Is it possible to determine the moment of switching of certain Activity from foreground to background and vice versa?
This activity should run in the separate process.
I need to write the application that collects some statistics from using of big set of applications (app names read from configuration file). My application works as Service and should remember moments of switching of activities between foreground and background.
Set of applications is sufficiently big and most part of these applications will never work on certain phone.
I don't know a lot about that but I think you could try to do some digging in that direction :
onFocusChangeListener
by applying it to the whole activity (refered as "this" in your onCreate for instance)
What about tracking intents? If you play around on a phone or emulator while looking at LogCat, you'll see that every time an activity is started or accessed there's a log message about the intent that was broadcast. I'm not sure how your program could intercept and process these, but it's another place to start looking.
Related
First sorry for my english.
I have a problem, and i can't find a solution, it sounds like:
i'm developping an app that's getting my location from gps and send it to a tcp server on pc , and store the data into a listview (for example). I have set a timer that send the location every 2 seconds. Everything works fine even if i connect two clients to server, until the phones gets locked .. then my server receive ugly string ..it seems like the sent-strings it straddles (the string contains parts of data from bought clients, parts are concatenated) .. but when i unlock the phones the server receive normal strings again..
I want to know how to make my app run in the same parameters when lock screen occurs .. Any ideas?
If you are doing this inside an activity or a fragment you are probably having an issue with the lifecycle of your app. If you want to understand the lifecycle, read this documentation article: http://developer.android.com/training/basics/activity-lifecycle/index.html
Doing nothing on your onPause method won't prevent your activity from sleeping, Android can kill your activity anytime.
The proper way to do this would be inside a Service, a service is a special component on Android that is executed independently of what the user is doing or not doing, and in this case, you could create a service that holds a wake lock in order to prevent it from sleeping for the couple of seconds you need to send your data.
An easier solution would be to use something like this Location polling library and suit it to your needs.
When the screen locks your activity is either paused on stopped and it is important you handle these methods so that any interuptions are handled elegantly and without error. Or so the app will continue to run in the background.
If you read up about the activity lifecycle.
During normal app use, the foreground activity is sometimes obstructed by other visual components that cause the activity to pause. For example, when a semi-transparent activity opens (such as one in the style of a dialog), the previous activity pauses. As long as the activity is still partially visible but currently not the activity in focus, it remains paused.
However, once the activity is fully-obstructed and not visible, it stops (which is discussed in the next lesson).
Activity Lifecycle from android.com
I'm new to Android development. I'v developed an android application which needs to store the connection/data even after 1 hour. Currently I have all the data and the connections(chromecast mediaplayer) in a singleton class. But, when the user puts the app into the background for about an hour, the activity is destroyed so the connections,data etc are lost causing my app to crash when re-launched.
I've read up on the android services, Can I use these services to hold the singletons so even when the activities are destroyed I can have data binded back to the views when re-launched?
Or is there a way to make sure that the activities are not destroyed when android decides to do a cleanup?
Please advise
Thanks.
I think you might misunderstand what an Android application is.
Your application is a bunch of components that run in a single Linux process. Components come and go, within that process. You have absolutely no control over the lifecycle of the process itself.
The answer to part of your question is that "yes" a Service will stick around after an invisible activity is destroyed.
When an Activity becomes invisible, it gets destroyed. If your process is not doing anything else, then the process is likely to be killed too.
If your process is also running a Service, it is less likely that it will be killed. It is just less likely, though. The process will eventually get killed. When it does, your singletons will be gone. There is nothing you can do to prevent that. So the answer to the second part of your question is "no". You cannot depend on singletons in your service to be around when the process is relaunched
You might look into using the Application object. Its lifecycle is roughly the same as that of your process. It will not live forever but it will be around whenever any other component of your application is around (except ContentProviders).
It sounds like you want to keep connectivity to a chromecast device around when your application is in the background. Obviously services can be helpful but I have a few comments that may come handy:
Services can be killed by system but based on how you have set them up (e.g. the return value of onStartCommand()), they can be restarted by the system. When that happens, you cannot expect that your dynamic data is still there (for example your singleton). You need to include logic to recreate what you need again (for example, rebuild your singleton)
Phone can go to sleep when left for a little while (or user can lock his/her phone), so when phone goes to sleep, wifi may drop after a little while, based on the phone settings and the build on your phone; some do this more aggressively and some not (even if you hold a lock, it can still happen). The point is that you have to assume that it may happen. Even if you have a service, your Cast connection will go down due to wifi loss, so the proper way to handle things is not to try to keep the connection up all the time (since you can't) but is to have logic to re-establish connection when circumstances is right. In order to do that, you need to preserve enough information to be able to bring things to the state that they were. Your logic should also be intelligent enough not to reconnect if it shouldn't.
Android O.S can destroy any activity , when it is low at resources it destroys any activities to make more space for other apps.
