { get; set; }
+
+			public ViewModelCoffe()
+			{
+				SelectedCommand = new Command<Coffee>(Selected);
+			}
+
+			void Selected(Coffee coffee)
+			{
+				if (coffee == null)
+					return;
+
+				CoffeeName = coffee?.Name;
+			}
+		}
+	}
+}

src/CommunityToolkit/Xamarin.CommunityToolkit/Behaviors/EventToCommandBehaviorGeneric.shared.cs

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+using System;
+
+namespace Xamarin.CommunityToolkit.Behaviors
+{
+	/// <summary>
+	/// This <see cref="EventToCommandBehavior"/> cast the sender object to a specific type defined by the user.
+	/// </summary>
+	/// <typeparam name="TType">The type that you want to receive in your <see cref="Xamarin.Forms.Command"/> </typeparam>
+	public sealed class EventToCommandBehavior<TType> : EventToCommandBehavior
+	{
+		protected override void OnTriggerHandled(object? sender = null, object? eventArgs = null)
+		{
+			var parameter = CommandParameter
+				?? EventArgsConverter?.Convert(eventArgs, typeof(object), null, null)
+				?? eventArgs;
+
+			if (parameter is not TType)
+			{
+				// changing it to the default value to avoid a cast exception
+				parameter = default(TType);
+			}
+
+			var command = Command;
+			if (command?.CanExecute(parameter) ?? false)
+				command.Execute(parameter);
+		}
+	}
+}