Ive created an app which needs to run an intent service while the application is closed if two values are out of sync(eg. 2 of 3). The intent service updates a text view within my application which will display the two values using a BroadcastReceiver.
Also the intent service is created in one activity but should be stopped in another. The two values are based on a GPS location update and that location being sent through a web service method. At points the GPS may update location and the web service might not due to limited connectivity to mobile data/wifi therefore leaving the values out of balance(1 of 3) and if the user closes the app this needs to continuously run until the value reaches 3 of 3(the GPS stops updating when app is closed).
The intent should run until the values are in sync again even if application has been closed. How would i keep this running whilst the app is closed and then stop it when the the values are in sync
Because an IntentService is like a Thread. It's designed to run aslong as it takes to finish onHandleIntent().
Use a regular Service and control it with stopService or stopself() if you want to manage the lifecycle.
edit: by the way, why do you mix asynctask and intentservices at all? Use one of them but dont mix it. AsyncTask handles all. Background Threading and processing in the mainUI. Anyway, for using GPS you should decide to use a regular Service and (maybe) create a Thread within the Services onStartCommand().
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So basically what i am trying to do is i want a service that runs in background and updates the LatLong to the server. This operation needs to happen all the time even if the application is running or not.
Now when the application is launched i want the service to calculate the distance between the latlong and update the UI in addition to the work that it was already doing i.e. updating the latlong to the server. i want the service to do the additional work for multiple activities. lets say i launch the application and i am on Activity A, onclick of a button on Activity A the service starts updating the UI and when we click gain it stops updating. Now i am on Activity B and on click i want the service to do some work in addition to the updation of LatLong and update the UI.
What would be the best approach to achieve this.??
EDIT
The problem i am facing is not getting the service update the UI but making the activity communicate with the service when it has already started.
i can pass on some data when i am starting the service but how to communicate with the service when it has already started. How to tell the service that see you are already running and doing some operations now you have to perform some more operation on top of the previous operation.
I can make some static method in the service and call them when i need to perform the extra operation but i dont wanna do that.. i want to better approach.
Here is the basically services runs on the same main thread process as ui. When you want make it run continuously you have run it in your tread. In this way you avoid service being get stopped as application go in background or killed. (Please take look at Service.START_STICKY flag, this is what you need as i guess).
And more coming your second problem of activity getting updated with service information or data that is being collected for this you need look at " How Bind the service". (In activity check for service connection and Binding to a activity, Unbindibg is also there have look at it also). Activity has all the call backs for it you need to implement binder.
EDIT
Service to update ui has to have send and receive intent mechanism. You can broadcast and intent from the services check your activity is running or not. If running broadcast intent and have receiver in activity to listen it.
You can do it by interface mechanism too
I have been going through this very short tutorialand I am confused as to what is the function of the service. I am also confused as to what is the function of the broadcast receiver.
I tried to do some research and here is what i understand:
- services run in the background, but... i don't understand why we need something
to run in the background to make the phone wake up at a certain time.
I "think" the broadcast receiver acts as some kind of catcher's mit, in that
when the pending intent is launched at a specific time, it catches it then
launches the service... how close am I to the truth ?
As i think that services are used for long running tasks and especially in those cases that run when your main activity is not running.
For this functionality we can use threads this make us to say that a thread is created inside our activity and it can't be active outside of the our main activity,
that is the drawback that's why we have services .
Document URL
Services can be used to run long running tasks independent of your screen flow. For example, consider your application require to communicate with a server via socket throughout its running duration, you can start a service to handle this. Imagine that against starting the socket and making connection at the start of every activity, and clean up when that activity stops.
Services by default run in the main thread. But you can start separate threads in a service context, just like you do in an Activity. If your background task can overlap across multiple activities, then it is better to start it in a Service context because every Thread/AsyncTask created retains the context that it is running. In that case your Activity will be retained even if user navigates to another activity because a thread started from that Activity is already running. If Activity is retained, it might prevent all its views, images getting garbage collected.
What Services can't do is to directly alter UI components. For that it needs to communicate with the currently running Activity context. In short, if your non UI task does overlap the life time of a particular Activity, it is better to shift that task to a Service.
