var
  ADOCon: TADOConnection;
begin
  //to do 创建ADOCon对象，并为ADOCon赋值连接字符串，代码省略
 
  ADOCon.KeepConnection := false;
  //此时网络连接正常
  ADOCon.Open;  //或者ADOCon.Connected := true;
  ADOCon.Connected; //该属性值为true
  //断开网络连接
  ADOCon.Connected; //该属性值为true
  ADOCon.Open; //此时连接出现异常
  ADOCon.Connected; //该属性值为false
end;

procedure TForm1.tmr1Timer(Sender: TObject);
  function TestConnected: Boolean;
  var
    aCon: TADOConnection;
  begin
    Result := False;
    aCon := TADOConnection.Create(nil); //创建临时对象
    try
      aCon.ConnectionString := const_DBCON_MYSQL; //连接字符串
      try
        aCon.Connected := True;
        Result := True;
      except
        Exit;
      end;
    finally
      aCon.Free;
    end;
  end;
begin
  if not TestConnected then //使用临时对象判断数据库连接状况
  begin
    FADOCon.Close; //根据临时对象连接状况操作连接对象，若无法连接则关闭连接对象，若连接正常则打开连接对象
  end
  else
  begin
    if FADOCon.Connected then
      FADOCon.Connected := True;
  end;
end;

procedure TForm1.btn3Click(Sender: TObject);
begin
  try
    FADOQuery.Close;
    FADOQuery.Connection := FADOCon;
    FADOQuery.SQL.Text := 'select * from fp_kpxx';
    FADOQuery.Open; //连接对象关闭状态下，查询时会自动连接
    ShowInfoDlg(IntToStr(FADOQuery.RecordCount));
    FADOCon.Close;
    //此时断开网络
     FADOQuery.Open; //此时出现异常
     FADOCon.Close;
    //此时恢复网络
     FADOQuery.Open; //此时查询正常
     FADOCon.Close;
  except
    ShowInfoDlg('查询失败');
  end;
end;