Added option to create service scopes per window or dialog by overriding the WindowManager.CreateScope() method

Source/IWindowScope.cs

@@ -0,0 +1,45 @@
+using System;
+
+namespace Nuclex.Windows.Forms {
+
+  /// <summary>Constructs views and view model in a scope</summary>
+  /// <remarks>
+  ///   <para>
+  ///     By default the <see cref="WindowManager" /> uses its own
+  ///     <see cref="WindowManager.CreateInstance" /> method to construct views
+  ///     and view models via <see cref="Activator.CreateInstance(Type)" />,
+  ///     which is enough to create forms (which the Windows Forms designer already
+  ///     requires to have parameterless constructors) and view models, so long as
+  ///     they also have parameterless constructors.
+  ///   </para>
+  ///   <para>
+  ///     To support dependency injection via constructor parameters, you can
+  ///     inherit from the <see cref="WindowManager" /> and provide your own override
+  ///     of <see cref="WindowManager.CreateInstance" /> that constructs the required
+  ///     instance via your dependency injector. This is decent until you have multiple
+  ///     view models all accessing the same resource (i.e. a database) via threads.
+  ///   </para>
+  ///   <para>
+  ///     In this final case, &quot;scopes&quot; have become a common solution. Each
+  ///     scope has access to singleton services (these exist for the lifetime of
+  ///     the entire application), but there are also scoped services which will have
+  ///     new instances constructed within each scope. By implementing the
+  ///     <see cref="WindowManager.CreateWindowScope" /> method, you can make
+  ///     the window manager set up an implicit scope per window or dialog.
+  ///   </para>
+  /// </remarks>
+  public interface IWindowScope : IDisposable {
+
+    /// <summary>Creates an instance of the specified type in the scope</summary>
+    /// <param name="type">Type an instance will be created of</param>
+    /// <returns>The created instance</returns>
+    /// <remarks>
+    ///   Use this to wire up your dependency injection container. By default,
+    ///   the Activator class will be used to create instances which only works
+    ///   if all of your view models are concrete classes.
+    /// </remarks>
+    object CreateInstance(Type type);
+
+  }
+
+} // namespace Nuclex.Windows.Forms

Source/WindowManager.cs

@@ -39,6 +39,36 @@ namespace Nuclex.Windows.Forms {
 #endif
   public class WindowManager : Observable, IWindowManager {
 
+    #region class WindowManagerScope
+
+    /// <summary>Global scope that uses the WindowManager's CreateInstance()</summary>
+    public class WindowManagerScope : IWindowScope {
+
+      /// <summary>Initializes a new global window scope</summary>
+      /// <param name="windowManager">
+      ///   Window manager whose CreateInstance() method will be used
+      /// </param>
+      public WindowManagerScope(WindowManager windowManager) {
+        this.windowManager = windowManager;
+      }
+
+      /// <summary>Creates an instance of the specified type in the scope</summary>
+      /// <param name="type">Type an instance will be created of</param>
+      /// <returns>The created instance</returns>
+      object IWindowScope.CreateInstance(Type type) {
+        return this.windowManager.CreateInstance(type);
+      }
+
+      /// <summary>Does nothing because this is the global fallback scope</summary>
+      void IDisposable.Dispose() {}
+
+      /// <summary>WindowManager whose CreateInstance() method will be wrapped</summary>
+      private WindowManager windowManager;
+
+    }
+
+    #endregion // class WindwoManagerScope
+
     #region class CancellableDisposer
 
     /// <summary>Disposes an object that potentially implements IDisposable</summary>
@@ -91,6 +121,7 @@ namespace Nuclex.Windows.Forms {
 
       this.rootWindowActivatedDelegate = rootWindowActivated;
       this.rootWindowClosedDelegate = rootWindowClosed;
+      this.windowManagerAsScope = new WindowManagerScope(this);
       this.viewTypesForViewModels = new ConcurrentDictionary<Type, Type>();
     }
 
@@ -193,8 +224,13 @@ namespace Nuclex.Windows.Forms {
     public virtual Control CreateView<TViewModel>(
       TViewModel viewModel = null
     ) where TViewModel : class {
+      Control viewControl;
+      {
         Type viewType = LocateViewForViewModel(typeof(TViewModel));
-      Control viewControl = (Control)CreateInstance(viewType);
+
+        IWindowScope scope = CreateWindowScope();
+        using(var scopeDisposer = new CancellableDisposer(scope)) {
+          viewControl = (Control)scope.CreateInstance(viewType);
           using(var viewDisposer = new CancellableDisposer(viewControl)) {
 
