Add component for managing a DI scope

Fixes: #5496
Fixes: #10448

This change adds a *utility* base class that encourages you to do the
right thing when you need to interact with a disposable scoped or
transient service.

This solution ties the lifetime of a DI scope and a service to a
component instance. Note that this is not recursive - we expect users to
pass services like this around (or as cascading values) if the design
dictates it.

src/Components/Components/ref/Microsoft.AspNetCore.Components.netstandard2.0.cs

@@ -302,6 +302,19 @@ namespace Microsoft.AspNetCore.Components
         public NavigationException(string uri) { }
         public string Location { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
     }
+    public abstract partial class OwningComponentBase : Microsoft.AspNetCore.Components.ComponentBase, System.IDisposable
+    {
+        protected OwningComponentBase() { }
+        protected bool IsDisposed { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
+        protected System.IServiceProvider ScopedServices { get { throw null; } }
+        protected virtual void Dispose(bool disposing) { }
+        void System.IDisposable.Dispose() { }
+    }
+    public abstract partial class OwningComponentBase<TService> : Microsoft.AspNetCore.Components.OwningComponentBase, System.IDisposable
+    {
+        protected OwningComponentBase() { }
+        protected TService Service { get { throw null; } }
+    }
     public partial class PageDisplay : Microsoft.AspNetCore.Components.IComponent
     {
         public PageDisplay() { }

src/Components/Components/src/OwningComponentBase.cs

@@ -0,0 +1,100 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Microsoft.AspNetCore.Components
+{
+    /// <summary>
+    /// A base class that creates a service provider scope.
+    /// </summary>
+    /// <remarks>
+    /// Use the <see cref="OwningComponentBase"/> class as a base class to author components that control
+    /// the lifetime of a service provider scope. This is useful when using a transient or scoped service that
+    /// requires disposal such as a repository or database abstraction. Using <see cref="OwningComponentBase"/>
+    /// as a base class ensures that the service provider scope is disposed with the component.
+    /// </remarks>
+    public abstract class OwningComponentBase : ComponentBase, IDisposable
+    {
+        private IServiceScope _scope;
+
+        [Inject] IServiceScopeFactory ScopeFactory { get; set; }
+
+        /// <summary>
+        /// Gets a value determining if the component and associated services have been disposed.
+        /// </summary>
+        protected bool IsDisposed { get; private set; }
+
+        /// <summary>
+        /// Gets the scoped <see cref="IServiceProvider"/> that is associated with this component.
+        /// </summary>
+        protected IServiceProvider ScopedServices
+        {
+            get
+            {
+                if (ScopeFactory == null)
+                {
+                    throw new InvalidOperationException("Services cannot be accessed before the component is initialized.");
+                }
+
+                if (IsDisposed)
+                {
+                    throw new ObjectDisposedException(GetType().Name);
+                }
+
+                _scope ??= ScopeFactory.CreateScope();
+                return _scope.ServiceProvider;
+            }
+        }
+
+        void IDisposable.Dispose()
+        {
+            if (!IsDisposed)
+            {
+                _scope?.Dispose();
+                _scope = null;
+                Dispose(disposing: true);
+                IsDisposed = true;
+            }
+        }
+
+        /// <inheritdoc />
+        protected virtual void Dispose(bool disposing)
+        {
+        }
+    }
+
+    /// <summary>
+    /// A base class that creates a service provider scope, and resolves a service of type <typeparamref name="TService"/>.
+    /// </summary>
+    /// <typeparam name="TService">The service type.</typeparam>
+    /// <remarks>
+    /// Use the <see cref="OwningComponentBase{TService}"/> class as a base class to author components that control
+    /// the lifetime of a service or multiple services. This is useful when using a transient or scoped service that
+    /// requires disposal such as a repository or database abstraction. Using <see cref="OwningComponentBase{TService}"/>
+    /// as a base class ensures that the service and relates services that share its scope are disposed with the component.
+    /// </remarks>
+    public abstract class OwningComponentBase<TService> : OwningComponentBase, IDisposable
+    {
+        private TService _item;
+
+        /// <summary>
+        /// Gets the <typeparamref name="TService"/> that is associated with this component.
+        /// </summary>
+        protected TService Service
+        {
+            get
+            {
+                if (IsDisposed)
+                {
+                    throw new ObjectDisposedException(GetType().Name);
+                }
+
+                // We cache this because we don't know the lifetime. We have to assume that it could be transient.
+                _item ??= ScopedServices.GetRequiredService<TService>();
+                return _item;
+            }
+        }
+    }
+}

src/Components/Components/test/OwningComponentBaseTest.cs

@@ -0,0 +1,61 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Dynamic;
+using System.Linq;
+using Microsoft.AspNetCore.Components.RenderTree;
+using Microsoft.AspNetCore.Components.Test.Helpers;
+using Microsoft.Extensions.DependencyInjection;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Components
+{
+    public class OwningComponentBaseTest
+    {
+        [Fact]
+        public void CreatesScopeAndService()
+        {
+            var services = new ServiceCollection();
+            services.AddSingleton<Counter>();
+            services.AddTransient<MyService>();
+            var serviceProvider = services.BuildServiceProvider();
+
+            var counter = serviceProvider.GetRequiredService<Counter>();
+            var renderer = new TestRenderer(serviceProvider);
+            var component1 = renderer.InstantiateComponent<MyOwningComponent>();
+
+            Assert.NotNull(component1.MyService);
+            Assert.Equal(1, counter.CreatedCount);
+            Assert.Equal(0, counter.DisposedCount);
+
+            ((IDisposable)component1).Dispose();
+            Assert.Equal(1, counter.CreatedCount);
+            Assert.Equal(1, counter.DisposedCount);
+        }
+
+        private class Counter
+        {
+            public int CreatedCount { get; set; }
+            public int DisposedCount { get; set; }
+        }
+
+        private class MyService : IDisposable
+        {
+            public MyService(Counter counter)
+            {
+                Counter = counter;
+                Counter.CreatedCount++;
+            }
+
+            public Counter Counter { get; }
+
+            void IDisposable.Dispose() => Counter.DisposedCount++;
+        }
+
+        private class MyOwningComponent : OwningComponentBase<MyService>
+        {
+            public MyService MyService => Service;
+        }
+    }
+}