When something asynchronous needs to be done it is often recommended to put this in a service, maybe an intent service. Great. However, it is also not recommended to startup an activity from a service ... So when asynchronous response comes back inside the service perhaps the user is on a different screen. Then their is the whole aspect of binding to services ... One is left wondering which way is better and why? I mean services are cool but there is the binding to service call and there is also the issue that services should not have callbacks into activities. So which way is better. What is the criteria for using an AsyncTask vs. a Service to do async work? Also there is requestForResult() option too ...
The criterias are basically,
Do you need to update some data regularly or continue some task (android gives an example of a music player where the music continues even when no activities are visible) even when your application activities no longer run? Use service here.
Do you have a need where your data or some task needs to be run by multiple applications? In such case the applications need to bind to your service and access the info.
Do you have a case there is IPC involved? Use a service.
Do you have a case where all u need to do is do a heavy task like downloading data, some kick ass algorithm which takes time? Do all heavy tasks in a background thread and update the UI once completed. use an AsyncTask.
Asynctask is simple. Used mostly in your activities to do heavy tasks in a separate thread to avoid ANR.
Services on the other hand is used to do tasks which needs to run even when your app is not running, other app needs to bind to update data, you need the updated data before displaying your activity.
I am sure there are more criterias, but these are just a few that just came to me.
Related
I have a very intensive task, where I parse around 100 json files stored in assets and create a tree structure from that..
Then i update the UI based on resulted tree.l
Currently, I am using AsyncTask to do this job.
But, I am looking for better, efficient and clean way to do this. Any libraries or any other in-built functionality which i should use ?
I would go with an IntentService here. It already provides a background thread and it will stop itself once it's done. If you need to update the UI after that, you can use a Handler or a BroadcastReceiver.
EDIT
You can still use an AsyncTask but still, start it from a Service. AsyncTask is just a wrapper around java thread, it's not an Android component. You have to start it from some context, in this case it's either Activity or Service.
If you start it from Activity then your long-running operation will depend on the UI which in most cases will cause a memory leak. Service is a background component which runs independently from the UI. Also, Service will increase your app's process priority so that it less likely to be killed by Android when the system is running on low memory.
If you use IntentService, you don't need an AsyncTask anymore, it runs on the backround thread already. If you want to go with a regular Service, you will need to implement background execution on your own. Via java thread or async task for example.
If this is heavy and long running use a Service and communicate using broadcast receivers.
My application does a sync process every 30 seconds.
What I do is, send some data, and accordingly get a set of data, and update/insert into my local sqlite DB. Sometimes, I updated my GUI as a result of these operations.
I read in several posts that an asynctask can do this task perfectly, and in some other posts many people discouraged the use of asynctask, and told me to implement the intentService/broadcast receiver approach.
Which one is better? and when ?
There are multiple considerations that you must weigh in order to best decide how to approach your situation. Acording to the doc:
...an activity that initiates a long-running
operation might do well to start a service for that operation, rather
than simply spawn a thread — particularly if the operation will likely
outlast the activity. Examples of this are playing music in the
background and uploading a picture taken by the camera to a web site.
Using a service guarantees that the operation will have at least
"service process" priority, regardless of what happens to the
activity.
A Service is a part of your Application that has no UI. It may be called by a UI(Activity) to be started, or may be started by any other component of your Application. When developing, you have the freedom to place it on a different thread, or even run it in a different Task or Process. This allows you to ultimately separate it from your UI. Additionally, you may start the Service to run independently (startService) or bind your activity to it (bindService) depending upon your needs. By using custom Handlers, you can set callbacks to update the UI with your progress. A Service does not necessarily end if a User changes Activities, but may be ended at ANY time by the OS.
A AsyncTask is always instantiated from the UI thread. It only allows specific callbacks, but simplifies the process of multi-threading for the purposes of relatively short transactions (as compared to dedicated separate threaded services) that are inherently tied to actions performed by an Activity. Whenever a User changes Activities, the AsyncTask is put on "pause" and may even die because there is no UI thread for your Activity any longer.
The problem with the AsyncTask is if the user goes to another Activity you can't transfer that object to the other Activity so it dies. There are tricks you can play when say the user rotates the screen or something like that, but that doesn't extend to general purpose destruction. AsyncTask can randomly die. On the other hand you can definitely communicate between Service and Activity, but it's tricky to do it right.
So, depending on your scenario, you have to take a design decision.
If you need to update the UI then AsyncTask will be a better fit, however if you need it to update in the background when the app is not running then IntentService would be better and you will need to come up with a way to update the UI from your IntentService
This is more of an opinion based question so I would not expect one definite answer. Its a per-app basis question
I just read Android Architecture Tutorial: Developing an App with a Background Service (using IPC). It is basically
Have a service run in separate process.
A repeated timer event will occur in the service.
Within the timer event handler, it will perform networking to retrieve tweet, and inform all the listener attached to it. Listeners are attached to it through IPC.
I can see there are 2 major characteristics with this approach.
Tweet retrieving action run within separate process.
It always run, even the main activity has quit.
However, if "It always run" is not my requirement. I want everything to stop when I quit my main Activity.