What is the function of the service ?
A service is a component which runs in the background without direct interaction with the user.
As the service has no user interface, it is not bound to the lifecycle of an activity.
Services are used for repetitive and potentially long running operations, i.e., Internet downloads, checking for new data, data processing, updating content providers and the like.
TO READ: Service
What is the function of the broadcast receiver ?
Broadcast receivers are the second kind of component. Like services, they only exist in the background and don't interact with you directly. But unlike services, they can't stay running or perform long tasks: they exist to respond to events. And unlike activities and services, more than one broadcast receiver can be started in one go.
Each broadcast receiver can react straight away, for example by creating a notification, or it can start a service or an activity to take further action. As soon as the broadcast receiver has handled the event, it is stopped and will not run again until another similar event is broadcast.
TO READ: BroadcastReceiver
I don't understand why we need something to run in the background to
make the phone wake up at a certain time ?
We don't want that the application should necessarily be in the foreground to wake the phone up.
Moreover we want notifications in the background.
We started the service. Now even if we close the application, you can get the phone wake up notification. This is so useful.
Services are great to interact with a user through notifications (a way of alerting a user about an event that he needs to be informed about or even take some action on getting that information). Many a time, applications will need to run processes for a long time without any intervention from the user, or very rare interventions. These background processes need to keep running even when the phone is being used for other activities / tasks.
To accommodate for such a requirement, android has introduced the "Service" component.
It runs in the background until it stops itself. This means that a service could be keeping your phone awake (using a wake lock), running down the battery, or using lots of network data, without anything showing on the screen.
I "think" the broadcast receiver acts as some kind of catcher's mit,
in that when the pending intent is launched at a specific time, it
catches it then launches the service... how close am I to the truth ?
Correct, they are meant to respond to an intent (usually one sent by a service or a system event), do something, and be done. When an intent is broadcast via sendBroadcast, it will be sent to all receivers that have matching intent filters.
Service - is a component of android, which runs in the background with out any UI. By default service will run in Main thread only.
Thread - is not android component, but still one can use thread to do some background task. Using thread in place of service is discouraged
I started learning android i've been playing with it and so far so good but i have some doubts about Services, i started learning them today so by gently if a say something very wrong.
For example, i want my app to grab some information over the internet from time to time, this polling period is defined by the user, then the UI gets updated. I though about creating a Service that run lets says every 30 minutes, gets the information and updates the UI.
If i get it right:
An IntentService just executes an operation and stops by itself sending the result through an intent(right?), so i think it's not what i want.
A Bounded Service is most likely used when you want IPC or allow binding from external apps, which again i think it's not what i want.
I think a Local Service is probably what i need, using a LocalBroadcastReceiver to update the UI, how can i make it to run the operation every X minutes( Handler postDelayed, ScheduledExecutorService or Alarm Manager ? )
If i understand it right a Service if not bounded can run infinitely if it's not killed due to low memory problems, making it a foreground Service is the safest ?
Last thing and it's kind of a noob doubt, if the user leaves the application(Click Home Button or opens other app) the app is still in background but the activities are in "Paused" or "Stopped" mode will the Service still be able to talk to them ?
Sorry for long post and thank you.
Your requirement : after every x minutes, start a service, pull some date, update UI.
Solution :
Define or set an alarm for every x minutes, to trigger a receiver.
From receiver start the service.
In the service, start an async task to fetch the data in doInBackGround().
Once data is fetched, from onPostExecute() send a broadcast to your activity.
In the activity have a dynamic receiver registered for broadcast sent from service.
From dynamic broadcast receiver update UI.
From what you've explained I wouldn't personally use a service.
The Android docs on services explain more but here is a snippet:
http://developer.android.com/guide/components/services.html
A Service is an application component that can perform long-running operations in the background and does not provide a user interface.
You could perhaps looks at using an AsyncTask, especially given that you only want it to run whilst the app is running:
http://developer.android.com/reference/android/os/AsyncTask.html
This class allows to perform background operations and publish results on the UI thread without having to manipulate threads and/or handlers.
