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.
窗体文件:
object Form1: TForm1
Left = 0
Top = 0
Caption = 'Form1'
ClientHeight = 155
ClientWidth = 250
Color = clBtnFace
Font.Charset = DEFAULT_CHARSET
Font.Color = clWindowText
Font.Height = -11
Font.Name = 'Tahoma'
Font.Style = []
OldCreateOrder = False
OnCreate = FormCreate
PixelsPerInch = 96
TextHeight = 13
object Label1: TLabel
Left = 32
Top = 24
Width = 281
Height = 17
Caption = 'Label1'
end
object Label2: TLabel
Left = 32
Top = 47
Width = 281
Height = 17
Caption = 'Label2'
end
object Button1: TButton
Left = 24
Top = 87
Width = 97
Height = 25
Caption = 'Button1'
TabOrder = 0
OnClick = Button1Click
end
object Button2: TButton
Left = 136
Top = 87
Width = 97
Height = 25
Caption = 'Button2'
TabOrder = 1
OnClick = Button2Click
end
object Button3: TButton
Left = 24
Top = 118
Width = 209
Height = 25
Caption = 'Button3'
TabOrder = 2
OnClick = Button3Click
end
object Timer1: TTimer
OnTimer = Timer1Timer
Left = 208
Top = 56
end
end