delphi - 如何调用给定实例的构造函数？

Question

我的第一个对象是 TGoodFairy (TObject)，它有自己的子对象 FChildren (TList)。有一个Assign过程，它复制任何TGoodFairy及其子项。

第二个对象是TBadFairy，它是TGoodFairy 的后代。

我正在努力如何使用 TBadFairy 的分配方法来创建 TBadFairy 子项。我想将 ClassType 与 Create 结合使用，以便为 TBadFairy 创建正确的子级(目前仅创建 TGoodFairy 子级)

  TGoodFairy = class (TObject)
  private
    FChildren:TList;
    FName:string;
  public
    constructor Create;
    destructor Destroy; override;
    procedure Assign(Source:TGoodFairy);
  published
    property Name:string read FName write FName;
  end;

  TBadFairy = class (TGoodFairy)
    procedure Assign(Source:TBadFairy);
  end;

------------------------

constructor TGoodFairy.Create;
begin
inherited;
FChildren:=TList.Create;
end;

destructor TGoodFairy.Destroy;
var i:integer;
begin
for i:=0 to FChildren.Count-1 do TGoodFairy(FChildren[i]).Free;
FChildren.Clear;
FChildren.Free;
inherited;
end;

procedure TGoodFairy.Assign(Source:TGoodFairy);
var i:integer;
    f:TGoodFairy;
    C:TClass;
begin
    FName:=Source.Name;
    for i:=0 to Source.FChildren.Count-1 do
    begin
    //C := Source.ClassType;
    //f := C.Create; 
    f := TGoodFairy.Create;  //<-- this should be parametrized somehow
    f.Assign(Source.FChildren[i]);
    FChildren.Add(f);
    end;
end;


procedure TBadFairy.Assign(Source:TBadFairy);
begin
inherited Assign(Source);
end;

Answer 1

尝试更多类似这样的事情:

type
  TFairy = class(TObject)
  private
    FChildren: TObjectList;
    FName: string;
  public
    constructor Create; virtual;
    destructor Destroy; override;
    procedure Assign(Source: TFairy); virtual;
  published
    property Name: string read FName write FName;
  end;

  TFairyClass = class of TFairy;

  TGoodFairy = class(TFairy)
  end;

  TBadFairy = class(TFairy)
  end;

constructor TFairy.Create;
begin
  inherited;
  FChildren := TObjectList.Create(True);
end;

destructor TFairy.Destroy;
begin
  FChildren.Free;
  inherited;
end;

procedure TFairy.Assign(Source: TFairy);
var
  i: integer;
  f, child: TFairy;
begin
  FName := Source.Name;
  FChildren.Clear;
  for i := 0 to Source.FChildren.Count-1 do
  begin
    child := TFairy(Source.FChildren[i]);
    f := TFairyClass(child.ClassType).Create;
    try
      f.Assign(child);
      FChildren.Add(f);
    except
      f.Free;
      raise;
    end;
  end;
end;