I'm new to Android development, so I might be missing something obvious. I want to launch an Activity when the user's phone clock hits a specified time (similar to an alarm). However, I'm not sure how I would go about doing this as constant polling of the clock seems inefficient and a waste of resources. Do I need to capture broadcast events from the clock, or use PendingIntents? If someone could point out some SDK methods/services I should read about, it would be much appreciated.
Thanks.
Take a look at the docs for android.app.AlarmManager.
This class allows your application to schedule PendingIntents for broadcast at specific times, which sounds like exactly what you're looking for. Just schedule a PendingIntent that launches the desired application.
Be aware that when your alarm fires, the phone will be prevented from sleeping until (and only until) onReceive() finishes executing. If you need to keep the phone awake longer, you may need to implement your own wake lock.
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I want my app to monitor every percent change and be able to execute some code when it changes even when the screen is off.
Yes, I know this is a bad idea and will drain battery unnecessarily. I am giving the user the option to turn this off. Also, this is more of an experiment at this point than a user-friendly feature. So please do not answer that I should not monitor every change.
I also know this is possible because Tasker implements this quite well. You can set a profile to do something on "Battery Changed" and it works when the screen is off. How is Tasker doing this?
From my research I have found that I will probably need to use AlarmManager and a partial wake lock from the PowerManager class. However I don't know how to best use these classes. Should I set an alarm manager to check every minute for a change? Tasker seems to not eat up too much battery when doing this so I would like to keep that in mind.
I have this working when the screen is on just fine. I have a service that registers an ACTION_BATTERY_CHANGED intent filter and a receiver to implement my code that I want to run. However when the screen is off, the code does not run until I "wake" the device by turning on the screen.
How is Tasker doing this?
You would have to ask the developers of Tasker.
Should I set an alarm manager to check every minute for a change?
It would not need to be nearly that frequent. You can only get battery charge levels in integer percentages, at best. Checking every 5-10 minutes is probably more than sufficient. You could also consider:
Letting users control the polling frequency
Implementing a learning algorithm that tries to determine a good polling interval based upon how the device has behaved previously
I have a service that registers an ACTION_BATTERY_CHANGED intent filter and a receiver to implement my code that I want to run.
Yuck. There is no added value for you tying up memory waiting for the battery level to tick over.
You can get the current battery level by calling registerReceiver() with an IntentFilter for ACTION_BATTERY_CHANGED and a null BroadcastReceiver. registerReceiver() will return the last ACTION_BATTERY_CHANGED broadcast that went out. Hence, again, a polling mechanism should be just fine.
I want to build an alarm application. I've seen some examples and some of them use Service and some use BroadcasterReceiver. The user will set the alarm and then when it goes off they'll have to do certain things like solve a mathematical equation or scan NFC tag before it turns off. Which one should I use?
If you are using AlarmManager with a _WAKEUP alarm, you must have the PendingIntent route to a BroadcastReceiver. The only thing Android guarantees with a _WAKEUP alarm is if you use a BroadcastReceiver, Android will keep the device awake long enough for onReceive() to complete. Anything else, all bets are off.
It the work you want to do would take more than a couple of milliseconds, have the BroadcastReceiver turn around and pass control to a service, which can do its work on a background thread. You may wish to use my WakefulIntentService for that; if not, you will need to manage your own WakeLock to ensure that the device stays awake until the service can complete its work.
I'm have a widget that is being updated from a service. When the user then turn off the screen, the service stops and won't start to update the widget again when the user wake up the device. So on to my question, is there some way to "restart" the service when the user wake up the device? I know I can keep the service keep going when the screen is locked, but I think it would drain to much battery then... I have google'd alot but haven't found anything...
Thanks in advance!
EDIT: Okey, this is strange! Now somehow it does that automatically, so it's working now! Thanks anyway!
EDIT 2: Or, now I don't really think it's the screen lock that stops the service, cause it just sometimes stops randomly without crashdialog when I use the phone... Anyone know how I should do to fix that?
For a widget it usually doesn't make sense to keep a service running all the time, you usually update the widget periodically.
The easiest way to do this and to be battery efficient is to schedule an intent using AlarmManager and setAlarmInexactRepeating:
Schedule a repeating alarm that has inexact trigger time requirements; for example, an alarm that repeats every hour, but not necessarily at the top of every hour. These alarms are more power-efficient than the strict recurrences supplied by setRepeating(int, long, long, PendingIntent), since the system can adjust alarms' phase to cause them to fire simultaneously, avoiding waking the device from sleep more than necessary.
The intent should trigger a BroadcastReceiver which in turn should trigger your service to update the widget. Using IntentService is usually a good choice for that.
If you need more control over the intent scheduling, you can also set the alarms yourself in when the service is finished with updating the widget, and supply RTC or ELAPSED_REALTIME as the type of alarms. Both types won't wake up the device if it's sleeping. If the device is not sleeping (but locked) you'll effectively piggy back on other events that woke the device.
If you really need to update as soon as the device is unlocked, the ACTION_USER_PRESENT broadcast might be what you need, but I'd still recommend to implement that as an addition to scheduling a periodic update.
Yes this is Possible!
When the user turn off the screen You Have to handle BroadCast Receiver (http://developer.android.com/reference/android/content/BroadcastReceiver.html)
That handle to Stop service & the service stops and stop to update the widget,
when the user wake up the device you have to Receive Broadcast start to update the widget.
I think it would be The best idea to save more battery.
For More information Please Refer this Link
In my app, I have to make it vibrate in time intervals defined by the user.
Basically it has a chronometer that makes the device vibrate when it has reached the defined time. Currently I do that by reading the chronometer value and comparing it with the desired value, in the onChronometerTick() method
I need this app to work in the background too. I've googled and found some examples about the android Service class.
My doubt is how my Service class will get the chronometer value? I've seen that the Service class can't handle layout components.
How can I do this? Is service the best way to handle this issue?
Thank you!
It sounds like what you want is an alarmmanager. Here's what it says regarding alarm managers:
These allow you to schedule your application to be run at some point
in the future. When an alarm goes off, the Intent that had been
registered for it is broadcast by the system, automatically starting
the target application if it is not already running. Registered alarms
are retained while the device is asleep (and can optionally wake the
device up if they go off during that time), but will be cleared if it
is turned off and rebooted.
So if you're going to want the counter to continue after turning it off, you'll have to find an on-boot option or something. But yes, this is what you need to schedule events if you want them to keep happening after the screen locks.
I'm looking for some timer alternative, since timer dies with app, is limited, and every timer launches own thread.
Sometimes I need to launch about 20-30 timers.
I need to set some event, in time, and when it comes display app screen. Is it possible?
This may or may not be possible depending upon your definition of "dies with app".
You can use AlarmManager to schedule PendingIntents to be invoked at specific times in the future. Those PendingIntents can launch activities. This will work if your app "dies" from ordinary causes.
However:
If the user force-closes your app via Settings, your alarms are unscheduled, and there is nothing you can do to stop this (nor do you have any alternative to AlarmManager that somehow survives this)
Please allow the user to determine whether or not you display an activity or raise a Notification at these times, as users may not necessarily appreciate having their game, navigation, video, or phone call interrupted by your activity.
You should use AlarmManager.
As CommonsWare says that there are some limitation of it, but that is ok, if an user force closes your application it means he doesn't want to use your application (any more or due to sort of memory)....
And I have a solution (but may be not the best), because you can not listen if user force closes your app, so one way is that you can re schedule your event on each start of your application. I know this is not a good solution but ..... we have no any other way yet
Here is a good example.