把一個”結構體”當做屬性後碰到的問題

當我把一個"結構體"在類中當做屬性後, 在實用中可以直接讀取結構體成員, 但不能直接寫入...

下面是由此引發的小練習:

unit Unit1;interfaceuses  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;type  TForm1 = class(TForm)    Button1: TButton;    Button2: TButton;    Button3: TButton;    Button4: TButton;    Button5: TButton;    procedure Button1Click(Sender: TObject);    procedure Button2Click(Sender: TObject);    procedure Button4Click(Sender: TObject);    procedure Button3Click(Sender: TObject);    procedure Button5Click(Sender: TObject);  end;  TMyClass = class  strict private    FPos: TPoint;    procedure SetPos(const Value: TPoint);  public    property Pos: TPoint read FPos write SetPos; //屬性 Pos 對應一個點結構  end;var  Form1: TForm1;implementation{$R *.dfm}{ TMyClass }procedure TMyClass.SetPos(const Value: TPoint);begin  FPos := Value;end;{測試}procedure TForm1.Button1Click(Sender: TObject);var  obj: TMyClass;begin  obj := TMyClass.Create;  ShowMessageFmt('%d, %d', [obj.Pos.X, obj.Pos.Y]); //可以直接存取結構中的元素//  obj.Pos.X := 11;  //但不能直接給結構中的元素賦值//  obj.Pos.Y := 22;  obj.Free;end;//變通一procedure TForm1.Button2Click(Sender: TObject);var  obj: TMyClass;begin  obj := TMyClass.Create;  obj.Pos := Point(22,33); //  ShowMessageFmt('%d, %d', [obj.Pos.X, obj.Pos.Y]);  obj.Free;end;//變通二procedure TForm1.Button3Click(Sender: TObject);var  obj: TMyClass;  pt: TPoint;begin  obj := TMyClass.Create;  pt.X := 33;  pt.Y := 44;  obj.Pos := pt;  ShowMessageFmt('%d, %d', [obj.Pos.X, obj.Pos.Y]);  obj.Free;end;//變通三(假如屬性的 get 不是方法)procedure TForm1.Button4Click(Sender: TObject);var  obj: TMyClass;  p: PPoint;begin  obj := TMyClass.Create;  p := Addr(obj.Pos);  p.X := 44;  p.Y := 55;  ShowMessageFmt('%d, %d', [obj.Pos.X, obj.Pos.Y]);  obj.Free;end;//變通四(假如屬性的 get 不是方法)procedure TForm1.Button5Click(Sender: TObject);var  obj: TMyClass;begin  obj := TMyClass.Create;  PPoint(Addr(obj.Pos)).X := 55;  PPoint(Addr(obj.Pos)).Y := 66;  ShowMessageFmt('%d, %d', [obj.Pos.X, obj.Pos.Y]);  obj.Free;end;end.

練習二:

unit Unit1;interfaceuses  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,  Vcl.Controls, Vcl.Forms, Vcl.Dialogs;type  TForm1 = class(TForm)    procedure FormCreate(Sender: TObject);  end;  TMyClass = class  private    FPos: TPoint;    function GetPos: TPoint;    procedure SetPos(const Value: TPoint);    function GetXY(const Index: Integer): Integer;    procedure SetXY(const Index, Value: Integer);  public    property Pos: TPoint read GetPos write SetPos;    property X: Integer index 0 read GetXY write SetXY;    property Y: Integer index 1 read GetXY write SetXY;  end;var  Form1: TForm1;implementation{$R *.dfm}{ TMyClass }function TMyClass.GetPos: TPoint;begin  Result := FPos;end;procedure TMyClass.SetPos(const Value: TPoint);begin  FPos := Value;end;function TMyClass.GetXY(const Index: Integer): Integer;begin  Result := 0;  case Index of    0: Result := FPos.X;    1: Result := FPos.Y;  end;end;procedure TMyClass.SetXY(const Index, Value: Integer);begin  case Index of    0: FPos.X := Value;    1: FPos.Y := Value;  end;end;{測試}procedure TForm1.FormCreate(Sender: TObject);var  obj: TMyClass;begin  obj := TMyClass.Create;  obj.X := 11;  obj.Y := 22;  ShowMessageFmt('%d, %d', [obj.Pos.X, obj.Pos.Y]);  obj.Free;end;end.