fix cache issue for regionmanager

Author: NeverMorewd

src/Lemon.ModuleNavigation.Sample/ViewModels/MainViewModel.cs

@@ -30,8 +30,9 @@ public MainViewModel(IEnumerable<IModule> modules,
         _serviceProvider = serviceProvider;
         _dialogService = dialogService;
         _regionManager = regionManager;
-        // default view
+        // default views for different regions
         _navigationService.RequestViewNavigation("ContentRegion", "ViewAlpha", false);
+        _navigationService.RequestViewNavigation("TransitioningContentRegion", "ViewAlpha", false);
         Modules = new ObservableCollection<IModule>(modules);
         ToViewCommand = ReactiveCommand.Create<string>(content => 
         {

src/Lemon.ModuleNavigation/Core/RegionManager.cs

@@ -9,9 +9,9 @@ public class RegionManager : IRegionManager
     {
         private readonly ConcurrentDictionary<string, IRegion> _regions = [];
         private readonly IServiceProvider _serviceProvider;
-        private readonly ConcurrentStack<NavigationContext> _buffer = [];
-        private readonly ConcurrentSet<IObserver<NavigationContext>> _navigationObservers = new();
-        private readonly ConcurrentSet<IObserver<IRegion>> _regionsObservers = new();
+        private readonly ConcurrentDictionary<string, ConcurrentStack<NavigationContext>> _buffer = [];
+        private readonly ConcurrentSet<IObserver<NavigationContext>> _navigationObservers = [];
+        private readonly ConcurrentSet<IObserver<IRegion>> _regionsObservers = [];
         public RegionManager(IServiceProvider serviceProvider)
         {
             _serviceProvider = serviceProvider;
@@ -27,7 +27,18 @@ public void RequestNavigate(string regionName, string viewName, bool requestNew,
             }
             else
             {
-                _buffer.Push(context);
+                _buffer.AddOrUpdate(regionName,
+                    key => 
+                    {
+                        var stack = new ConcurrentStack<NavigationContext>();
+                        stack.Push(context);
+                        return stack;
+                    }, 
+                    (key, value) =>
+                    {
+                        value.Push(context);
+                        return value;
+                    });
             }
         }
 
@@ -36,11 +47,14 @@ public void AddRegion(string regionName, IRegion region)
             if (_regions.TryAdd(regionName, region))
             {
                 ToRegionsObservers(region);
-                if (_buffer.TryPop(out var context))
+
+                if (_buffer.TryGetValue(regionName, out var navigationContexts))
                 {
-                    region.Activate(context);
-                    ToNavigationObservers(context);
-                    _buffer.Clear();
+                    if (navigationContexts.TryPop(out var context))
+                    {
+                        region.Activate(context);
+                        ToNavigationObservers(context);
+                    }
                 }
             }
             else