But you can use background service to hold your singleton
You can use this link to create your background service
I want to implement a service (or similar) on Android KitKat (4.4.2) in order to detect which is the foreground app and make something depending on which app it is "foregrounded".
I have read a lot of threads about determining which is the app is the foregound ON THAT MOMENT (https://stackoverflow.com/a/14044662/1683141). But I'm not able to see any thread about keeping this service continuosly monitoring in order to detect any changes on foreground. Kind of loop? Event registering?
For example, I want to be notified when LINE (messaging app) has or loses foreground. So I suppose the service has to be registered to some kind of event (I think Broadcast here is useless) in order to be notified and then take some action.
I don't know if that is possible. I hope it is.
Thank you for your help.
You are unable to keep your service alive if system decide to kill it. You are also unable to keep your service alive if your app is "unloaded" (whatever you mean), because your service is part of your app (and APK) and will be unloaded too.
I write application on android which will be runnig all the time on background. There will be only one starting view on first run. I want to user run instance of my app only once, and cant run any other instance at the time. When he try to run this app when one instance of this app is running already he sould see some warning notification. My problem is I dont know how to prevent user from multiple start of my app. Is this possible? If it is possible, how can I do it? Thanks for any help.
For background processing I would recommend to consider Services. Services are created to deal with longterm background tasks. I think foreground service(like Skype) may be interesting for you.
As Phil suggested you can you launch mode to control your activity behaviour. Consider using launchMode = "singleTop"
You need to pick a launchmode that will best fit your needs (probably singleInstance or singleTask). As for popping a notification, you can handle that in onCreate or onResume, however it doesn't have anything to do directly with how many instances are running.
Is there something in the Android developer guidelines that disuades developers from providing the option to "exit" (stop running) an application from within the application itself?
I love multitasking and all but it's not clear to me why:
the vast majority of apps don't have their own Exit functions and hence just keep running forever
don't give you a choice about running when you turn on the phone - they just do by default
Both of these things lead to memory usage constantly increasing and your device running with this performance burden all of the time despite the fact that you may only want certain apps to run some of the time.
Am I missing something?
Is there something in the Android
developer guidelines that disuadea
developers from providing the option
to "exit" (stop running) an
application from within the
application itself?
Yes. It is generally not needed, just as it is generally not needed to restart a Web server because some user with a browser decided (s)he is done with a Web app.
the vast majority of apps don't have
their own Exit functions and hence
just keep running forever
They don't keep running forever. Android will close things up as needed.
don't give you a choice about running
when you turn on the phone - they just
do by default
Those developers aren't paying attention to me.
Both of these things lead to memory
usage constantly increasing
Generally, it doesn't. If you find specific apps that do this, uninstall them.
and your device running with this
performance burden all of the time
Generally, it doesn't. If you find specific apps that do this, uninstall them.
Also, this question is a duplicate of this one.
"Both of these things lead to memory usage constantly increasing"
Which doesn't matter since Android apps are limited to a fixed amount of RAM. Freeing RAM won't give more RAM to other apps.
Essentially, there's no need for a quit button as long as the developer does a good job of designing their app. Android activities are stopped when they aren't visible and resources are needed elsewhere, so the are no longer consuming resources. You can read about the lifecycle here:
Here's a related question:
From Google's Android Application Fundamentals page:
Shutting down components
A content provider is active only while it's responding to a request from a ContentResolver. And a broadcast receiver is active only while it's responding to a broadcast message. So there's no need to explicitly shut down these components.
Activities, on the other hand, provide the user interface. They're in a long-running conversation with the user and may remain active, even when idle, as long as the conversation continues. Similarly, services may also remain running for a long time. So Android has methods to shut down activities and services in an orderly way:
An activity can be shut down by calling its finish() method. One activity can shut down another activity (one it started with startActivityForResult()) by calling finishActivity().
A service can be stopped by calling its stopSelf() method, or by calling Context.stopService().
Components might also be shut down by the system when they are no longer being used or when Android must reclaim memory for more active components. A later section, Component Lifecycles, discusses this possibility and its ramifications in more detail.
So it seems like Content Providers and Broadcast receivers should never be explicitly shut down, as they are inert while not handling their specific events.
As for Activities, I would argue in favor of having an end to it, but in certain cases. If your app has a finite state in which the user is done using it, why keep it alive until GC gets it? The activity manager still needs to keep track of that Activity while the user has finished their task. My best example for this is the Calculator. You open it, you have it solve a problem for you, and then you close it. If the onCreate function is so expensive that it's more effective to do onCreate once and then onRestart whenever the user moseys back to your application then you're probably doing something wrong. Maybe I'm misinterpreting how Android handles Activities, and if so I'm always interested in learning more :)
It all comes back to the answer that users want total control of their running and auto-start list and what they do and don't want installed, example: google maps, etc etc. there are no two ways about this.