dispatch、wndproc是VCL framework在TWinCtronl定义的虚拟方法，下面程序通过重写（override）这两函数拦截WM_LBUTTONDOWN消息，来与Application.OnMessage事件比较，测试消息流程的先后顺序。
一、程序代码
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;
type
TForm1 = class(TForm)
ListBox1: TListBox;
Button1: TButton;
Button2: TButton;
Button3: TButton;
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject); procedure Button3Click(Sender: TObject); procedure FormCreate(Sender: TObject); private { Private declarations } public procedure WndProc(var AMessage: TMessage); override; procedure dispatch(var AMessage); override; procedure FonMessage(var AMessage: TMsg;var Handled: Boolean); procedure AppMsg(Info: string); { Public declarations } end; var Form1: TForm1; implementation {$R *.dfm} procedure TForm1.AppMsg(Info: string); begin ListBox1.Items.Add(Info); ListBox1.Items.Add('-------------'); ListBox1.Perform(WM_VSCROLL,SB_BOTTOM,0); end; procedure Tform1.WndProc(var AMessage: TMessage); begin inherited; if AMessage.Msg = WM_LBUTTONDOWN then AppMsg('WndProc½Óµ½ÁËÐÅÏ¢'); end; procedure Tform1.dispatch(var AMessage); begin inherited; if Tmessage(AMessage).Msg = WM_LBUTTONDOWN then AppMsg('dispatch½Óµ½ÁËÐÅÏ¢'); end; procedure Tform1.FonMessage(var AMessage: TMsg;var Handled: Boolean); begin if Amessage.message = WM_LBUTTONDOWN then AppMsg('AppOnMessage½Óµ½ÐÅÏ¢'); end; procedure TForm1.Button1Click(Sender: TObject); begin SendMessage(Handle, WM_LBUTTONDOWN, 0, 0); end; procedure TForm1.Button2Click(Sender: TObject); begin PostMessage(Handle, WM_LBUTTONDOWN, 0, 0); end; procedure TForm1.Button3Click(Sender: TObject); begin Self.Perform(WM_LBUTTONDOWN, 0, 0); end; procedure TForm1.FormCreate(Sender: TObject); begin Application.OnMessage:=FonMessage; end; end.
二、程序界面
从程序运行结果来看，Application.OnMessage先拦截到消息，然后是dispatch，最后才是wndproc方法。