[iOS] acceleration data

面對手機的直立模式下 (portrait mode)
三軸 (three axes could be positive or negative)

X軸 horizontal across
y軸 vertical across
z軸 runs through from front to back

Two primary classes

• UIAccelerometer
• UIAcceleration

How to utilize UIAccelerometer
3 steps

1. Get the shared accelerometer object
2. Config the delivery interval (default 100 times/second)
3. Set the delegate 
• object to receive acceleration events
• data is sent to the main thread repeatedly until removed.

How to utilize UIAcceleration
store the data associated with an acceleration event
read-only properties x, y, z