C++ Builder XE2随意学习 (14) > 窗口透明处理

升级图形程序，中间有把窗口逐渐透明化的处理方式。

之前实现方式：

SetLayeredWindowAttributes(Form->Handle, 0, 0, 2);　　// 全透明

SetLayeredWindowAttributes(Form->Handle, 0, 128, 2);　　// 半透明

SetLayeredWindowAttributes(Form->Handle, 0, 255, 2);　　// 不透明

...

在CB XE2中，首先是不认识SetLayeredWindowAttributes，查帮助，在Vcl.Forms下，则实现为

Vcl::Forms::SetLayeredWindowAttributes(Form->Handle, 0, 128, 2);

期望出现半透明效果。

编译都通不过，参数类型不对，修改为

Vcl::Forms::SetLayeredWindowAttributes(unsigned(Form->Handle), 0, 128, 2);

不错，编译通过了，但无法看到效果。

编一段测试代码：

void __fastcall TForm1::FormClick(TObject *Sender) {

　　static int times = 0;

　　times += 10;

　　Vcl::Forms::SetLayeredWindowAttributes(unsigned(Form->Handle), 0, times, 2);

}

运行后单击，无效果，仍然是不透明状。难道是unsigned转换的问题，不得其解。

网上搜索找到一些解决方式：

提问：

I'm using the following code to make a form transparent, but when the application has a VCL style enabled the form is paint with the background color of the VCL style instead of be transparent.

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(varParams:TCreateParams);override;
  public
    {Public declarations }
  end;

var
  Form1:TForm1;

implementation

{$R *.dfm}

procedure TForm1.CreateParams(varParams: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;

解答：

It seems like a bug to me. The VCL Styles use Style hooks to intercept the paint methods and the Windows messages related to these operations, So in this case you must focus your atention in thePaintBackground method of the TFormStyleHook class located in the Vcl.Forms, from here you create a new style hook class (which descends from TFormStyleHook), override the PaintBackgroundmethod, fix the code and finally before to use it call the RegisterStyleHook method to register the Newstyle hook. check this article Fixing a VCL Style bug in the TPageControl and TTabControl components to see an example.

UPDATE Check this sample

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.

The New Style Hook Class

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.

哦！