當我把一個"結構體"在類中當做屬性后, 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:

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unit Unit1;interfaceusesWinapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;typeTForm1 = 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 = classstrict privateFPos: TPoint;procedure SetPos(const Value: TPoint);publicproperty Pos: TPoint read FPos write SetPos; //屬性 Pos 對應一個點結構end;varForm1: TForm1;implementation{$R *.dfm}{ TMyClass }procedure TMyClass.SetPos(const Value: TPoint); beginFPos := Value; end;{測試}procedure TForm1.Button1Click(Sender: TObject); varobj: TMyClass; beginobj := TMyClass.Create;ShowMessageFmt('%d, %d', [obj.Pos.X, obj.Pos.Y]); //可以直接訪問結構中的元素 // 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); varobj: TMyClass; beginobj := 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); varobj: TMyClass;pt: TPoint; beginobj := 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); varobj: TMyClass;p: PPoint; beginobj := 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); varobj: TMyClass; beginobj := 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.

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練習二:

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unit Unit1;interfaceusesWinapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,Vcl.Controls, Vcl.Forms, Vcl.Dialogs;typeTForm1 = class(TForm)procedure FormCreate(Sender: TObject);end;TMyClass = classprivateFPos: TPoint;function GetPos: TPoint;procedure SetPos(const Value: TPoint);function GetXY(const Index: Integer): Integer;procedure SetXY(const Index, Value: Integer);publicproperty 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;varForm1: TForm1;implementation{$R *.dfm}{ TMyClass }function TMyClass.GetPos: TPoint; beginResult := FPos; end;procedure TMyClass.SetPos(const Value: TPoint); beginFPos := Value; end;function TMyClass.GetXY(const Index: Integer): Integer; beginResult := 0;case Index of0: Result := FPos.X;1: Result := FPos.Y;end; end;procedure TMyClass.SetXY(const Index, Value: Integer); begincase Index of0: FPos.X := Value;1: FPos.Y := Value;end; end;{測試} procedure TForm1.FormCreate(Sender: TObject); varobj: TMyClass; beginobj := TMyClass.Create;obj.X := 11;obj.Y := 22;ShowMessageFmt('%d, %d', [obj.Pos.X, obj.Pos.Y]);obj.Free; end;end.

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總結

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