GetForegroundWindow 与 GetActiveWindow 的区别 - 回复 "delphier" 的问题

问题来源: http://www.cnblogs.com/del/archive/2008/12/13/1081644.html#1400835

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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．

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代码文件:

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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:

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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