Add a way to lazily bolt on Activated / Deactivated

Author: anaisbetts

ReactiveUI/Activation.cs

@@ -4,6 +4,7 @@
 using System.Reactive;
 using System.Reactive.Disposables;
 using System.Reactive.Linq;
+using System.Reflection;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
@@ -92,4 +93,19 @@ public static IDisposable WhenActivated(this IViewFor This, Action<Action<IDispo
                     }).Item2;
             }, RxApp.SmallCacheLimit);
     }
+
+    public class CanActivateViewFetcher : IActivationForViewFetcher
+    {
+        public int GetAffinityForView(Type view)
+        {
+            return (typeof(ICanActivate).GetTypeInfo().IsAssignableFrom(view.GetType().GetTypeInfo())) ?
+                10 : 0;
+        }
+
+        public Tuple<IObservable<Unit>, IObservable<Unit>> GetActivationForView(IViewFor view)
+        {
+            var ca = view as ICanActivate;
+            return Tuple.Create(ca.Activated, ca.Deactivated);
+        }
+    }
 }

ReactiveUI/Interfaces.cs

@@ -444,6 +444,12 @@ public interface ISupportsActivation
         ViewModelActivator Activator { get; }
     }
 
+    public interface ICanActivate
+    {
+        public IObservable<Unit> Activated { get; }
+        public IObservable<Unit> Deactivated { get; }
+    }
+
     /// <summary>
     /// Allows an additional string to make view resolution more specific than just a type.
     /// </summary>

ReactiveUI/Registrations.cs

@@ -19,6 +19,7 @@ public void Register(Action<Func<object>, Type> registerFunction)
             registerFunction(() => new StringConverter(), typeof(IBindingTypeConverter));
             registerFunction(() => new DefaultViewLocator(), typeof(IViewLocator));
             registerFunction(() => new DummySuspensionHost(), typeof(ISuspensionHost));
+            registerFunction(() => new CanActivateViewFetcher(), typeof(IActivationForViewFetcher));
         }
     }
 }