today widget NSTimer memory read error?

在today widget里使用NSTimer，发生错误警报:error: memory read failed for 0x0

class TodayViewController: UIViewController, NCWidgetProviding {
    var timer: NSTimer!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view from its nib.
        print("widget")
        
        self.preferredContentSize = CGSizeMake(0,100);

        timer = NSTimer.scheduledTimerWithTimeInterval(5, target: self, selector: Selector(getBattery()), userInfo: nil, repeats: true)
    }
    
    func getBattery() {
        print("level")
    }
    
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
    
    func widgetPerformUpdateWithCompletionHandler(completionHandler: ((NCUpdateResult) -> Void)) {
        // Perform any setup necessary in order to update the view.

        // If an error is encountered, use NCUpdateResult.Failed
        // If there's no update required, use NCUpdateResult.NoData
        // If there's an update, use NCUpdateResult.NewData
        
        completionHandler(NCUpdateResult.NewData)
    }
    
    deinit {
        timer.invalidate()
    }
}

---

做下猜测：
1、error: memory read failed for 0x0。 0x0这个是被释放掉的对象，大意就是对象释放了然后还调用，所以出错了
2、deinit {

    timer.invalidate()
}

deinit相当于dealloc,应该是先去掉timer才会解除自身的循环引用，才会释放，才会调用deinit吧。感觉这里有点问题。在一个合适的时机，暂停timer，然后timer设为nil.看看这下行不行