====== Building Battery-Conscious Apps ======

Das ist mein Konspekt von dem Online-Kurs [[https://www.linkedin.com/learning/android-development-building-battery-conscious-apps|Android Development: Building Battery-Conscious Apps]]\\ 

===== Introduction =====

==== Why be battery conscious? ====
...

===== 1. Basics of Battery Usage =====

==== Principles of battery-concious apps ====

https://www.linkedin.com/learning/android-development-building-battery-conscious-apps/principles-of-battery-conscious-apps

Wake-Up has costs:
  * CPU on
  * Screen on
  * Data (Wi-Fi or cellular) on

Official documentation: http://developer.android.com/topic/performance/power/#lazy

Smart Design (aka Lazy First design)
  - Reduce (e.g. resolution of photos for upload/download)
  - Defer
  - Coalesce (combining transactions to a "batch")
  - Rethink
  

===== 2. Battery Drain and Workarounds =====


==== Considerations for using AlarmManager ====
https://www.linkedin.com/learning/android-development-building-battery-conscious-apps/considerations-for-using-alarmmanager

  * Schedule asynchronous operations
  * Time-based
  * Single or repetitive
  * Perfect for exact time-based scheduling
  * Periodic background tasks
  * Combined effects cause battery drain
  * Wake up has a cost

==== Pitfalls of poor AlarmManager usage ====
https://www.linkedin.com/learning/android-development-building-battery-conscious-apps/pitfalls-of-poor-alarmmanager-usage

  - Background network operations (AlarmManager does not have intelligent dispatch logic)
  - Alarms does not survive reboots (Extra logic required, e.g. BroadcastReceiver)
  - Exact Alarm may not be exact
    * Since Kitkat
    * setExactAndAllowWhileIdle -> is affected by Doze Mode 
  - Doze Mode introduces complexity (e.g. ''setExact'' can drift)
  
Takeaways:
  * Avoid network operations
  * Doze Mode affects AlarmManager
  * Maybe better would be to switch to JobScheduler (because it is not time driven, but event driven)
  
==== Considerations for using background-started services ====
https://www.linkedin.com/learning/android-development-building-battery-conscious-apps/considerations-for-using-background-started-services
  * Background Started Services
    * typically long running operations with no UI (e.g. music player)
    * started via an API call
    * contract:
      * client calls **Context.startService()**
      * system calls **Service.onStartCommand()**
      * Service stops
        * service stops itself with **Service.stopSelf()**
        * OR: 
        * client calls **Service.stopService()**
    * System requires service to remain running until stopped explicitly
    * Note: in production **IntentService** would be better as simple **Service**
  * When to Use Background Started Service
    * intense, low-priority tasks not noticed by user
    * irregular, user-driven background tasks
    * stateless reentrant operations (e.g. refreshing news content)
    * work queue processor pattern (IntentService)
    * Note: if task is periodic scheduled job may be a better choice
==== Pitfalls of poor background-started service usage ====
https://www.linkedin.com/learning/android-development-building-battery-conscious-apps/pitfalls-of-poor-background-started-service-usage

  * Pitfall 1: Android
    * Google is tightening restrictions
  * Pitfall 2: No Rules or Policy Support
    * Connectivity checks
      * Active connection
      * Airplane mode
      * Remote server availability
    * Appropriateness checks
      * Battery level
      * Roaming status
      * Metered connection  
    * Back off and retry policy
      * Retry when?
      * Retry how often?
  * Pitfall 3: No intelligent batching 
    * No batching unlike AlarmManager
    * Cannot differentiate between services and different apps
  * Pitfall 4: Other reasons
    * Idle processes are wasteful
    * Fragmentation is a problem

  * Takeaway
    * Use job scheduler for most cases
    * Use started services for simple one-shot background tasks

==== A review of broadcast receivers ====
https://www.linkedin.com/learning/android-development-building-battery-conscious-apps/a-review-of-broadcast-receivers
  * Introduction to Broadcast Receivers
    * support event-driven programming
    * used for many system events
    * Interprocess communication (IPC)
    * delivered via Intent
    * Intents specify actions and optional extras
    * should extend **BroadcastReceiver**
    * should implement **onReceive()**

==== Registering a broadcast receiver ====
https://www.linkedin.com/learning/android-development-building-battery-conscious-apps/registering-a-broadcast-receiver
  * Statically registered (AndroidManifest.xml)
  * Dynamically registered (through the Java code)

==== Triggering a broadcast receiver ====

https://www.linkedin.com/learning/android-development-building-battery-conscious-apps/triggering-a-broadcast-receiver

Two posibilities to trigger a broadcast receiver:
  - Call implicit trigger
    * Candidates matched via filter
    * Recipients unknown until match
    * Recipients may change 
  - Explicit trigger
    * Invocation via code
    * Recipients known
    * Recipients never change
  
  * Any app can define its own intent

Example of triggering explicitly:
<code java>
Intent i = new Intent("my.action.name")
                .setComponent(new ComponentName(context.getPackageName(), className));
context.setBroadcast(i);
</code> 

==== Considerations of static implicit broadcast receivers ====
https://www.linkedin.com/learning/android-development-building-battery-conscious-apps/considerations-of-static-implicit-broadcast-receivers

===== Post Scriptum =====

This post scriptum is not based on the online course, but on other articles.

==== Intent to the settings, where you can move your app to the whitelist ====
From [[https://proandroiddev.com/android-battery-optimization-for-avoiding-doze-mode-and-app-standby-83cd379ee75b|Android Battery Optimization for Avoiding Doze Mode and App Standby]]
<code java>
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
    Intent intent = new Intent();
    String packageName = getPackageName();
    PowerManager pm = (PowerManager) getSystemService(POWER_SERVICE);
    if (!pm.isIgnoringBatteryOptimizations(packageName)) {
        intent.setAction(Settings.ACTION_REQUEST_IGNORE_BATTERY_OPTIMIZATIONS);
        intent.setData(Uri.parse("package:" + packageName));
        startActivity(intent);
    }
}
</code>