delphi - 如何自定义滚动条颜色？

Question

我找到了一些如下示例代码，用于尝试自定义滚动条颜色：

HBRUSH CMainFrame::OnCtlColor(CDC* pDC, CWnd* pWnd, UINT nCtlColor)       
{ 
   HBRUSH hbr = CFrameWnd::OnCtlColor(pDC, pWnd, nCtlColor); 

   if(nCtlColor==CTLCOLOR_SCROLLBAR) 
      return m_brColor; 

   return hbr; 
}

我发现以下代码不起作用：

procedure TForm1.WMCTLColor(var msg: TWMCTLCOLOR); message WM_CTLCOLOR;

我怎样才能在德尔福中做到这一点？

Answer 1

本机 api 中没有WM_CTLCOLOR消息。相反，您可以使用CN_CTLCOLORSCROLLBAR控件通知，它由 VCL 发送给子控件以响应 API 的WM_CTLCOLORSCROLLBAR.

type
  TScrollBar = class(TScrollBar)
  protected
    procedure WMCtlColor(var Message: TWMCtlColorScrollbar); message CN_CTLCOLORSCROLLBAR;
  end;

procedure TScrollBar.WMCtlColor(var Message: TWMCtlColor);
begin
  Message.Result := CreateSolidBrush(RGB(255, 255, 0));
end;

或者，如果您不想派生新控件，只要将滚动条放在窗体上：

  TForm1 = class(TForm)
    ...
  protected
    procedure WMCtlColorScrollbar(var Message: TWMCtlColorScrollbar);
      message WM_CTLCOLORSCROLLBAR;
    ...
  end;

procedure TForm1.WMCtlColorScrollbar(var Message: TWMCtlColorScrollbar);
begin
  if Message.ChildWnd = ScrollBar1.Handle then
    Message.Result := CreateSolidBrush(RGB(255, 255, 0));
end;

Answer 2

这种改进避免了通过重复调用 CreateSolidBrush() 造成的内存泄漏

{ TMyScrollBar }
//******************************************************************************
constructor TMyScrollBar.Create(AOwner: TComponent);
begin
  inherited;
  FHBrush := CreateSolidBrush(ColorToRGB(FBackColor));
end;

//******************************************************************************
destructor TMyScrollBar.Destroy;
begin
  DeleteObject(FHBrush);
  inherited;
end;

//******************************************************************************
procedure TMyScrollBar.SetBackColor(const Value: Tcolor);
begin
  FBackColor := Value;
  DeleteObject(FHBrush);
  FHBrush := CreateSolidBrush(ColorToRGB(FBackColor));
end;

//******************************************************************************
procedure TMyScrollBar.WMCtlColor(var Message: TWMCtlColorScrollbar);
begin
  Message.Result := FHBrush;
end;