delphi一个钩子,看不懂了.帮帮我

unit Unit1;interfaceuses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;var
  Form1: TForm1;
  EventArr:array[0..1000]of EVENTMSG;
  EventLog:Integer;
  PlayLog:Integer;
  hHook,hPlay:Integer;
  bDelay:Bool;implementation{$R *.DFM}
Function PlayProc(iCode:Integer;wParam:wParam;lParam:lParam):LRESULT;stdcall;
begin
  Result:=0;
  if iCode < 0 then
    Result := CallNextHookEx(hPlay,iCode,wParam,lParam)
  else if iCode = HC_SYSMODALON then
  //  canPlay:=0
  else if iCode = HC_SYSMODALOFF then
  //  canPlay:=1
  else if (iCode=HC_GETNEXT) then begin
    if bDelay then begin
      bDelay:=False;
      Result:=50;                            \\为什么这里的返回值是50?  
  end;
    pEventMSG(lParam)^:=EventArr[PlayLog];
  end
  else if (iCode = HC_SKIP)then begin
    bDelay := True;
    PlayLog:=PlayLog+1;
  end;
  if PlayLog>=EventLog then begin
    UNHookWindowsHookEx(hPlay);
  end;
end;function HookProc(iCode:Integer;wParam:wParam;lParam:lParam):LRESULT;stdcall;
begin
//  recOK:=1;
  Result:=0;
  if iCode < 0 then
    Result := CallNextHookEx(hHook,iCode,wParam,lParam) \\icode有怎么多个参数,如何知道他传过来的是哪个参数,可能说的不太清楚,我也不太清楚怎么说只是要问当setwindowshookex要调用这个hookproc钩子函数,如何知道他传递过来的icode是什么值.是自动决定的吗?
  else if iCode = HC_SYSMODALON then
//    recOK:=0
  else if iCode = HC_SYSMODALOFF then
//    recOK:=1
  else if (iCode = HC_ACTION) then begin
    EventArr[EventLog]:=pEventMSG(lParam)^;
    EventLog:=EventLog+1;    if EventLog>=1000 then begin
      UnHookWindowsHookEx(hHook);
    end;
  end;
end;procedure TForm1.FormCreate(Sender: TObject);
begin
  Button2.Enabled:=False;
  Button3.Enabled:=False;
end;procedure TForm1.Button1Click(Sender: TObject);
begin
  EventLog:=0;
  hHook:=SetwindowsHookEx(WH_JOURNALRECORD,HookProc,HInstance,0);
  Button2.Enabled:=True;
  Button1.Enabled:=False;
  Button3.Enabled:=False;
end;procedure TForm1.Button3Click(Sender: TObject);
begin
  PlayLog:=0;
  hPlay:=SetwindowsHookEx(WH_JOURNALPLAYBACK,PlayProc,
    HInstance,0);
end;
procedure TForm1.Button2Click(Sender: TObject);
begin
  UnHookWindowsHookEx(hHook);
  hHook:=0;
  Button1.Enabled:=True;
  Button2.Enabled:=False;
  Button3.Enabled:=True;
end;end.
我提的问题都是上边注释提的问题,还有一个不懂.callnexthookex到底把钩子函数传递给谁.因为我看的几个钩子例子都只有一个钩子函数,callnexthookex到底把信息传递给谁了.