Avalonia/tests/Avalonia.ReactiveUI.UnitTests/AvaloniaActivationForViewFetcherTest.cs

using System;
using System.Reactive.Concurrency;
using System.Reactive.Disposables;
using Avalonia.Controls;
using Avalonia.Rendering;
using Avalonia.Platform;
using Avalonia;
using ReactiveUI;
using DynamicData;
using Xunit;
using Splat;

namespace Avalonia 
{
    public class AvaloniaActivationForViewFetcherTest
    {
        public class TestUserControl : UserControl, IActivatable { }

        public class FakeRenderDecorator : Decorator, IRenderRoot
        {
            public Size ClientSize => new Size(100, 100);

            public IRenderer Renderer { get; }

            public double RenderScaling => 1;

            public IRenderTarget CreateRenderTarget() => null;

            public void Invalidate(Rect rect) { }

            public Point PointToClient(Point point) => point;

            public Point PointToScreen(Point point) => point;
        }

        public class TestUserControlWithWhenActivated : UserControl, IActivatable
        {
            public bool Active { get; private set; }

            public TestUserControlWithWhenActivated()
            {
                this.WhenActivated(disposables => {
                    Active = true;
                    Disposable
                        .Create(() => Active = false)
                        .DisposeWith(disposables);
                });
            }
        }

        [Fact]
        public void VisualElementIsActivatedAndDeactivated()
        {
            var userControl = new TestUserControl();
            var activationForViewFetcher = new AvaloniaActivationForViewFetcher();

            activationForViewFetcher
                .GetActivationForView(userControl)
                .ToObservableChangeSet(scheduler: ImmediateScheduler.Instance)
                .Bind(out var activated)
                .Subscribe();

            var fakeRenderedDecorator = new FakeRenderDecorator();
            fakeRenderedDecorator.Child = userControl;
            Assert.True(activated[0]);
            Assert.Equal(1, activated.Count);

            fakeRenderedDecorator.Child = null;
            Assert.True(activated[0]);
            Assert.False(activated[1]);
            Assert.Equal(2, activated.Count);
        }

        [Fact]
        public void ActivationForViewFetcherShouldSupportWhenActivated()
        {
            var locator = new ModernDependencyResolver();
            locator.InitializeSplat();
            locator.InitializeReactiveUI();
            locator.RegisterConstant(new AvaloniaActivationForViewFetcher(), typeof(IActivationForViewFetcher));
            using (locator.WithResolver()) 
            {
                var userControl = new TestUserControlWithWhenActivated();
                Assert.False(userControl.Active);

                var fakeRenderedDecorator = new FakeRenderDecorator();
                fakeRenderedDecorator.Child = userControl;
                Assert.True(userControl.Active);

                fakeRenderedDecorator.Child = null;
                Assert.False(userControl.Active);
            }
        }
    }
}