请教：在delphi中TApplicationEvents控件的用途与使用方法？？？

我来举个简单的例子，dbgrid的滚动条相关的。

dbgrid中假如记录很多，使用鼠标滚动条滚动的时候，只会在dbgrid当前页面数据内滚动，而滚动条是不会动的，这样操作很不方便，需要再拖动滚动条去滚动数据。加了TApplicationEvents就可以去判断事件触发对应的方法。

代码：新建应用程序工程，直接在界面上放个dbgrid，高度不要太高，写form的oncreate事件和TApplicationEvents的onmessage事件。

不放和放TApplicationEvents，你可以看下效果。

unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs,DBClient,DB, Grids, DBGrids, AppEvnts;
type
TForm1 = class(TForm)
DBGrid1: TDBGrid;
ApplicationEvents1: TApplicationEvents;
procedure FormCreate(Sender: TObject);
procedure ApplicationEvents1Message(var Msg: tagMSG;
var Handled: Boolean);
private
{ Private declarations }
cdstemp:TClientDataSet;
ds:TDataSource;
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.FormCreate(Sender: TObject);
var
i:Integer;
begin
//创建对象
cdstemp:=TClientDataSet.Create(Application);
ds:=TDataSource.Create(Application);
//创建dataset列
with cdstemp do
begin
Active:=False;
FieldDefs.Clear;
FieldDefs.Add('id',ftString,32);
CreateDataSet;
Active:=True;
end;
//生成测试数据
for i:=0 to 20 do
begin
cdstemp.Append;
cdstemp.FieldByName('id').AsInteger:=i;
cdstemp.Post;
end;
//绑定
ds.DataSet:=cdstemp;
DBGrid1.DataSource:=ds;
end;
procedure TForm1.ApplicationEvents1Message(var Msg: tagMSG;
var Handled: Boolean);
begin
//先判断焦点在不在DBGrid上
if DBGrid1.Focused then
begin
//判断是不是鼠标滚轮事件
if Msg.message  =  WM_MOUSEWHEEL then
begin
if  Msg.wParam  >  0  then
//滚动条往上滚
SendMessage(DBGrid1.Handle,  WM_KEYDOWN,  VK_UP,  0)
else
//滚动条往下滚
SendMessage(DBGrid1.Handle,  WM_KEYDOWN,  VK_DOWN,  0);
Handled  :=  True;
end;
end;
end;
end.

主要用来拦截应该程序级的事件。主要有：
OnActionExecute;
OnActionUpdate;
OnActivate;
OnDeactivate;
OnException;
OnIdle;
OnHelp;
OnHint;
OnMessage;
OnMinimize;
OnModalBegin;
OnModalEnd;
OnRestore;
OnShowHint;
OnShortCut;
OnShutDown;
OnSettingChange;