VCL控件组件大都应该重载TWinControl的虚函数WndProc来进行处理窗口消息的工作

TWinControl的构造函数中会调用MakeObjectInstance并且传递MainWndProc作为窗口消息处理函数，而MainWndProc则会调用虚函数WndProc来处理窗口消息。留个爪，对TButton的主要方法，都要仔细解读一下。

推测VCL控件组件大都应该重载TWinControl的虚函数WndProc来进行处理窗口消息的工作，举例：

procedure TButtonControl.WndProc(var Message: TMessage); override;
begin
  case Message.Msg of
    WM_LBUTTONDOWN, WM_LBUTTONDBLCLK:
      if not (csDesigning in ComponentState) and not Focused then
      begin
        FClicksDisabled := True;
        Windows.SetFocus(Handle); // Windows单元
        FClicksDisabled := False;
        if not Focused then Exit;
      end;
    CN_COMMAND:
      if FClicksDisabled then Exit;
  end;
  inherited WndProc(Message);

  TButtonControl = class(TWinControl)
  private
    FClicksDisabled: Boolean;
    FWordWrap: Boolean;
    function IsCheckedStored: Boolean;
    procedure CNCtlColorStatic(var Message: TWMCtlColorStatic); message CN_CTLCOLORSTATIC;
    procedure WMEraseBkGnd(var Message: TWMEraseBkGnd); message WM_ERASEBKGND;
    procedure SetWordWrap(const Value: Boolean);
  protected
    procedure ActionChange(Sender: TObject; CheckDefaults: Boolean); override;
    function GetActionLinkClass: TControlActionLinkClass; override;
    function GetChecked: Boolean; virtual;
    procedure SetChecked(Value: Boolean); virtual;
    procedure WndProc(var Message: TMessage); override;
    procedure CreateParams(var Params: TCreateParams); override;
    property Checked: Boolean read GetChecked write SetChecked stored IsCheckedStored default False;
    property ClicksDisabled: Boolean read FClicksDisabled write FClicksDisabled;
    property WordWrap: Boolean read FWordWrap write SetWordWrap default False;
  public
    constructor Create(AOwner: TComponent); override;
  end;

  TButton = class(TButtonControl)
  private
    FDefault: Boolean;
    FCancel: Boolean;
    FActive: Boolean;
    FModalResult: TModalResult;
    procedure SetDefault(Value: Boolean);
    procedure CMDialogKey(var Message: TCMDialogKey); message CM_DIALOGKEY;
    procedure CMDialogChar(var Message: TCMDialogChar); message CM_DIALOGCHAR;
    procedure CMFocusChanged(var Message: TCMFocusChanged); message CM_FOCUSCHANGED;
    procedure CNCommand(var Message: TWMCommand); message CN_COMMAND;
    procedure CNCtlColorBtn(var Message: TWMCtlColorBtn); message CN_CTLCOLORBTN;
    procedure WMEraseBkgnd(var Message: TWMEraseBkgnd); message WM_ERASEBKGND;
  protected
    procedure CreateParams(var Params: TCreateParams); override;
    procedure CreateWnd; override;
    procedure SetButtonStyle(ADefault: Boolean); virtual;
  public
    constructor Create(AOwner: TComponent); override;
    procedure Click; override;
    function UseRightToLeftAlignment: Boolean; override;
end;

// TButtonControl 研究

constructor TButtonControl.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  if SysLocale.FarEast and (Win32Platform = VER_PLATFORM_WIN32_NT) then
    ImeMode := imDisable;
end;

procedure TButtonControl.ActionChange(Sender: TObject; CheckDefaults: Boolean);
begin
  inherited ActionChange(Sender, CheckDefaults);
  if Sender is TCustomAction then
    with TCustomAction(Sender) do
    begin
      if not CheckDefaults or (Self.Checked = False) then
        Self.Checked := Checked;
    end;
end;

function TButtonControl.GetActionLinkClass: TControlActionLinkClass;
begin
  Result := TButtonActionLink;
end;

function TButtonControl.IsCheckedStored: Boolean;
begin
  Result := (ActionLink = nil) or not TButtonActionLink(ActionLink).IsCheckedLinked;
end;

procedure TButtonControl.CNCtlColorStatic(var Message: TWMCtlColorStatic);
begin
  with ThemeServices do
    if ThemesEnabled then
    begin
      DrawParentBackground(Handle, Message.ChildDC, nil, False);
      { Return an empty brush to prevent Windows from overpainting we just have created. }
      Message.Result := GetStockObject(NULL_BRUSH);
    end
    else
      inherited;
end;

