集合编辑器不会为TPersistent属性中的TCollection属性打开

Question

我有自定义集合属性,当它是我的组件的直接成员时,它工作得很好.

但我想将集合属性移动到我的组件中的TPersistent属性.现在出现问题,它不起作用:双击对象检查器中的集合属性通常会打开集合编辑器,但它不再存在.

所有的拳头 - 我应该传递给TPersistent属性的构造函数？

TMyCollection = class(TCollection)
  constructor Create(AOwner: TComponent); // TMyCollection constuctor
  ...

我无法通过自我,所以我应该通过我的执着主人？

constructor TMyPersistent.Create(AOwner: TComponent);
begin
  inherited Create;
  fOwner := AOwner;
  fMyCollection := TMyCollection.Create(AOwner); // hmmm... doesn't make sense
end;

我想我错过了什么.如果需要更多代码,请评论此帖.

Answer 1

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,对构造函数没有任何影响.

更新

不同之处在于所有权,但在TPersistent级别,应该通过正确的实施来管理GetOwner:

GetOwner返回对象的所有者.GetName方法使用GetOwner来查找持久对象的所有者.在TPersistent中引入了GetNamePath和GetOwner,因此集合等后代可以出现在Object Inspector中.

您必须告诉IDE您的TCollection属性归TPersistent属性所有,而TPersistent属性又由组件拥有.

您正在使用的教程有关此实现的几个错误:

• 集合的所有者声明为TComponent,应该是TPersistent,
• GetOwner未针对TPersistent属性类实现,并且
• 本教程末尾显示的修复,指出TPersistent属性应该继承TComponent,这是完全错误的; 或者更好地说:相对于没有实现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TOwnedCollection,这使得TMyCollection的使用和声明变得更加简单:

  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;