鼠标进入与离开的消息（使用CM_MOUSEENTER来判断是否进入控件）

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unit Unit1;

interface

uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
StdCtrls;

type
TForm1 = class(TForm)
    Label1: TLabel;
    Button1: TButton;
    Edit1: TEdit;
private
    { Private declarations }
    procedure CMMouseEnter(var Msg: TMessage); message CM_MOUSEENTER;
    procedure CMMouseLeave(var Msg: TMessage); message CM_MOUSELEAVE;

public
{ Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.CMMouseEnter(var Msg: TMessage);
var
anObject :        TObject;
begin
anObject := TObject(Msg.lParam);
//进入控件
if anObject <> nil then
begin
    Label1.Caption := 'Mouse Enter...'; //显示信息
end;
end;
procedure TForm1.CMMouseLeave(var Msg: TMessage);
//退出控件
var
anObject :        TObject;
begin
anObject := TObject(Msg.lParam);
if anObject <> nil then
begin
       Label1.Caption := 'Mouse Leave...'; //显示信息
end;
end;