There is a good answer here on how to run an AsyncTask repeatedly at specific time intervals: How to execute Async task repeatedly after fixed time intervals
I'm in little bit confusion where in what case I need to use application components like Service, asyncTask and Broadcast Receiver.
Can any one explain what the exact difference between these there and where I need to use these components?
AsyncTask is a friendly way to create a new thread that performs some work asynchronusly.
A Broadcast Receiver is something like an Event Handler for system events. It can run in
background and perform an action when something happens, like turning the phone off or turning wifi on..
A Service is just an app that works in background (like a daemon) and serves information to an app or just performs tasks.
Sorry for my English, I try to let me understand but it is not my mother tongue
I will get straight to where I have applied these three in my projects so far:
1.Service:Something you want to perform in the background without any user interaction.For instance fetching location data continuously or sending some data continuously to your server.You can also use services to perform tasks every few time units.For example sending ten minute background updates.
2.AsyncTask:Making a new thread of execution.Best use I have encountered so far is calling a web service..I did the following using an AsyncTask for web service calls
1.Display Progress bar in onPreExecute()
2.Perform my web service calls in doInBackground(Params...)
3.In onPostExecute(Result) update the UI or do some other stuff with the response from the web service.
3.BroadCastRecievers are like global recievers for your app.They can listen for both System events like a phone restart or a custom event within your app.I used them for starting a service when the phone was restarted,which stopped when we switched off the phone.
Let me explain with a usecase, so you understand it better -
AsyncTask - Want to get something from the server, or post something to the server? If we do so on the main thread, the user won't be able to interact with the app. So Asynctask is used, and it performs the network activity in a different thread.
Service - Want to manage something in the background? Like get the users' location every 10 minutes or 1 hour, or alert the user when he is crossing a particular area based on the location. The Service makes the app run even when the app is not opened (the user might be doing something else, or the phone is locked, the Service still runs in the background).
Broadcast Receiver - Assume, you are tracking location and storing locally (when the internet is down). Not when the internet is up, you want to send all of them. So you register with the OS, that you want to listen for that specific event, and you get control.
Or when you want the server to know that the device is restarted, then we just have to implement it.
Clear?
A service and its local memory-variables are loaded into memory and is always running
A BroadCast receiver is only garanteed to be in memory and running while processing an event.
A Broadcastreceiver can be removed from memory by the operating system if the memory is low.
"Service" is a component which runs in the background, without interacting with the user. Every developer can create new Services in his application. Services support true multitasking for Android, as they can run in their own process.
"AsyncTask" encapsulates the creation of Threads and Handlers. An AsyncTask is started via the execute() method.the execute() method calls the doInBackground() and the onPostExecute() method.
Mostly main purpose to download something without user interaction.
"Broadcast receiver" is a class which extends BroadcastReceiver and which is registered as a receiver in an Android Application via the AndroidManifest.xml file(or via code).you can register a BroadcastReceiver dynamically via the Context.registerReceiver() method.
The class BroadcastReceiver defines the onReceive() method. Only during this method your BroadcastReceiver object will be valid, afterwards the Android system can recycle the
BroadcastReceiver.
I start an activity in my class Locator.java which starts a locacionListener Service. That activity writes positions to a database. I wonder if when i move to next screens(activities), positions will keep writing to the database, or I would need to go back to Locator.java to keep writting. The same when I minimize the application.
I have thouhgt about using a Service, but I want to be sure I need it.
As long as the service is started, and providing sufficient resources are available on the device, the service will continue to run in the background. Switching activities, minimizing or closing the app doesn't change that. It's up to you to formally stop the service.
The business logic for capturing location updates and storing them in the database should be implemented in the service however, and not in the activity. (The activity can be used to control the state of the service (stop-start), and to display data from the database, but the bulk of your location update / storing in database logic should be triggered from the service.
You can check the running services on your android device (Settings - Applications - Running Services). You should see your service, and the amount of time it has been running.
Depending on your requirements, a simple service will not cut it. If you for example you also want to capture location updates and store them in a database while the device is sleeping, you'll need to look at WakefullintentService