delphi GetForegroundWindow 与 GetActiveWindow 的区别

GetActiveWindow 只是获取当前程序中(严格地说是线程中)被激活的窗口;

GetForegroundWindow 是获取当前系统中被激活的窗口.

两个函数的级别不一样, 一个是线程级、一个是系统级.

被激活的窗口不一定是顶层窗口(最上面的窗口).

下面的例子可以充分说明问题, 测试方法：点击三个按钮，然后反复切换焦点、观察．

代码文件:

unit Unit1;

interface

uses

Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

Dialogs, StdCtrls, ExtCtrls;

type

TForm1 = class(TForm)

Timer1: TTimer;

Label1: TLabel;

Label2: TLabel;

Button1: TButton;

Button2: TButton;

Button3: TButton;

procedure Button1Click(Sender: TObject);

procedure Timer1Timer(Sender: TObject);

procedure Button2Click(Sender: TObject);

procedure FormCreate(Sender: TObject);

procedure Button3Click(Sender: TObject);

end;

var

Form1: TForm1;

implementation

{$R *.dfm}

var

i: Integer;

procedure TForm1.Timer1Timer(Sender: TObject);

var

buf: array[Byte] of Char;

begin

GetWindowText(GetActiveWindow, buf, Length(buf)*SizeOf(buf[0]));

Label1.Caption := 'GetActiveWindow: ' + buf;

GetWindowText(GetForegroundWindow, buf, Length(buf)*SizeOf(buf[0]));

Label2.Caption := 'GetForegroundWindow: ' + buf;

end;

procedure TForm1.Button1Click(Sender: TObject);

var

frm: TForm1;

begin

Inc(i);

frm := TForm1.Create(Self);

frm.FormStyle := fsNormal;

frm.Text := Format('Normal %d', [i]);

frm.Show;

end;

procedure TForm1.Button2Click(Sender: TObject);

var

frm: TForm1;

begin

Inc(i);

frm := TForm1.Create(Self);

frm.FormStyle := fsStayOnTop;

frm.Text := Format('StayOnTop %d', [i]);

frm.Show;

end;

procedure TForm1.Button3Click(Sender: TObject);

begin

WinExec('notepad.exe', SW_NORMAL);

WinExec('calc.exe', SW_NORMAL);

end;

procedure TForm1.FormCreate(Sender: TObject);

begin

Timer1.Interval := 100;

Button1.Caption := '建立一般窗口';

Button2.Caption := '建立顶层窗口';

Button3.Caption := '启动记事本和计算器';

end;

end.

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