scrollbox直接增加casvas功能

如果你要保持一個ScrollBox的VCL物件的話, 可以開一個新的MyCanvas.
然後利用MyCanvas.Control指向ScollBox, 那麼你的ScrollBox就擁有Canvas的功能。如果你可以用run time才去Create ScollBox的話, 大可Create一個新的Type繼承ScrollBox, 然後新增一個Property, 而MyCanvas.Control:=Self;即可。

type
    TForm1 = class(TForm)
    ScrollBox1: TScrollBox;
    Button1: TButton;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    private
    FMyCanvas: TControlCanvas;
    procedure SetMyCanvas(const Value: TControlCanvas);
    { Private declarations }
    public
    { Public declarations }
    property MyCanvas: TControlCanvas read FMyCanvas write SetMyCanvas; // 開一個新的自訂屬性..
    end;

var
    Form1: TForm1;

implementation

{$R *.dfm}

{ TForm1 }

procedure TForm1.SetMyCanvas(const Value: TControlCanvas);
begin
    FMyCanvas := Value;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
    FMyCanvas:=TControlCanvas.Create;
    FMyCanvas.Control:=ScrollBox1; // 把Canvas與ScrollBox連結;
end;

// 這一段是試看看有沒有畫出來..
procedure TForm1.Button1Click(Sender: TObject);
begin
    MyCanvas.Pen.Color:=clRed;
    MyCanvas.MoveTo(0,0);
    MyCanvas.LineTo(100,100);
end;