When testing and debugging your app, watch for these signs of excessive energy use:

• Battery drain

• Activity when you expect your app to be idle

• An unresponsive or slow user interface

• Large amounts of work on the main thread

• High use of animations

• High use of view opacity

• Swapping

• Memory stalls and cache misses

• Memory warnings

• Lock contention

• Excessive context switches

• Excessive use of timers

• Excessive drawing to screen

• Excessive or repeated small disk I/O

• High-overhead communication, such as network activity with small packets and buffers

• Preventing device sleep

See Which Apps Use Energy on a Device

Users can manage certain energy-related factors, such as screen brightness and active network hardware, by adjusting their device’s settings. They can also open Settings > Battery to see which apps have consumed the most energy recently. See Figure 19-1.

Figure 19-1Battery usage by app in iOS