Interview questions related to Android exceptions and performance optimization - detailed explanation of ANR exception interview questions

What is ANR?

Application Not Responding

The main reasons for ANR:

The responsiveness of the application is monitored by the ActivityManager and WindowManager system services. When it is monitored that the main thread clicks in the Activity for more than 5 seconds and there is no response or there is no response in the broadcast UI thread for more than 10 seconds, it will cause ANR. Here are the specifics:

• The main thread is blocked by I/O operations (network IO is not allowed in the main thread since 4.0).
• There are time-consuming computations in the main thread.

The main reason for ANR: Which operations are in the main thread in Android?

• All lifecycle callbacks of Activity are executed on the main thread.
• Service is executed on the main thread by default.
• The onReceive callback of BroadcastReceiver is executed on the main thread.
• The handleMessage of the Handler of the looper of the child thread is not used, and post(Runnable) is executed on the main thread.
• Except for doInBackground, the callback of AsyncTask is executed on the main thread.

How to fix ANRs:

• Use Asynctask to handle time-consuming IO operations.
• Use Thread or HandlerThread to increase the priority.
• Use Handler to handle time-consuming tasks of worker threads.
• Try to avoid time-consuming code in the Activity's onCreate() and onResume() callbacks.