Workshop - Improve child navigation performance

src/Artemis.UI.Shared/Routing/Routable/IRoutableHostScreen.cs

@@ -9,5 +9,6 @@ internal interface IRoutableHostScreen : IRoutableScreen
 {
     bool RecycleScreen { get; }
     IRoutableScreen? InternalScreen { get; }
+    IRoutableScreen? InternalDefaultScreen { get; }
     void InternalChangeScreen(IRoutableScreen? screen);
 }

src/Artemis.UI.Shared/Routing/Routable/RoutableHostScreenOfTScreen.cs

@@ -25,7 +25,13 @@ public abstract class RoutableHostScreen<TScreen> : RoutableScreen, IRoutableHos
         protected set => RaiseAndSetIfChanged(ref _recycleScreen, value);
     }
 
+    /// <summary>
+    ///     Gets the screen to show when no other screen is active.
+    /// </summary>
+    public virtual TScreen? DefaultScreen { get; }
+
     IRoutableScreen? IRoutableHostScreen.InternalScreen => Screen;
+    IRoutableScreen? IRoutableHostScreen.InternalDefaultScreen => DefaultScreen;
 
     void IRoutableHostScreen.InternalChangeScreen(IRoutableScreen? screen)
     {

src/Artemis.UI.Shared/Routing/Routable/RoutableHostScreenOfTScreenTParam.cs

@@ -27,7 +27,13 @@ public abstract class RoutableHostScreen<TScreen, TParam> : RoutableScreen<TPara
         protected set => RaiseAndSetIfChanged(ref _recycleScreen, value);
     }
 
+    /// <summary>
+    ///     Gets the screen to show when no other screen is active.
+    /// </summary>
+    public virtual TScreen? DefaultScreen { get; }
+
     IRoutableScreen? IRoutableHostScreen.InternalScreen => Screen;
+    IRoutableScreen? IRoutableHostScreen.InternalDefaultScreen => DefaultScreen;
 
     void IRoutableHostScreen.InternalChangeScreen(IRoutableScreen? screen)
     {

src/Artemis.UI.Shared/Routing/Router/Navigation.cs

@@ -109,12 +109,11 @@ internal class Navigation
             // Navigate the child too
             if (resolution.Child != null)
                 await NavigateResolution(resolution.Child, args, childScreen);
-            // Make sure there is no child
-            else if (childScreen.InternalScreen != null)
-                childScreen.InternalChangeScreen(null);
+            // Without a resolution, navigate to the default screen (which may be null)
+            else if (childScreen.InternalScreen != childScreen.InternalDefaultScreen)
+                childScreen.InternalChangeScreen(childScreen.InternalDefaultScreen);
         }
 
-
         Completed = true;
     }