Manage IViews references in a list

Implements a list of IView instances that are referenced by tree nodes.

This list is necessary to maintain IView reference counts since the
tree nodes only maintain weak references via pointers.

Original commit by @SirRufo per PR#160 modified only by adding /
updating comments.

Author: delphidabbler

Src/FrOverview.pas

@@ -18,6 +18,7 @@ interface
 
 uses
   // Delphi
+  Generics.Collections,
   ComCtrls, Controls, Classes, Windows, ExtCtrls, StdCtrls, ToolWin, Menus,
   // Project
   DB.USnippet, FrTitled, IntfFrameMgrs, IntfNotifier, UCommandBars,
@@ -88,6 +89,8 @@       TTVDraw = class(TSnippetsTVDraw)
       end;
 
     var
+      fViewStore : TList<IView>;    // Stores references to IView instances that
+                                    // have weak references in tree nodes
       fTVDraw: TTVDraw;             // Object that renders tree view nodes
       fNotifier: INotifier;         // Notifies app of user initiated events
       fCanChange: Boolean;          // Whether selected node allowed to change
@@ -284,6 +287,7 @@ constructor TOverviewFrame.Create(AOwner: TComponent);
   TabIdx: Integer;  // loops through tabs
 begin
   inherited;
+  fViewStore := TList<IView>.Create;
   // Create delegated (contained) command bar manager for toolbar and popup menu
   fCommandBars := TCommandBarMgr.Create(Self);
   fCommandBars.AddCommandBar(
@@ -319,6 +323,7 @@ destructor TOverviewFrame.Destroy;
   fSelectedItem := nil;
   fSnippetList.Free;  // does not free referenced snippets
   fCommandBars.Free;
+  fViewStore.Free;
   inherited;
 end;
 
@@ -520,7 +525,7 @@ procedure TOverviewFrame.Redisplay;
       Exit;
     // Build new treeview using grouping determined by selected tab
     Builder := BuilderClasses[tcDisplayStyle.TabIndex].Create(
-      tvSnippets, fSnippetList
+      tvSnippets, fSnippetList, fViewStore
     );
     Builder.Build;
     // Restore state of treeview based on last time it was displayed