Will it be better, if I use AsyncTask (Or Timer) within my main Activity, to perform tweet retrieving action? Everything will be run within single process. No more using Service.
Using AsyncTask (Or Timer), seems simpler. We no longer need to deal with IPC.
Or, using Service approach might be better? Am I missing some goodies provided by Service?
Using service is a better approach as it will allow you to perform the polling independent from the application flow.
As it is a task where no user interaction is required and it has to be done in the background without disturbing the main UI of application and whatever the user is doing, a service is an ideal candidate for its implementation.
It is possible to bind the service with the application in such a way that when the main application terminates, it will also turn off the service.
I would take the view that a TimerTask can be set to execute and repeat at a given interval, Timers run on a separate thread so all this work would occur in the background without disturbing the UI. It would be easy for you to trigger an update within your app when the TimerTask completes and update the UI when you want.
When you exit the app it's a simple case of calling cancel() on your Timer and the purging all the tasks with purge().
Nice and easy and you don't need to implement IPC, which can be very fiddly to get right.
EDIT
Using AsyncTask you can do pretty much exactly the same thing but you'll have to manually schedule the next run. I have used both solutions in the past and found them to work equally well so it's all down to your preference.
At first you have to know, that a service isn't a Thread. If a activity binds a Service and runs as a Deamon, but a ASynchTask is another thread.
ASynchTask's are designed for doing some work which should not running on UI-Thread (for example processing some larger calculations)
Services are designed to run permanantly on Background.
If you want to permanantly check for new tweets, even if your activity is stopped or paused, you should use a Service, which checks into an own thread for new data.
TimerTask are good old java style implementations which run on their own thread.
You can used them for processing some data, but you'll have some problems to manipulation UI. If you want to be it on propper "AndroidWay", use a Handler instead of TimerTask.
First of all, I know the tutorial you are following...I've followed that tutorial myself while trying to learn IPC. One thing you need to know is, The Android docs explicitly say,
Note: Using AIDL is necessary only if you allow clients from different applications to access your service for IPC and want to handle multithreading in your service.
If at all possible, you should just bind to the service.
Also, you must consider, do you really need a service? Consider that the Android Twitter app doesn't even refresh tweets for you, its on an as needed basis. Polling can be battery intensive, so you must consider if this is really necessary.
Also, will you be using these tweets from multiple activities? If so it would be nice to not duplicate the code in multiple places. So maybe you do want a service in this case.
Other than that, I would recommend that you start simple (Async task with a timer to update it), and move to a service if you think you need it.
Why do I read in the answer to most questions here a lot about AsyncTask and Loaders but nothing about Services? Are Services just not known very well or are they deprecated or have some bad attributes or something? What are the differences?
(By the way, I know that there are other threads about it, but none really states clear differences that help a developer to easily decide if he is better off using the one or the other for an actual problem.)
In some cases it is possible to accomplish the same task with either an AsyncTask or a Service however usually one is better suited to a task than the other.
AsyncTasks are designed for once-off time-consuming tasks that cannot be run of the UI thread. A common example is fetching/processing data when a button is pressed.
Services are designed to be continually running in the background. In the example above of fetching data when a button is pressed, you could start a service, let it fetch the data, and then stop it, but this is inefficient. It is far faster to use an AsyncTask that will run once, return the data, and be done.
If you need to be continually doing something in the background, though, a Service is your best bet. Examples of this include playing music, continually checking for new data, etc.
Also, as Sherif already said, services do not necessarily run off of the UI thread.
For the most part, Services are for when you want to run code even when your application's Activity isn't open. AsyncTasks are designed to make executing code off of the UI thread incredibly simple.
Services are completely different: Services are not threads!
Your Activity binds to a service and the service contains some functions that when called, blocks the calling thread. Your service might be used to change temperature from Celsius to Degrees. Any activity that binds can get this service.
However AsyncTask is a Thread that does some work in the background and at the same time has the ability to report results back to the calling thread.
Just a thought: A service may have a AsyncTask object!
Service is one of the components of the Android framework, which does not require UI to execute, which mean even when the app is not actively used by the user, you can perform some operation with service. That doesn't mean service will run in a separate thread, but it runs in main thread and operation can be performed in a separate thread when needed.
Examples usages are playing music in background, syncing data with server in backgroud without user interaction etc
AsyncTask on other hand is used for UI blocking tasks to be performed on a separate thread. It is same like creating a new thread and doing the task when all the tasks of creating and maintaining the threads and send back result to main thread are taken care by the AsyncTask
Example usage are fetching data from server, CRUD operations on content resolver etc
Service and asynctasks are almost doing the same thing,almost.using service or a asynctask depends on what is your requirement is.
as a example if you want to load data to a listview from a server after hitting some button or changing screen you better go with a asynctask.it runs parallel with main ui thread (runs in background).for run asynctack activity or your app should on main UI thread.after exit from the app there is no asynctask.
But services are not like that, once you start a service it can run after you exit from the app, unless you are stop the service.like i said it depends on your requirement.if you want to keep checking data receiving or check network state continuously you better go with service.
happy coding.
