有的时候我们要实现一个悬浮窗口，并使该窗口一直显示在桌面的工作区内。即整个窗口要一直显示在屏幕上，不能超出屏幕的上下左右边缘。此功能的实现也不难，我们需要自己写代码来响应窗口的WM_WINDOWPOSCHANGING消息，话不多说，详细代码如下供参考：
新建一个工程，并把下面代码拷贝到工程中，运行……
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unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs;
type
TForm1 = class(TForm)
private
procedure WMWindowPosChanging(var Message: TWMWindowPosChanging); message WM_WINDOWPOSCHANGING;
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.WMWindowPosChanging(var Message: TWMWindowPosChanging);
begin
inherited;
if (Message.WindowPos.y + Message.WindowPos.cy > Screen.WorkAreaHeight) then begin
Message.WindowPos.Y := Screen.WorkAreaHeight - Height ;
end;
if (Message.WindowPos.x + Message.WindowPos.cx > Screen.WorkAreaWidth) then begin
Message.WindowPos.X := Screen.WorkAreaWidth - Width ;
end;
if Message.WindowPos.x < 0 then
Message.WindowPos.x := 0;
if Message.WindowPos.y < 0 then
Message.WindowPos.y := 0;
end;
end.
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http://bcoder.com/delphi/make-the-window-always-shows-in-desktop-workarea-in-delphi