TCollection 的构造函数不需要 TComponent,而是 TCollectionItemClass。
您的集合现在是 TPersistent 属性的成员,而不是组件的直接成员,这对构造函数没有任何影响。
更新
不同的是所有权,但是在 TPersistent 级别,应该通过正确的实现来管理GetOwner
:
GetOwner 返回对象的所有者。GetNamePath 方法使用 GetOwner 来查找持久对象的所有者。TPersistent 中引入了 GetNamePath 和 GetOwner,因此集合之类的后代可以出现在 Object Inspector 中。
您必须告诉 IDE 您的 TCollection 属性归 TPersistent 属性所有,而 TPersistent 属性又归组件所有。
您正在使用的教程有几个关于此实现的错误:
- 集合的所有者声明为TComponent,应该是TPersistent,
- TPersistent 属性类没有实现 GetOwner,并且
- 教程末尾显示的修复说明 TPersistent 属性应该从 TComponent 继承,这是完全错误的;或者说得更好:是一种不实现 GetOwner 的解决方法。
它应该是这样的:
unit MyComponent;
interface
uses
Classes, SysUtils;
type
TMyCollectionItem = class(TCollectionItem)
private
FStringProp: String;
protected
function GetDisplayName: String; override;
public
procedure Assign(Source: TPersistent); override;
published
property StringProp: String read FStringProp write FStringProp;
end;
TMyCollection = class(TCollection)
private
FOwner: TPersistent;
function GetItem(Index: Integer): TMyCollectionItem;
procedure SetItem(Index: Integer; Value: TMyCollectionItem);
protected
function GetOwner: TPersistent; override;
public
constructor Create(AOwner: TPersistent);
function Add: TMyCollectionItem;
function Insert(Index: Integer): TMyCollectionItem;
property Items[Index: Integer]: TMyCollectionItem read GetItem
write SetItem;
end;
TMyPersistent = class(TPersistent)
private
FOwner: TPersistent;
FCollectionProp: TMyCollection;
procedure SetCollectionProp(Value: TMyCollection);
protected
function GetOwner: TPersistent; override;
public
procedure Assign(Source: TPersistent); override;
constructor Create(AOwner: TPersistent);
destructor Destroy; override;
published
property CollectionProp: TMyCollection read FCollectionProp
write SetCollectionProp;
end;
TMyComponent = class(TComponent)
private
FPersistentProp: TMyPersistent;
procedure SetPersistentProp(Value: TMyPersistent);
public
constructor Create(AOwner: TComponent); override;
destructor Destroy; override;
published
property PersistentProp: TMyPersistent read FPersistentProp
write SetPersistentProp;
end;
procedure Register;
implementation
procedure Register;
begin
RegisterComponents('Samples', [TMyComponent]);
end;
{ TMyCollectionItem }
procedure TMyCollectionItem.Assign(Source: TPersistent);
begin
if Source is TMyCollectionItem then
FStringProp := TMyCollectionItem(Source).FStringProp
else
inherited Assign(Source);
end;
function TMyCollectionItem.GetDisplayName: String;
begin
Result := Format('Item %d',[Index]);
end;
{ TMyCollection }
function TMyCollection.Add: TMyCollectionItem;
begin
Result := TMyCollectionItem(inherited Add);
end;
constructor TMyCollection.Create(AOwner: TPersistent);
begin
inherited Create(TMyCollectionItem);
FOwner := AOwner;
end;
function TMyCollection.GetItem(Index: Integer): TMyCollectionItem;
begin
Result := TMyCollectionItem(inherited GetItem(Index));
end;
function TMyCollection.GetOwner: TPersistent;
begin
Result := FOwner;
end;
function TMyCollection.Insert(Index: Integer): TMyCollectionItem;
begin
Result := TMyCollectionItem(inherited Insert(Index));
end;
procedure TMyCollection.SetItem(Index: Integer; Value: TMyCollectionItem);
begin
inherited SetItem(Index, Value);
end;
{ TMyPersistent }
procedure TMyPersistent.Assign(Source: TPersistent);
begin
if Source is TMyPersistent then
CollectionProp := TMyPersistent(Source).FCollectionProp
else
inherited Assign(Source);
end;
constructor TMyPersistent.Create(AOwner: TPersistent);
begin
inherited Create;
FOwner := AOwner;
FCollectionProp := TMyCollection.Create(Self);
end;
destructor TMyPersistent.Destroy;
begin
FCollectionProp.Free;
inherited Destroy;
end;
function TMyPersistent.GetOwner: TPersistent;
begin
Result := FOwner;
end;
procedure TMyPersistent.SetCollectionProp(Value: TMyCollection);
begin
FCollectionProp.Assign(Value);
end;
{ TMyComponent }
constructor TMyComponent.Create(AOwner: TComponent);
begin
inherited Create(AOwner);
FPersistentProp := TMyPersistent.Create(Self);
end;
destructor TMyComponent.Destroy;
begin
FPersistentProp.Free;
inherited Destroy;
end;
procedure TMyComponent.SetPersistentProp(Value: TMyPersistent);
begin
FPersistentProp.Assign(Value);
end;
end.
但是我可以说你也可以继承 from TOwnedCollection
,这使得 TMyCollection 的使用和声明更加简单:
TMyCollection = class(TOwnedCollection)
private
function GetItem(Index: Integer): TMyCollectionItem;
procedure SetItem(Index: Integer; Value: TMyCollectionItem);
public
function Add: TMyCollectionItem;
function Insert(Index: Integer): TMyCollectionItem;
property Items[Index: Integer]: TMyCollectionItem read GetItem
write SetItem;
end;