In few cases, you can achieve same functionality using both. Unlike Async Task, service has it's own life cycle and inherits Context (Service is more robust than an Async Task). Service can run even if you have exited the app. If you want to do something even after app closing and also need the context variable, you will go for Service.
Example: If you want to play a music and you don't want to pause if user leaves the app, you will definitely go for Service.
Comparison of a local, in-process, base class Service✱ to an AsyncTask:
✱ (This answer does not address exported services, or any service that runs in a process different from that of the client, since the expected use cases differ substantially from those of an AsyncTask. Also, in the interest of brevity, the nature of certain specialized Service subclasses (e.g., IntentService, JobService) will be ignored here.)
Process Lifetime
A Service represents, to the OS, "an application's desire to perform a longer-running operation while not interacting with the user" [ref].
While you have a Service running, Android understands that you don't want your process to be killed. This is also true whenever you have an Activity onscreen, and it is especially true when you are running a foreground service. (When all your application components go away, Android thinks, "Oh, now is a good time to kill this app, so I can free up resources".)
Also, depending on the last return value from Service.onCreate(), Android can attempt to "revive" apps/services that were killed due to resource pressure [ref].
AsyncTasks don't do any of that. It doesn't matter how many background threads you have running, or how hard they are working: Android will not keep your app alive just because your app is using the CPU. It has to have some way of knowing that your app still has work to do; that's why Services are registered with the OS, and AsyncTasks aren't.
Multithreading
AsyncTasks are all about creating a background thread on which to do work, and then presenting the result of that work to the UI thread in a threadsafe manner.
Each new AsyncTask execution generally results in more concurrency (more threads), subject to the limitations of the AsyncTasks's thread-pool [ref].
Service methods, on the other hand, are always invoked on the UI thread [ref]. This applies to onCreate(), onStartCommand(), onDestroy(), onServiceConnected(), etc. So, in some sense, Services don't "run" in the background. Once they start up (onCreate()), they just kinda "sit" there -- until it's time to clean up, execute an onStartCommand(), etc.
In other words, adding additional Services does not result in more concurrency. Service methods are not a good place to do large amounts of work, because they run on the UI thread.
Of course, you can extend Service, add your own methods, and call them from any thread you want. But if you do that, the responsibility for thread safety lies with you -- not the framework.
If you want to add a background thread (or some other sort of worker) to your Service, you are free to do so. You could start a background thread/AsyncTask in Service.onCreate(), for example. But not all use cases require this. For example:
You may wish to keep a Service running so you can continue getting location updates in the "background" (meaning, without necessarily having any Activities onscreen).
Or, you may want to keep your app alive just so you can keep an "implicit" BroadcastReceiver registered on a long-term basis (after API 26, you can't always do this via the manifest, so you have to register at runtime instead [ref]).
Neither of these use cases require a great deal of CPU activity; they just require that the app not be killed.
As Workers
Services are not task-oriented. They are not set up to "perform a task" and "deliver a result", like AsyncTasks are. Services do not solve any thread-safety problems (notwithstanding the fact that all methods execute on a single thread). AsyncTasks, on the other hand, handle that complexity for you.
Note that AsyncTask is slated for deprecation. But that doesn't mean your should replace your AsyncTasks with Services! (If you have learned anything from this answer, that much should be clear.)
TL;DR
Services are mostly there to "exist". They are like an off-screen Activity, providing a reason for the app to stay alive, while other components take care of doing the "work". AsyncTasks do "work", but they will not, in and of themselves, keep a process alive.
I am developing an android app which fetches/uploads data from/to the web service every n minutes. This upload/download is only done when the app is running. But this might change in future.
I dont update the UI when the new data is downloaded. The UI is only updated if the user is on the current screen(app have multiple activities)
My question is what is the best approach to this problem.
I dont think service is the right approach as it sounds like an overkill(in the present scenario). AlarmManager could be an option.
Running threads inside a service be an option ..something like this .
Any pointers/suggestions would be great.
Thanks
I am using AsyncTask in my activity to ask .net web service some information and it works and easy to use.
AsyncTask enables proper and easy use of the UI thread. This class allows to perform background operations and publish results on the UI thread without having to manipulate threads and/or handlers.
Well, in this case, since the app would already be running during the time, either would work great, but a service can be called from anywhere within the application so this is where I would use the service over the thread.
If you want to create the thread to only be used in lets say Main.java, then thread would work fine, these are the only things that I can see really making ANY difference at all, they're really pretty close, and in this case neither gives a distinct "correct" answer, but I would choose Service
I think all approaches you noted would work ok. Personally I'd go with this:
Use AlarmManager to wake download service. Start it when Activity is shown, stop it when activity hidden.
Download service should be short lived: start it to do the upload/download and then shut it down.
If download service does get some new data, it sends a Broadcast which Activity listens to.
Just broadcast a message after your upload/download is done, and then have a receiver start the service and then have that service stop itself. And you are done.
This should be done if you dont plan on polling the server for new information or anything. Primarily this kind of approach would be for onetime update, interpret, finish. And wait until the next update. Which primarily for most cases is streaming.. but depends on what you are getting.