             // Create a view model if none was provided, and in either case assign
@@ -203,16 +239,16 @@ namespace Nuclex.Windows.Forms {
               IView viewControlAsView = viewControl as IView;
               if(viewModel == null) { // No view model provided, create one
                 if(viewControlAsView == null) { // View doesn't implement IView
-              viewModel = (TViewModel)CreateInstance(typeof(TViewModel));
+                  viewModel = (TViewModel)scope.CreateInstance(typeof(TViewModel));
                   viewModelDisposer.Set(viewModel);
                 } else if(viewControlAsView.DataContext == null) { // View has no view model
-              viewModel = (TViewModel)CreateInstance(typeof(TViewModel));
+                  viewModel = (TViewModel)scope.CreateInstance(typeof(TViewModel));
                   viewModelDisposer.Set(viewModel);
                   viewControlAsView.DataContext = viewModel;
                 } else { // There's an existing view model
                   viewModel = viewControlAsView.DataContext as TViewModel;
                   if(viewModel == null) { // The existing view model is another type
-                viewModel = (TViewModel)CreateInstance(typeof(TViewModel));
+                    viewModel = (TViewModel)scope.CreateInstance(typeof(TViewModel));
                     viewModelDisposer.Set(viewModel);
                     viewControlAsView.DataContext = viewModel;
                   }
@@ -230,9 +266,14 @@ namespace Nuclex.Windows.Forms {
             }
 
             viewDisposer.Dismiss(); // Everything went well, we keep the view
-
           }
 
+          scopeDisposer.Dismiss(); // Everything went well, we keep the scope
+        }
+
+        setupScopeDisposal(viewControl, scope);
+      } // beauty scope
+
       return viewControl;
     }
 
@@ -322,8 +363,18 @@ namespace Nuclex.Windows.Forms {
       return Activator.CreateInstance(type);
     }
 
-    protected virtual object CreateServiceScope() {
-      return null;
+    /// <summary>Creates an instance of the specified type in a new scope</summary>
+    /// <param name="type">Type an instance will be created of</param>
+    /// <returns>The created instance and the scope in which it lives</returns>
+    /// <remarks>
+    ///   This is identical to <see cref="CreateInstance" /> but, if used together
+    ///   with a dependency injector, should also create a service scope. This way,
+    ///   an implicit service scope will cover the lifetime of a view model and
+    ///   any non-singleton services will use new instances, avoiding, for example,
+    ///   that multiple dialogs access the same database connection simultaneously.
+    /// </remarks>
+    protected virtual IWindowScope CreateWindowScope() {
+      return this.windowManagerAsScope;
     }
 
     /// <summary>Called when one of the application's root windows is closed</summary>
@@ -338,6 +389,7 @@ namespace Nuclex.Windows.Forms {
         ActiveWindow = null;
       }
 
+      // Application.Run() already does this and it's the user's responsibility anyways
       //disposeIfDisposable(closedWindow);
     }
 
@@ -392,7 +444,7 @@ namespace Nuclex.Windows.Forms {
     /// <param name="control">
     ///   Control whose view model will be disposed when it is itself disposed
     /// </param>
-    private void setupViewModelDisposal(Control control) {
+    private static void setupViewModelDisposal(Control control) {
       IView controlAsView = control as IView;
       if(controlAsView != null) {
         IDisposable disposableViewModel = controlAsView.DataContext as IDisposable;
@@ -408,6 +460,21 @@ namespace Nuclex.Windows.Forms {
       //window.SetValue(DisposeViewModelOnCloseProperty, true);
     }
 
+    /// <summary>Attaches a scope disposer to a control</summary>
+    /// <param name="control">
+    ///   Control that will dispose a scope when it is itself disposed
+    /// </param>
+    private void setupScopeDisposal(Control control, IWindowScope scope) {
+      if(!ReferenceEquals(scope, this.windowManagerAsScope)) {
+        IDisposable disposableScope = scope as IDisposable;
+        if(disposableScope != null) {
+          control.Disposed += delegate(object sender, EventArgs arguments) {
+            disposableScope.Dispose();
+          };
+        }
+      }
+    }
+
     /// <summary>Filters a list of types to contain only those in a specific namespace</summary>
     /// <param name="exportedTypes">List of exported types that will be filtered</param>
     /// <param name="filteredNamespace">
@@ -432,6 +499,8 @@ namespace Nuclex.Windows.Forms {
     private EventHandler rootWindowActivatedDelegate;
     /// <summary>Invoked when a root window has been closed</summary>
     private EventHandler rootWindowClosedDelegate;
+    /// <summary>Scope that uses the WindowManager's global CreateInstance() method</summary>
+    private WindowManagerScope windowManagerAsScope;
     /// <summary>View model binder that will be used on all created views</summary>
     private IAutoBinder autoBinder;
     /// <summary>Caches the view types to use for a view model</summary>