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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108
｜
第
3
章
CMAttitudeReferenceFrame.XMagneticNorthZVertical
偏航角的零点指向正北角。
CMAttitudeReferenceFrame.XTrueNorthZVertical
偏航角的零点设置为正北角。同时，系统会使用定位系统。
如果我们需要最精确的数据，应该使用最后一个选项。这个选项最耗电量，同时也
最耗时。如果你不是太在乎到底哪个方向是北，使用
CMAttitudeReferenceFrame.
XArbitraryZVertical
选项或者
CMAttitudeReferenceFrame.
XArbitraryCorrectedZVertical
选项就可以了。
3.11
获得用户的位置
问题
如何获知用户当前的地理位置。
解决方案
当你想使用用户的位置信息时，你应该向用户说明你使用这些信息的目的是什么：
1.
在项目导航窗口（位于
Xcode
窗口的左边）中，点击顶部的项目文件，打开项
目的
Info
窗口。
2.
从
Targets
列表中选中该项目的
target
。
3.
点击
Info
标签。
4.
在设置列表中添加一个新条目“
Privacy - Location Usage Description
”，类型
为
String
，在
Value
一栏里填入你向用户解释的内容，比如用户的坐标信息的
用途之类的（例如在我们的例子中，我们可能会填写“这个程序将会显示你的
坐标”）。
你需要向用户说明应用程序使用用户位置信息的用途：
•
如果
App
只在运行时才使用用户位置信息（也就是说程序在前台的时候），你 ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.