启用 VCL 样式时如何制作透明表单？

Question

我正在使用以下代码使表单透明，但是当应用程序启用了 VCL 样式时，表单将使用 VCL 样式的背景颜色进行绘制，而不是透明的。

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs;

type
  TForm1 = class(TForm)
    procedure FormShow(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
    procedure CreateParams(var Params:TCreateParams); override;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.CreateParams(var Params: TCreateParams);
begin
 inherited CreateParams(Params);
 Params.ExStyle := WS_EX_TRANSPARENT or WS_EX_TOPMOST;
 //Params.ExStyle := Params.ExStyle or WS_EX_LAYERED;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
 Brush.Style:=bsClear;
 BorderStyle:=bsNone;
 //SetLayeredWindowAttributes(Handle, 0, 230, $00000002);
end;

仅供参考，如果 vcl 样式设置为 Windows，则代码可以正常工作。

是否存在另一种使表单透明以解决此问题的方法？

Answer 1

对我来说这似乎是一个错误。 VCL Styles 使用 Style hooks 来拦截与这些操作相关的绘制方法和 Windows 消息，因此在这种情况下，您必须将注意力集中在位于 TFormStyleHook 类的 PaintBackground 方法上Vcl.Forms，从这里创建一个新的样式钩子类（它继承自TFormStyleHook），覆盖PaintBackground 方法，修复代码，最后在使用它之前调用RegisterStyleHook 方法进行注册新的风格钩子。查看这篇文章Fixing a VCL Style bug in the TPageControl and TTabControl components 以查看示例。

更新 检查此示例

unit Unit138;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs;

type
  TForm138 = class(TForm)
    procedure FormCreate(Sender: TObject);
  private
    procedure CreateParams(var Params:TCreateParams); override;
  public
  end;


var
  Form138: TForm138;

implementation

 Uses
   Vcl.Themes,
   Vcl.Styles,
   uPatch;

{$R *.dfm}

procedure TForm138.CreateParams(var Params: TCreateParams);
begin
 inherited CreateParams(Params);
 Params.ExStyle := WS_EX_TRANSPARENT or WS_EX_TOPMOST;
end;

procedure TForm138.FormCreate(Sender: TObject);
begin
 Brush.Style:=bsClear;
 BorderStyle:=bsNone;
end;

initialization
 TStyleManager.Engine.UnRegisterStyleHook(TForm, TFormStyleHook);//unregister the original style hook
 TStyleManager.Engine.RegisterStyleHook(TForm, TMyStyleHookClass); //register the new style hook

end.

新风格的钩子类

unit uPatch;

interface

uses
  Vcl.Graphics,
  Vcl.Forms;

type
  TMyStyleHookClass= class(TFormStyleHook)
  protected
   procedure PaintBackground(Canvas: TCanvas); override;
  end;

implementation

uses
  Winapi.Windows,
  System.Types,
  Vcl.Themes;


procedure TMyStyleHookClass.PaintBackground(Canvas: TCanvas);
{This is only a basic sample for fix a specific scenario}
var
  Details: TThemedElementDetails;
  R: TRect;
begin
  if StyleServices.Available then
  begin
    if (GetWindowLong(Form.Handle,GWL_EXSTYLE) AND WS_EX_TRANSPARENT) = WS_EX_TRANSPARENT  then
    if Form.Brush.Style = bsClear then Exit;

    Details.Element := teWindow;
    Details.Part := 0;
    R := Rect(0, 0, Control.ClientWidth, Control.ClientHeight);
    StyleServices.DrawElement(Canvas.Handle, Details, R);
  end;
end;

end.

Answer 2

另外，您是否尝试过使用TransparentColor 和TranparentColorValue 属性而不是在CreateParams() 中操作窗口样式？

Answer 3

我使用 OverridePaintNC := False 来防止在 NC 区域上绘制样式。还有 OverrideEraseBkgnd。也许这有帮助。