Delphi没有MouseEnter与MouseLeave的事件，网上说可以响应CM_MOUSEENTER和CM_MOUSELEAVE消息来实现。这两个消息是VCL自己定义的消息，看了Delphi的Controls.pas果然看到有以下两行：
CM_MOUSEENTER = CM_BASE + 19;
CM_MOUSELEAVE = CM_BASE + 20;
其中CM_BASE = $B000
可以有两种方式来利用：
方式一：在自定义的控件中添加响应事件来实现
方式二：直接让窗体响应事件，然后判断不同的控件
以下代码从网上参考后修改并运行通过。
unit Unit1; interface uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, ExtCtrls; type
TMyPanel=class(tpanel)
public
procedure MSGEnter(var msg:TMessage);message CM_MOUSEENTER;//响应进入的消息
procedure MSGLeave(var msg: TMessage);message CM_MOUSELEAVE;//响应离开的消息
end; TForm1 = class(TForm)
Panel1: TPanel;
Panel2: TPanel;
procedure FormCreate(Sender: TObject);
private
MYpanel:TMyPanel;
panel:tpanel;
procedure MSGEnter(var msg:TMessage);message CM_MOUSEENTER;//响应进入的消息
procedure MSGLeave(var msg: TMessage);message CM_MOUSELEAVE;//响应离开的消息
{ Private declarations }
public
{ Public declarations }
end; var
Form1: TForm1; implementation {$R *.dfm}
//方式一:对自定义控件定义事件
{ TMyPanel }
procedure TMyPanel.MSGEnter(var msg: TMessage);
begin
Color:=clyellow;
end;
procedure TMyPanel.MSGLeave(var msg: TMessage);
begin
Color:=clred;
end; { TForm1 }
procedure TForm1.FormCreate(Sender: TObject);
begin
MyPanel:=TMyPanel.Create(self);
MyPanel.Parent:=self;
MyPanel.Caption:='鼠标进入变黄, 鼠标离开变红'; Panel:=TPanel.Create(self);
Panel.Parent:=self;
panel.top:=;
end; //方式二:用窗体事件事响应并进行判断
procedure TForm1.MSGEnter(var msg: TMessage);
var
myobj : TObject;
begin
myobj := TObject(msg.LParam);//用LParam进行判断鼠标进入了哪个控件
if (myobj <> nil) and (myobj is TPanel) then
TPanel(myobj).Caption := 'enter';
end; procedure TForm1.MSGLeave(var msg: TMessage);
var
myobj : TObject;
begin
myobj := TObject(msg.LParam);
if (myobj <> nil) and (myobj is TPanel) then
TPanel(myobj).Caption := 'leave';
end; end.
如果想在设计阶段能直接添加事件以做响应，可以自定义控件并将其注册为可视化控件。
方法如下：（以下代码未经测试）
unit MyEdit; interface uses
Classes, Controls, Messages, StdCtrls; type
TMyEdit = class(TEdit)
private
FOnMouseLeave: TNotifyEvent;
FOnMouseEnter: TNotifyEvent;
published
property OnMouseEnter: TNotifyEvent read FOnMouseEnter write FOnMouseEnter;
property OnMouseLeave: TNotifyEvent read FOnMouseLeave write FOnMouseLeave;
procedure CMMouseEnter(var Msg:TMessage);message CM_MOUSEENTER;
procedure CMMouseLeave(var Msg:TMessage);message CM_MOUSELEAVE;
end; procedure Register; implementation procedure Register;
begin
RegisterComponents('Standard', [TMyEdit]);
end; { TMyEdit } procedure TMyEdit.CMMouseEnter(var Msg: TMessage);
begin
inherited;
if Assigned(FOnMouseEnter) then
FOnMouseEnter(Self);
end; procedure TMyEdit.CMMouseLeave(var Msg: TMessage);
begin
inherited;
if Assigned(FOnMouseLeave) then
FOnMouseLeave(Self);
end; end.