如何给Button加上Canvas?在线，解决就结贴，UP有分。

Question

从TButton继承一个新类，添加一个属性Canvas.在TButton.Create，里面创建TCanvas对象

Answer 1

就是给没有Canvas的控件加上Canvas的属性。
我看过一篇上面说在  published　加可是不管用。

Answer 2

我同意debussy(debussy)的
你可以自制一个控件
继承tbutton

Answer 3

to debussy(debussy)
to zhptj(北狼) 
我就是继承tbutton，可是要怎样写呀？

Answer 4

看我的：// 先放两个按钮unit Unit1;interfaceuses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    procedure Button2Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
    MyCanvas: TCanvas;
  end;var
  Form1: TForm1;implementation{$R *.dfm}procedure TForm1.Button2Click(Sender: TObject);
begin
  MyCanvas.Handle := GetDC(Button1.Handle);
  MyCanvas.Ellipse(2, 2, 8, 8);
end;procedure TForm1.FormCreate(Sender: TObject);
begin
  MyCanvas := TCanvas.Create;
end;procedure TForm1.FormDestroy(Sender: TObject);
begin
  MyCanvas.Free;
end;end.////////////////////////////////////////思想就是取得 Button 的 HDC ，传给 MyCanvas ......

Answer 5

看我的：// 先放两个按钮unit Unit1;interfaceuses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    procedure Button2Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
    MyCanvas: TCanvas;
  end;var
  Form1: TForm1;implementation{$R *.dfm}procedure TForm1.Button2Click(Sender: TObject);
begin
  MyCanvas.Handle := GetDC(Button1.Handle);
  MyCanvas.Ellipse(2, 2, 8, 8);
end;procedure TForm1.FormCreate(Sender: TObject);
begin
  MyCanvas := TCanvas.Create;
end;procedure TForm1.FormDestroy(Sender: TObject);
begin
  MyCanvas.Free;
end;end.////////////////////////////////////////思想就是取得 Button 的 HDC ，传给 MyCanvas ......

Answer 6

对原来没有Canvas的控件
要在private段定义
    FCanvas: TCanvas;不是在published，published中是从父类继承的属性。

Answer 7

那么如何在 TButton 类中引入 Canvas 呢，看看 TCustomControl :TCustomControl = class(TWinControl)
  private
    FCanvas: TCanvas;
    procedure WMPaint(var Message: TWMPaint); message WM_PAINT;
  protected
    procedure Paint; virtual;
    procedure PaintWindow(DC: HDC); override;
    property Canvas: TCanvas read FCanvas;
  public
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
  end;{ TCustomControl }constructor TCustomControl.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  FCanvas := TControlCanvas.Create;
  TControlCanvas(FCanvas).Control := Self;
end;destructor TCustomControl.Destroy;
begin
  FCanvas.Free;
  inherited Destroy;
end;procedure TCustomControl.WMPaint(var Message: TWMPaint);
begin
  Include(FControlState, csCustomPaint);
  inherited;
  Exclude(FControlState, csCustomPaint);
end;procedure TCustomControl.PaintWindow(DC: HDC);
begin
  FCanvas.Lock;
  try
    FCanvas.Handle := DC;
    try
      TControlCanvas(FCanvas).UpdateTextFlags;
      Paint;
    finally
      FCanvas.Handle := 0;
    end;
  finally
    FCanvas.Unlock;
  end;
end;procedure TCustomControl.Paint;
begin
end;

Answer 8

torble(阿裕) 的已经分析得很清楚，你只要参照写进去就行了，我没什么好说的了。

Answer 9

不行,出错，谁还能帮我看看？unit Button1;interfaceuses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;type
  TButton1 = class(TButton)
  private
    FCanvas: TCanvas;
    procedure WMPaint(var Message: TWMPaint); message WM_PAINT;
  protected
    procedure Paint; virtual;
    procedure PaintWindow(DC: HDC); override;
    property Canvas: TCanvas read FCanvas;
  public
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
  end;
procedure Register;implementationconstructor TButton1.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  FCanvas := TControlCanvas.Create;
  TControlCanvas(FCanvas).Control := Self;
end;destructor TButton1.Destroy;
begin
  FCanvas.Free;
  inherited Destroy;
end;procedure TButton1.WMPaint(var Message: TWMPaint);
begin
  Include(FControlState, csCustomPaint);
  inherited;
  Exclude(FControlState, csCustomPaint);
end;procedure TButton1.PaintWindow(DC: HDC);
begin
  FCanvas.Lock;
  try
    FCanvas.Handle := DC;
    try
      TControlCanvas(FCanvas).UpdateTextFlags;
      Paint;
    finally
      FCanvas.Handle := 0;
    end;
  finally
    FCanvas.Unlock;
  end;
end;procedure TButton1.Paint;
begin
end;procedure Register;
begin
  RegisterComponents('Samples', [TButton1]);
end;end.

Answer 10

unit Button1;interfaceuses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;type
  TButton1 = class(TButton)
  private
    FCanvas: TCanvas;
//加一句
    FControlState: TControlState; 
    procedure WMPaint(var Message: TWMPaint); message WM_PAINT;
  protected
    procedure Paint; virtual;
    procedure PaintWindow(DC: HDC); override;
//    property Canvas: TCanvas read FCanvas;
  public
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
    property Canvas: TCanvas read FCanvas;
  end;
procedure Register;implementationconstructor TButton1.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  FCanvas := TControlCanvas.Create;
  TControlCanvas(FCanvas).Control := Self;
end;destructor TButton1.Destroy;
begin
  FCanvas.Free;
  inherited Destroy;
end;procedure TButton1.WMPaint(var Message: TWMPaint);
begin
  Include(FControlState, csCustomPaint);
  inherited;
  Exclude(FControlState, csCustomPaint);
end;procedure TButton1.PaintWindow(DC: HDC);
begin
  FCanvas.Lock;
  try
    FCanvas.Handle := DC;
    try
      TControlCanvas(FCanvas).UpdateTextFlags;
      Paint;
    finally
      FCanvas.Handle := 0;
    end;
  finally
    FCanvas.Unlock;
  end;
end;procedure TButton1.Paint;
begin
end;procedure Register;
begin
  RegisterComponents('Samples', [TButton1]);
end;end.