delphi – 从调用重写过程的公共类类型继承的对象列表？

我正在构建一个自定义OpenGL控件,它包含一个项目列表,其中每个项目可能是不同的类,但继承自某个公共类类型.我不知道如何以这样的方式执行此操作,即我可以循环执行这些项并执行某些操作,这些操作有望在继承的类中被覆盖.

更具体地说,这是一个视觉对象列表,用于绘制画布.我有一个公共类TGLItem,用于创建许多继承类.例如,TGLCar继承自TGLItem并被添加到列表TGLItems中.此自定义列表类是控件的一部分.

当控件绘制时,它会遍历此项目列表并调用每个项目的Draw过程. Draw旨在被实现项目实际绘制的继承类覆盖.所以真正的工作是从Draw程序完成的,它在TGLCar类中实现,但它只从主控件调用.

主控件(TGLImage)不知道实际的继承项是什么,但能够调用其Draw过程,期望它绘制到OpenGL.

如何以适应此方案的方式构建此项目列表和项目库？这是我到目前为止所拥有的：

TGLItems = class(TPersistent)
  private
    FItems: TList;
    function GetItem(Index: Integer): TGLItem;
    procedure SetItem(Index: Integer; const Value: TGLItem);
  public
    constructor Create;
    destructor Destroy; override;
    procedure Add(AItem: TGLItem);
    function Count: Integer;
    property Items[Index: Integer]: TGLItem read GetItem write SetItem; default;
  end;

  TGLItem = class(TPersistent)
  private
    FPosition: TGLPosition;
    FDimensions: TGLDimensions;
    FOwner: TGLItems;
    FItemClass: TGLItemClass;
    procedure PositionChanged(Sender: TObject);
    procedure DimensionsChanged(Sender: TObject);
    procedure SetPosition(const Value: TGLPosition);
    procedure SetDimensions(const Value: TGLDimensions);
  public
    constructor Create(Owner: TGLItems);
    destructor Destroy; override;
    procedure Draw;
    property Owner: TGLItems read FOwner;
    property ItemClass: TGLItemClass read FItemClass;
  published
    property Position: TGLPosition read FPosition write SetPosition;
    property Dimensions: TGLDimensions read FDimensions write SetDimensions;
  end;

实现…

{ TGLItem }

constructor TGLItem.Create;
begin
  FPosition:= TGLPosition.Create;
  FPosition.OnChange:= PositionChanged;
  FDimensions:= TGLDimensions.Create;
  FDimensions.OnChange:= DimensionsChanged;
end;

destructor TGLItem.Destroy;
begin
  FPosition.Free;
  FDimensions.Free;
  inherited;
end;

procedure TGLItem.DimensionsChanged(Sender: TObject);
begin

end;

procedure TGLItem.Draw;
begin
  //Draw to gl scene

end;

procedure TGLItem.PositionChanged(Sender: TObject);
begin

end;

procedure TGLItem.SetDimensions(const Value: TGLDimensions);
begin
  FDimensions.Assign(Value);
end;

procedure TGLItem.SetPosition(const Value: TGLPosition);
begin
  FPosition.Assign(Value);
end;

{ TGLItems }

procedure TGLItems.Add(AItem: TGLItem);
begin
  FItems.Add(AItem);
  //Expects objects to be created and maintained elsewhere
  //This list object will not create/destroy any items
end;

function TGLItems.Count: Integer;
begin
  Result:= FItems.Count;
end;

constructor TGLItems.Create;
begin
  FItems:= TList.Create;
end;

destructor TGLItems.Destroy;
begin
  FItems.Free;
  inherited;
end;

function TGLItems.GetItem(Index: Integer): TGLItem;
begin
  Result:= TGLItem(FItems[Index]);
end;

procedure TGLItems.SetItem(Index: Integer; const Value: TGLItem);
begin
  TGLItem(FItems[Index]).Assign(Value);
end;

OpenGL的一部分并不一定与这种情况相关,我只是想解释一下这个目的的一些细节,以便了解我希望如何工作.

我还想到将TGLItems列表对象传递给其构造函数中的每个单独项目,并让每个项目在项目列表中注册其自身.在这种情况下,项目列表将没有任何添加过程,我可能甚至不需要单独的列表对象.我确信应该有一些重要的技巧,我错过了,我愿意对结构进行任何大规模的更改,以便更有效地适应这种情况.

program Project1;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  SysUtils;  // XE2: uses System.SysUtils;

type
  TBase = class(TObject)
    procedure Draw(const Msg: string); virtual; abstract;
  end;

  TChildOne = class(TBase)
    procedure Draw(const Msg: string); override;
  end;

  TChildTwo = class(TBase)
    procedure Draw(const Msg: string); override;
  end;

  TBaseArray = array of TBase;

procedure TChildOne.Draw(const Msg: string);
begin
  // Hard-coded for clarity. Change to something like this
  // to see without hard-coded name
  // WriteLn(Self.ClassName + '.Draw: ',Msg);
  Writeln('Type TChildOne.Draw: ',Msg);
end;

procedure TChildTwo.Draw(const Msg: string);
begin
  // Note missing 'T' before class type to make more apparent.
  // See note in TChildOne.Draw about removing hard-coded classname
  WriteLn('Type ChildTwo.Draw: ',Msg);
end;

var
  BaseArray: TBaseArray;
  i: Integer;

const
  NumChildren = 10;

begin
  SetLength(BaseArray,NumChildren);

  for i := 0 to NumChildren - 1 do
  begin
    if Odd(i) then
      BaseArray[i] := TChildOne.Create
    else
      BaseArray[i] := TChildTwo.Create;
  end;

  for i := NumChildren - 1 downto 0 do
    BaseArray[i].Draw('This is index ' + IntToStr(i));
  Readln;

end.