Src/UOverviewTreeBuilder.pas

@@ -18,6 +18,7 @@ interface
 
 uses
   // Delphu
+  Generics.Collections,
   ComCtrls,
   // Project
   DB.USnippet, UGroups, UView, UViewItemTreeNode;
@@ -32,13 +33,23 @@ interface
   TOverviewTreeBuilder = class abstract(TObject)
   strict private
     var
-      fTreeView: TTreeView;       // Value of TreeView property
-      fSnippetList: TSnippetList; // Value of SnippetList property
+      // Property values
+      fTreeView: TTreeView;
+      fSnippetList: TSnippetList;
+      fViewStore: TList<IView>;
   strict protected
     property TreeView: TTreeView read fTreeView;
       {Reference to treeview populated by class}
     property SnippetList: TSnippetList read fSnippetList;
       {List of snippets to be displayed in treeview}
+    ///  <summary>List of <c>IView</c> instances referenced by treeview nodes.
+    ///  </summary>
+    ///  <remarks>This list is required to maintain reference counting of
+    ///  <c>IView</c>s because the tree nodes only store weak references.
+    ///  </remarks>
+    property ViewStore : TList<IView> read fViewStore;
+      {List of IView instances referenced (weakly) by treeview nodes. This list
+      maintains maintains reference counting}
     function AddViewItemNode(const ParentNode: TViewItemTreeNode;
       ViewItem: IView): TViewItemTreeNode;
       {Adds a new node to the tree view that represents a view item.
@@ -57,12 +68,16 @@   TOverviewTreeBuilder = class abstract(TObject)
         @return Required view item object.
       }
   public
-    constructor Create(const TV: TTreeView; const SnippetList: TSnippetList);
-      {Class constructor. Sets up object to populate a treeview with a list of
-      snippets.
-        @param TV [in] Treeview control to be populated.
-        @param SnippetList [in] List of snippets to be added to TV.
-      }
+    ///  <summary>Constructs an object to populate a tree view with a list of
+    ///  snippets.</summary>
+    ///  <param name="TV"><c>TTreeView</c> [in] Treeview control to be
+    ///  populated.</param>
+    ///  <param name="SnippetList"><c>TSnippetList</c> [in] List of snippets to
+    ///  be added to the treeview.</param>
+    ///  <param name="ViewStore"><c>TList&lt;IView&gt;</c> [in] Receives a list
+    ///  of view items, one per tree node.</param>
+    constructor Create(const TV: TTreeView; const SnippetList: TSnippetList;
+      const ViewStore: TList<IView>);
     procedure Build;
       {Populates the treeview.
       }
@@ -177,7 +192,9 @@ procedure TOverviewTreeBuilder.Build;
   ParentNode: TViewItemTreeNode;  // each section node in tree
   Grouping: TGrouping;            // groups snippets
   Group: TGroupItem;              // each group of snippets
+  View: IView;
 begin
+  ViewStore.Clear;
   // Create required grouping of snippets
   Grouping := CreateGrouping;
   try
@@ -186,11 +203,17 @@ procedure TOverviewTreeBuilder.Build;
     begin
       if not Group.IsEmpty or Preferences.ShowEmptySections then
       begin
-        ParentNode := AddViewItemNode(nil, CreateViewItemForGroup(Group));
+        View := CreateViewItemForGroup(Group);
+        ParentNode := AddViewItemNode(nil, View);
+        ViewStore.Add(View);
         for Snippet in Group.SnippetList do
+        begin
+          View := TViewFactory.CreateSnippetView(Snippet);
           AddViewItemNode(
-            ParentNode, TViewFactory.CreateSnippetView(Snippet)
+            ParentNode, View
           );
+          ViewStore.Add(View);
+        end;
       end;
     end;
   finally
@@ -199,16 +222,12 @@ procedure TOverviewTreeBuilder.Build;
 end;
 
 constructor TOverviewTreeBuilder.Create(const TV: TTreeView;
-  const SnippetList: TSnippetList);
-  {Class constructor. Sets up object to populate a treeview with a list of
-  snippets.
-    @param TV [in] Treeview control to be populated.
-    @param SnippetList [in] List of snippets to be added to TV.
-  }
+  const SnippetList: TSnippetList; const ViewStore: TList<IView>);
 begin
   inherited Create;
   fTreeView := TV;
   fSnippetList := SnippetList;
+  fViewStore := ViewStore;
 end;
 
 { TOverviewCategorisedTreeBuilder }

Src/UViewItemTreeNode.pas

@@ -24,21 +24,33 @@ interface
 
 
 type
-  {
-  TViewItemTreeNode:
-    Custom tree node class that adds ability to store reference to a view item
-    in a tree node.
-  }
+  ///  <summary>Custom tree node class that adds a property to store a weak
+  ///  reference to an <c>IView</c> instance in a tree node.</summary>
   TViewItemTreeNode = class(TTreeNode)
   strict private
-    var fViewItem: IView; // Value of ViewItem property
+    function GetViewItem: IView;
+    procedure SetViewItem(const Value: IView);
   public
-    property ViewItem: IView read fViewItem write fViewItem;
-      {View item associated with tree node}
+    ///  <summary>View item associated with tree node.</summary>
+    ///  <remarks>NOTE: This view item is stored as a weak reference via a
+    ///  pointer so the reference count is not updated.</remarks>
+    property ViewItem: IView read GetViewItem write SetViewItem;
   end;
 
 
 implementation
 
+{ TViewItemTreeNode }
+
+function TViewItemTreeNode.GetViewItem: IView;
+begin
+  Result := IView(Data);
+end;
+
+procedure TViewItemTreeNode.SetViewItem(const Value: IView);
+begin
+  Data := Pointer(Value);
+end;
+
 end.