The progress spinner can now tell its optimal size required to show the entire status text but overlap as few controls as possible; began implementing a generic version of a multi page view model and matching view with caching

git-svn-id: file:///srv/devel/repo-conversion/nuwi@53 d2e56fa2-650e-0410-a79f-9358c0239efd

Source/ViewModels/IMultiPageViewModel.cs

@@ -0,0 +1,14 @@
+using System;
+
+namespace Nuclex.Windows.Forms.ViewModels {
+
+  /// <summary>Interface for vew models that can switch between different pages</summary>
+  public interface IMultiPageViewModel {
+
+    /// <summary>Retrieves (and, if needed, creates) the view model for the active page</summary>
+    /// <returns>A view model for the active page on the multi-page view model</returns>
+    object GetActivePageViewModel();
+
+  }
+
+} // namespace Nuclex.Windows.Forms.ViewModels

Source/ViewModels/MultiPageViewModel.cs

@@ -19,6 +19,7 @@ License along with this library
 #endregion
 
 using System;
+using System.Collections.Concurrent;
 
 using Nuclex.Support;
 
@@ -26,8 +27,8 @@ namespace Nuclex.Windows.Forms.ViewModels {
 
   /// <summary>Base class for view models that have multiple child view models</summary>
   /// <typeparam name="TPageEnumeration">Enum type by which pages can be indicated</typeparam>
-  public abstract class MultiPageViewModel<TPageEnumeration> : Observable
-    where TPageEnumeration : IEquatable<TPageEnumeration> {
+  public abstract class MultiPageViewModel<TPageEnumeration> :
+    Observable, IMultiPageViewModel, IDisposable { 
 
     /// <summary>Initializes a new multi-page view model</summary>
     /// <param name="windowManager">
@@ -38,6 +39,25 @@ namespace Nuclex.Windows.Forms.ViewModels {
     /// </param>
     public MultiPageViewModel(IWindowManager windowManager, bool cachePageViewModels = false) {
       this.windowManager = windowManager;
+      if(cachePageViewModels) {
+        this.cachedViewModels = new ConcurrentDictionary<TPageEnumeration, object>();
+      }
+    }
+
+    /// <summary>Immediately releases all resources owned by the instance</summary>
+    public virtual void Dispose() {
+      if(this.cachedViewModels != null) {
+        foreach(object cacheViewModel in this.cachedViewModels.Values) {
+          disposeIfSupported(cacheViewModel);
+        }
+        this.activePageViewModel = null;
+
+        this.cachedViewModels.Clear();
+        this.cachedViewModels = null;
+      } else if(this.activePageViewModel != null) {
+        disposeIfSupported(this.activePageViewModel);
+        this.activePageViewModel = null;
+      }
     }
 
     /// <summary>Child page that is currently being displayed by the view model</summary>
@@ -46,11 +66,36 @@ namespace Nuclex.Windows.Forms.ViewModels {
       set {
         if(!this.activePage.Equals(value)) {
           this.activePage = value;
+          if(this.activePageViewModel != null) {
+            if(this.cachedViewModels == null) {
+              disposeIfSupported(this.activePageViewModel);
+            }
+            this.activePageViewModel = null;
+          }
           OnPropertyChanged(nameof(ActivePage));
         }
       }
     }
 
+    /// <summary>Retrieves (and, if needed, creates) the view model for the active page</summary>
+    /// <returns>A view model for the active page on the multi-page view model</returns>
+    public object GetActivePageViewModel() {
+      if(this.cachedViewModels == null) {
+        if(this.activePageViewModel == null) {
+          this.activePageViewModel = CreateViewModelForPage(this.activePage);
+        }
+      } else if(this.activePageViewModel == null) {
+        this.activePageViewModel = this.cachedViewModels.GetOrAdd(
+          this.activePage,
+          delegate(TPageEnumeration activePage) {
+            return CreateViewModelForPage(this.activePage);
+          }
+        );
+      }
+
+      return this.activePageViewModel;
+    }
+
     /// <summary>Windowmanager that can create view models and display other views</summary>
     protected IWindowManager WindowManager {
       get { return this.windowManager; }
@@ -59,13 +104,27 @@ namespace Nuclex.Windows.Forms.ViewModels {
     /// <summary>Creates a view model for the specified page</summary>
     /// <param name="page">Page for which a view model will be created</param>
     /// <returns>The view model for the specified page</returns>
-    protected abstract object createViewModelForPage(TPageEnumeration page);
+    protected abstract object CreateViewModelForPage(TPageEnumeration page);
+
+    /// <summary>Disposes the specified object if it is disposable</summary>
+    /// <param name="potentiallyDisposable">Object that will be disposed if supported</param>
+    private static void disposeIfSupported(object potentiallyDisposable) {
+      var disposable = potentiallyDisposable as IDisposable;
+      if(disposable != null) {
+        disposable.Dispose();
+      }
+    }
 
     /// <summary>Page that is currently active in the multi-page view model</summary>
     private TPageEnumeration activePage;
     /// <summary>Window manager that can be used to display other views</summary>
     private IWindowManager windowManager;
 
+    /// <summary>View model for the active page</summary>
+    private object activePageViewModel;
+    /// <summary>Cached page view models, if caching is enabled</summary>
+    private ConcurrentDictionary<TPageEnumeration, object> cachedViewModels;
+
   }
 
 } // namespace Nuclex.Windows.Forms.ViewModels