I'm writing an app with alarm functionality, i.e. it will have to continue running while the device goes into standby. Apparently, this is not the case. How can I achieve that?
It would be even better if I could prevent the device from going into standby at all - can I do that?
Android applications can prevent the device from going into standby with a wake lock but this should be used only for short periods of time for specific tasks which require the user to look at the screen without touching it.
For any other long time purposes, you have to use the system AlarmManager to schedule future actions of your application.
Using a permanent wake lock would make your app a battery drainer.
A service runs always, even in standby, so you should use it.
Preventing standby can be done with a wake lock. Be careful, there are only a few apps that should prevent standby (like games, video players...).
Related
According to Android docs:
A Service is an application component representing either an application's desire to perform a longer-running operation while not interacting with the user or to supply functionality for other applications to use.
But my service get killed very quickly - around 10 seconds - when the user leaves the app or the screen gets turn off. It seems according to Android Kotlin Foreground Service stops after some time that you need some sort of mechanism to prevent the phone from getting in doze mode.
So, what is the purpose of having a service without a wake lock? And why does the documentation never mention something remotely related to wake lock when dealing with services?
You can have a Service that is doing work for an Activity. If the user navigates away from the app or dims the screen or ignores his phone long enough for it to be clear that he isn't looking at it, what is the point of the Service continuing to run? The user isn't looking at the Activity, so processing in the Service is not important enough to keep the phone from sleeping.
On the other hand, if you have a Service that is performing important work and you need to keep the phone from going to sleep, then you obviously need to get some kind of wake lock or use some other method to keep the phone on.
These are 2 different scenarios with different requirements.
I have some questions concerning wake lock and services
1- I try to test my service when the screen is off and not acquiring the wake lock, i was expecting that system will kill my service but it didn't happen, so what is the purpose of wake lock?
2- I want to know when then the system goes into doze mode, is it when i turn off the screen or after some time of turning it off? and what happens to my service in this case? and how to know that the system is in doze mode?
3- I know that since Android O normal background service will be killed after nearly one minute, i tried to test that by making intent service and make it running for more than one minute, it was already killed but started again and continued execution, so what is the purpose of killing it and starting it again?
4- does doze mode affect foreground service? and should i acquire wake lock in case of foreground service or is it acquired by default?
Code of Intent service
Logcat
I know they are lots of questions but i am confused with these topics
thanks in advance
The device may fall asleep if the user is inactive and nothing is keeping the device awake. A WakeLock is used to ensure the device stays awake.
You may check those links for additional information: Good answer Official Documentation
Information about Doze mode, Standby and some other things that you may be interested in:
link
Background Service Limitations: While an app is idle, there are limits to its use of background services. This does not apply to foreground services, which are more noticeable to the user.
link
Processes which have a current running foreground service are supposed to be unaffected by Doze. Bound/unbound, started/not-started, and wakelocks do not affect this whitelisting process.
link
--- Update ---
Some things could change from the moment of those questions were asked, so prefer to read documentation or search for the actual information about it. Also it's a good idea to check information about modern solutions for back ground like WorkManager.
Let's say an Android application acquires a wake-lock, and then launches another application by sending it an explicit intent. Does the effect of acquisition of wake-lock last while the other application is in the foreground ?
As described in Keeping the Device Awake it's perfectly natural for a background application to grab and hold a CPU wakelock:
One legitimate case for using a wake lock might be a background service that needs to grab a wake lock to keep the CPU running to do work while the screen is off. Again, though, this practice should be minimized because of its impact on battery life.
This action is pretty common. For example, imagine a music playing application. Even though the screen is off, or some other activity is in the foreground, it's fine for a background application to hold a wake lock to keep playing music.
Although that last line should really take a warning. As described in Wakelocks and Battery Drain those things tend to burn through battery pretty fast; and worse yet, is that it's a pretty common problem to not release them properly, and end up putting the device into a sleepless mode, where it never goes to sleep.
If I have an IntentService that simply updates the SharedPreference, is a (partial) WakeLock needed?
I understand that a WakeLock keeps the CPU awake, but when is it needed?
If you need to keep the CPU running in order to complete some work before the device goes to sleep, you can use a PowerManager system service feature called wake locks. Wake locks allow your application to control the power state of the host device.
Creating and holding wake locks can have a dramatic impact on the host device's battery life. Thus you should use wake locks only when strictly necessary and hold them for as short a time as possible. For example, you should never need to use a wake lock in an activity.
One legitimate case for using a wake lock might be a background service that needs to grab a wake lock to keep the CPU running to do work while the screen is off. Again, though, this practice should be minimized because of its impact on battery life.
Unfortunately, some poorly-coded, malicious, or simply buggy apps might create an abnormal amount of undesirable wakelocks. Other apps require constant Internet access in order to operate in a normal fashion - Facebook and Messenger are probably the most popular representatives. They persistently request information from the web (the so-called "polling" for new events), which is causing subsequent wakelocks.
In other cases, an update to a given app can also cause certain issues, which usually result in partial wakelocks. The latter keep your CPU constantly humming in the background, sometimes without your knowledge, and prevent your device from "going to sleep". That's a pretty substantial prerequisite for anomalous battery drain. Thus, it is advisable to regularly monitor the wakelocks on your device and see which of your apps go harsh on our system's resources.
Read more at:
What-are-wakelocks-how-they-affect-the-battery-life-of-your-Android-device-and-how-to-Greenify
Reference: https://developer.android.com/training/scheduling/wakelock.html
It is needed when you don't want CPU to sleep when user locks the screen for example.
If you have an IntentService without acquired WakeLock it will pause after a while if user locks the screen and it will continue its work when user wakes a device. With WakeLock acquired your service will work even if the screen is locked.
As #My God mentioned, it impacts on battery life a lot, so, use it only when you really need to finish some operation and you cannot wait till user wakes a device.
I would like to know if there is any way to turn off the screen on an android device on for example 19.00-22.00 every day. I have some tablets running in kiosk mode, and i want the screens to turn off when no one is using them and the store is closed.
Thanks
Screens will turn off automatically, if you have that set up properly in the device settings.
You can use AlarmManager and a WakeLock to arrange to keep the device screen awake during business hours. Have the AlarmManager start up a service that acquires the WakeLock and waits until closing time. You will need to use startForeground() in the service to prevent Android from killing off your service.
In the real world, this implementation would suck, as it forces you to keep a service running all the time -- if you let the service shut down, you lose the WakeLock and can never release() it, so the screen will never shut off. So, outside of this sort of kiosk thing, I do not recommend this technique.