January 2020
Intermediate to advanced
356 pages
6h 4m
Chinese
Content preview from Swift游戏开发经典实例
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106
｜
第
3
章
本节讨论了如何访问设备在
3
个轴上的倾斜；要使用这些信息进行转向，请参考本
章
3.18
节。
在接收运动变更通知时，你可以用
CMMotionManager
的
topDeviceMotionUpdates()
来停止通知。
需要注意一点，苹果文档中警告不要使用主队列，因为通知发送的频率很好。我们
在这里使用主队列的原因仅仅是为了演示，从性能角度考虑，请使用后台队列，参
考问题
1.13
。
3.10
获得指北针方向
问题
如何知道用户正前方是什么方向（相对于正北）？
解决方案
首先，在项目中引入
Core Motion
框架，然后创建一个
CMMotionManager
对象，正
如本章
3.9
节所述。
接着，调用
startDeviceMotionUpdates(using:, to:, withHandler:)
方法，向系
统注册，以便
App
能够接收到设备的移动信息，同时向方法的第一个参数传递一
个
CMAttitudeReferenceFrame.XTrueNorthZVertical
参数：
motionManager.startDeviceMotionUpdates(
using: CMAttitudeReferenceFrame.xTrueNorthZVertical,
to: mainQueue) { (motion, error) in
//
确保
CMDeviceMotion
是有效的
guard let motion = motion else {
if let ...
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