问题描述
我正在尝试从iPhone的加速度计（我自己的iPhone 5s）中记录数据，并使用字符串（格式：％。2f，数据）其中data是我要记录的特定轴的值。为此，我设置了CMMotionManager并开始记录加速度计数据，我有一个定时器，可以不断更新标签中的文本。但是，我从Xcode收到错误：致命错误：在展开Optional值时意外发现nil。以下是相关代码：
I am trying to record the data from the iPhone's accelerometer (my own iPhone 5s) and set a label on the screen to that data using String(format: "%.2f", data) where data is the value for the specific axis I want to record. To do this I set up a CMMotionManager and began recording accelerometer data, and I have a timer that constantly updates the text in the label. However, I am getting an error from Xcode: "fatal error: unexpectedly found nil while unwrapping an Optional value". Here is the relevant code:
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
//if accelerometer can be used, start it
if (motionManager.accelerometerAvailable) {
motionManager.accelerometerUpdateInterval = 0.1
motionManager.startAccelerometerUpdates()
let timer = NSTimer.scheduledTimerWithTimeInterval(0.1, target: self, selector: Selector("update"), userInfo: nil, repeats: true)
}
}
func update () {
if (motionManager.accelerometerActive) {
accelX.text = String(format: "%.2f", motionManager.accelerometerData.acceleration.x)
}
}
当我将accelX.text赋值更改为简单字符串时，错误停止，因此我认为创建错误的可选变量与加速度计有关。然而，据我所知，如果你有任何建议，或者我完全错了，并且有更好更简单的方法，如果你帮助我，我一定会很感激。
The error stops when I change the accelX.text assignment to a simple string, so I think the optional variable creating the error is something to do with the accelerometer. That's as far as I know, however, so if you have any suggestions, or if I'm doing it completely wrong and there's a better and easier way, I will definitely appreciate it if you help me out.
推荐答案
NSHipster有一篇很好的文章来讨论核心议案：
NSHipster has a good article to talk about the core motion: http://nshipster.com/cmdevicemotion/
使用动态数据定期更新UI的更好方法是使用如下所示的模式如下：
A better way to regularly update UI with motion data is to use the patter as shown in below:
if manager.accelerometerAvailable {
manager.accelerometerUpdateInterval = 0.1
manager.startAccelerometerUpdatesToQueue(NSOperationQueue.mainQueue()) {
[weak self] (data: CMAccelerometerData!, error: NSError!) in
accelX.text = String(format: "%.2f", data.acceleration.x)
}
}
这篇关于如何在iOS中使用Swift正确检索加速计数据？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！