delphi 多线程定时执行程序如何写

unit Unit1;
 
interface
 
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs;
 
type
  TSysChatMainForm = class(TForm)
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
    FTestNetThread: TThread;
  public
    { Public declarations }
  end;
 
var
  SysChatMainForm: TSysChatMainForm;
 
implementation
 
{$R *.dfm}
 
type
  TTestNetThread = class(TTHread)
    procedure Execute; override;
    procedure RefreshUIInMainThread;
  end;
 
{ TTestNetThread }
 
procedure TTestNetThread.RefreshUIInMainThread;
begin
  bsTrayIcon.ShowBalloonHint('网络异常','由于网络异常，程序掉线！',bsbitInfo);
end;
 
procedure TTestNetThread.Execute;
begin
  inherited;
  FreeOnTerminate := True;
 
  while (not Terminated) and (not InternetGetConnectedState(nil, 0)) then
  begin
    Data.UserOff('[脱机]',false);
    Synchronize(RefreshUIInMainThread);
 
    Sleep(3000)
  end;
end;
 
{ TSysChatMainForm }
 
procedure TSysChatMainForm.FormCreate(Sender: TObject);
begin
  FTestNetThread := TTestNetThread.Create(False);
end;
 
procedure TSysChatMainForm.FormDestroy(Sender: TObject);
begin
  FTestNetThread.Terminate;
end;
 
end.