VCL类学习之(六) TCollectionItem

TCollectionItem represents an item in a collection.

Unit

Classes

Description

A TCollection holds a group of TCollectionItem objects. TCollectionItems are created and destroyed by TCollection抯 Add and Clear methods. Each TCollectionItem has a Collection property that points to the TCollection object to which the item belongs.

Objects descended from TCollection can contain objects descended from TCollectionItem. For example, a TDBGridColumns object contains TColumn objects; these two classes are used by TDBGrid to represent grid columns.

1.  TCollectionItem = class(TPersistent)
2.   private
3.     FCollection: TCollection;
4.     FID: Integer;
5.     function GetIndex: Integer;
6.   protected
7.     procedure Changed(AllItems: Boolean);
8.     function GetOwner: TPersistent; override;
9.     function GetDisplayName: string; virtual;
10.     procedure SetCollection(Value: TCollection); virtual;
11.     procedure SetIndex(Value: Integer); virtual;
12.     procedure SetDisplayName(const Value: string); virtual;
13.   public
14.     constructor Create(Collection: TCollection); virtual;
15.     destructor Destroy; override;
16.     function GetNamePath: string; override;
17.     property Collection: TCollection read FCollection write SetCollection;
18.     property ID: Integer read FID;
19.     property Index: Integer read GetIndex write SetIndex;
20.     property DisplayName: string read GetDisplayName write SetDisplayName;
21.   end;
23. { TCollectionItem }
25. constructor TCollectionItem.Create(Collection: TCollection);
26. begin
27.   SetCollection(Collection);
28. end;
30. destructor TCollectionItem.Destroy;
31. begin
32.   SetCollection(nil);
33.   inherited Destroy;
34. end;
36. procedure TCollectionItem.Changed(AllItems: Boolean);
37. var
38.   Item: TCollectionItem;
39. begin
40.   if (FCollection <> nil) and (FCollection.FUpdateCount = 0) then
41.   begin
42.     if AllItems then Item := nil else Item := Self;
43.     FCollection.Update(Item);
44.   end;
45. end;
47. function TCollectionItem.GetIndex: Integer;
48. begin
49.   if FCollection <> nil then
50.     Result := FCollection.FItems.IndexOf(Self) else
51.     Result := -1;
52. end;
54. function TCollectionItem.GetDisplayName: string;
55. begin
56.   Result := ClassName;
57. end;
59. function TCollectionItem.GetNamePath: string;
60. begin
61.   if FCollection <> nil then
62.     Result := Format('%s[%d]',[FCollection.GetNamePath, Index])
63.   else
64.     Result := ClassName;
65. end;
67. function TCollectionItem.GetOwner: TPersistent;
68. begin
69.   Result := FCollection;
70. end;
72. procedure TCollectionItem.SetCollection(Value: TCollection);
73. begin
74.   if FCollection <> Value then
75.   begin
76.     if FCollection <> nil then FCollection.RemoveItem(Self);
77.     if Value <> nil then Value.InsertItem(Self);
78.   end;
79. end;
81. procedure TCollectionItem.SetDisplayName(const Value: string);
82. begin
83.   Changed(False);
84. end;
86. procedure TCollectionItem.SetIndex(Value: Integer);
87. var
88.   CurIndex: Integer;
89. begin
90.   CurIndex := GetIndex;
91.   if (CurIndex >= 0) and (CurIndex <> Value) then
92.   begin
93.     FCollection.FItems.Move(CurIndex, Value);
94.     Changed(True);
95.   end;
96. end;