CMAccelerometerData类V.不推荐使用UIAccelerometer类 [英] CMAccelerometerData class Vs. deprecated UIAccelerometer class

问题描述

根据此文档中， CMAccelerometerData类（位于Core Motion框架中）具有 CMAcceleration 类型的属性 加速 是一个包含3个值（双x，双y，双z）的结构的typedef

Based on this documentation, the CMAccelerometerData class (found in the Core Motion framework) has a property of type CMAcceleration called acceleration that is a typedef of a struct containing 3 values (double x, double y, double z)

我对Objective-C非常陌生）所以我的问题是这样：我的访问，我们说在属性中的 double y 值，在我的代码的某一点？

I'm rather new to Objective-C (I only know C++..) so my question is this : How do I access, let's say the double y value kept in that property, at some point during my code?

我首先如下创建CMAccelerometerData类的实例：

Do I first create an instance of the CMAccelerometerData class like this :

CMAccelerometerData *myAccelerometer;

然后访问其加速属性：

double axisYvalue = [myAccelerometer acceleration]; 

上面显然是错误的，不是吗？我必须得到Y在加速专门发现，那么我该怎么做？

the above is obviously wrong, isn't it? I have to get the Y found in acceleration specifically so how do I do that?

double axisYvalue = [myAccelerometer acceleration->y]; // no this is wrong as well..

那么我该如何做呢？

最后一个问题，如果我可以：）

And one last question if I may :)

给我这个特定的类和属性，现在每次，在我的代码，我使用像

given this specific class and property that I mentioned.. and let's say I've instantiated my CMAccelerometer class.. Now every time, during my code, I use something like

return [myAccelerometer acceleration->y]; // let's say that's the correct version :)

在 的具体时刻获取Y轴的值？

inside some -(double) method .. will I be getting the value of the Y-axis at that specific moment in which the call is being made ?

我问这个，因为我读到有关现在已经过时的UIAccelerometer类，你不得不定义时间间隔，并更新x，y，z的值经常等等等。
现在我可以得到值在加速度属性的调用时刻在Y轴上被执行，不是这种情况？

I am asking this because I got confused when reading about the now deprecated UIAccelerometer class where you had to define intervals and update the values of x,y,z every so often etc.. where as now I can get the value that is being exercised on the Y-axis the moment the call to the acceleration property is made, isn't that the case?

phew ...抱歉的长度的文本！ ：）

phew... sorry for the length of this text! :)

推荐答案

从C ++开始，我认为可以放心地理解指针。第一行：

Coming from C++, I assume it's safe to assume that you understand pointers. That first line:

CMAccelerometerData *myAccelerometer;

...不是创建实例声明指向实例的指针，它不会指向任何有效的。要获得有效的实例，你永远不会自己创建一个。相反，您需要使用 CMMotionManager < a> class' accelerometerData 属性获取指向有效对象的指针：

...isn't creating an instance, it's declaring a pointer to an instance, which won't point to anything valid. To get a valid instance, you'll never actually create one of these yourself. Instead, you'll use the CMMotionManager class' accelerometerData property to get a pointer to a valid object:

// Sometime earlier...
CMMotionManager* manager = [[CMMotionManager alloc] init];
[manager startAccelerometerUpdates];

// Sometime in the present...
// Get a ref to the most recent accelerometer data.
CMAccelerometerData* data = [manager accelerometerData];

// Access it.
double x = [data acceleration].x;

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