Timer、TimerTask间隔无法停止

1、我在项目中遇到一个问题就是timer已经置为null,但是间隔并没有停止，那是因为TimerTask也是需要置为null

private Timer timer;
private TimerTask timertask;

public  void renderInfo(){
    timer = new Timer();
    timertask = new  TimerTask (){
                  @Override
                    public void run() {
                        runOnUiThread(new Runnable() {
                            @Override
                            public void run() {
                                long m = System.currentTimeMillis() / 1000;
                                if (m >= data.getStarttime()) {
                                    .....业务逻辑......
                                    if(mtimertask!=null){
                                        mtimertask.cancel();
                                        mtimertask = null;
                                    }
                                    if (timer != null) {
                                        timer.cancel();
                                        timer = null;
                                    }
                                }

                            }
                        });
                    }
    }

} 
timer.schedule(mtimertask, 0, 1000);