procedure TButtonControl.WMEraseBkGnd(var Message: TWMEraseBkGnd);
begin
  { Under theme services the background is drawn in CN_CTLCOLORSTATIC. }
  if ThemeServices.ThemesEnabled then
    Message.Result := 1
  else
    inherited;
end;

procedure TButtonControl.CreateParams(var Params: TCreateParams);
begin
  inherited;
  if FWordWrap then
    Params.Style := Params.Style or BS_MULTILINE;
end;

procedure TButtonControl.SetWordWrap(const Value: Boolean);
begin
  if FWordWrap <> Value then
  begin
    FWordWrap := Value;
    RecreateWnd;
  end;
end;

// TButton研究

constructor TButton.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  ControlStyle := [csSetCaption, csDoubleClicks];
  Width := 75;
  Height := 25;
  TabStop := True;
end;

procedure TButton.Click;
var
  Form: TCustomForm;
begin
  Form := GetParentForm(Self);
  if Form <> nil then Form.ModalResult := ModalResult;
  inherited Click;
end;

function TButton.UseRightToLeftAlignment: Boolean;
begin
  Result := False;
end;

procedure TButton.SetButtonStyle(ADefault: Boolean);
const
  BS_MASK = $000F;
var
  Style: Word;
begin
  if HandleAllocated then
  begin
    if ADefault then Style := BS_DEFPUSHBUTTON else Style := BS_PUSHBUTTON;
    if GetWindowLong(Handle, GWL_STYLE) and BS_MASK <> Style then
      SendMessage(Handle, BM_SETSTYLE, Style, 1);
  end;
end;

procedure TButton.SetDefault(Value: Boolean);
var
  Form: TCustomForm;
begin
  FDefault := Value;
  if HandleAllocated then
  begin
    Form := GetParentForm(Self);
    if Form <> nil then
      Form.Perform(CM_FOCUSCHANGED, 0, Longint(Form.ActiveControl));
  end;
end;

procedure TButton.CreateParams(var Params: TCreateParams);
const
  ButtonStyles: array[Boolean] of DWORD = (BS_PUSHBUTTON, BS_DEFPUSHBUTTON);
begin
  inherited CreateParams(Params);
  CreateSubClass(Params, 'BUTTON');
  Params.Style := Params.Style or ButtonStyles[FDefault];
end;

procedure TButton.CreateWnd;
begin
  inherited CreateWnd;
  FActive := FDefault;
end;

procedure TButton.CNCommand(var Message: TWMCommand);
begin
  if Message.NotifyCode = BN_CLICKED then Click;
end;

procedure TButton.CMDialogKey(var Message: TCMDialogKey);
begin
  with Message do
    if  (((CharCode = VK_RETURN) and FActive) or
      ((CharCode = VK_ESCAPE) and FCancel)) and
      (KeyDataToShiftState(Message.KeyData) = []) and CanFocus then
    begin
      Click;
      Result := 1;
    end else
      inherited;
end;

procedure TButton.CMDialogChar(var Message: TCMDialogChar);
begin
  with Message do
    if IsAccel(CharCode, Caption) and CanFocus then
    begin
      Click;
      Result := 1;
    end else
      inherited;
end;

procedure TButton.CMFocusChanged(var Message: TCMFocusChanged);
begin
  with Message do
    if Sender is TButton then
      FActive := Sender = Self
    else
      FActive := FDefault;
  SetButtonStyle(FActive);
  inherited;
end;

procedure TButton.WMEraseBkgnd(var Message: TWMEraseBkgnd);
begin
  if ThemeServices.ThemesEnabled then
    Message.Result := 1
  else
    DefaultHandler(Message);
end;

procedure TButton.CNCtlColorBtn(var Message: TWMCtlColorBtn);
begin
  with ThemeServices do
    if ThemesEnabled then
    begin
      DrawParentBackground(Handle, Message.ChildDC, nil, False);
      { Return an empty brush to prevent Windows from overpainting we just have created. }
      Message.Result := GetStockObject(NULL_BRUSH);
    end
    else
      inherited;
end;

其它继承的组件：
TCustomCheckBox = class(TButtonControl)
TCheckBox = class(TCustomCheckBox)
TRadioButton = class(TButtonControl)