I'm creating an application that connects to an XMPP server on Android. I want to keep the connection on till the user logs out.
Should I use a regular Service or a Bound Service to keep the connection on?
Any tips, advice and helpful information are welcomed.
I like this explanation:
Started services are easy to program for simple one way interactions
from an activity to a service, however, they require more complex and
ad hoc programming for extended two-way conversations with their
clients.
In contrast, bound services may be a better choice for more
complex two-way interactions between activities and services. For
example, they support two-way conversations.
So, as you said, If you want to interact with the service use bound service. With started services (or intent services) you could do it, only it would require more complex programming.
(by Douglas Schmidt: https://www.youtube.com/watch?v=cRFw7xaZ_Mg (11'10'')):
Here is a summary that helped me understand (thanks Doug):
Finally, one last link that helped me also:
http://www.techotopia.com/index.php/An_Overview_of_Android_Started_and_Bound_Services
Started services are launched by other application components (such as an activity or even a broadcast receiver) and potentially run indefinitely in the background until the service is stopped, or is destroyed by the Android runtime system in order to free up resources. A service will continue to run if the application that started it is no longer in the foreground, and even in the event that the component that originally started the service is destroyed
A bound service is similar to a started service with the exception that a started service does not generally return results or permit interaction with the component that launched it. A bound service, on the other hand, allows the launching component to interact with, and receive results from, the service.
A bound service is the server in a client-server interface. A bound service allows components (such as activities) to bind to the service, send requests, receive responses, and even perform interprocess communication (IPC). A bound service typically lives only while it serves another application component and does not run in the background indefinitely.
If all the code exists in one activity from user connected to user logout then go for bound service
But if it is code exists in multiple activities try with service
I found out the difference between the two and when to use it. If you want to interact with the service (for example send arguments etc), use bound service and it return the service object in the onServiceConnected method (where you can call methods in the service). You cannot interact with a regular service (from another class)
Related
I have a service, I need to communicate to with it (one service - many fragments/activities). There are two options for this:
Have a singleton that controls the service - starts it and then binds to it (using the app context)
Have a singleton that controls the service - starts it, the service when ready registers back as a delegate to the singleton (in a WeakReference)
Solution no 2 seems simpler to me, but whenever I read about communication with services there is the concept of the bound service.
Is there any benefit of having a bound service instead of the service registering itself as a delegate (and unregistering with onDestroy)?
Edit 1: The service is to keep the communication alive, it's expensive to set up a new communication channel. Even if no one requested any data it should keep the channel alive (heartbeat).
The service is foreground, it should run even if the activity that requested the data gets killed by the system. The next time it is created the data will be there.
The data requested by one screen might be useful for some other (therefore has to be stored in a singleton).
Bound and unbound services are both usable patterns and you should pick whatever pattern is better for you use case.
You should pick bound service if you want your service to have the same lifecycle as the components that bind to it. If you need an independent service use an unbound version.
The only benefit of one approach versus another is the simplicity of implementation.
In you case, I think you need the service only while there are running activities and fragments, then the easiest way, in my opinion, would be to make a bound service and make every activity bind to it. With that, you'll get a simple communication interface between you activities (and fragments, since they have access to containing activity) and your service.
The benefits of this approach are:
the service will stop itself if all activities unbind and start itself when first activity binds to it.
you won't need to track all running activities in the singleton and manually unbind
you won't need to maintain a singleton manager, less code -> less bugs
sometimes onDestroy can be skipped by the system and you can leak the service with the 2 approach.
Since you need your service to be running the correct option will be to use a started service and make each activity bind to it when needed. It's a common pattern.
Started service will run until you explicitly stop it or it stops itself, you can have a singleton manager that will be responsible for that.
But at the same time you can communicate with the service from your activity using binding.
So basically comparing with the first suggested approach, you'll need some instance that will start and stop the service, but the communication between activities and service will be the same - using binding.
Yes, using a bound service in Android is a much better option when communicating with Views like Activities/Fragments. This is because of the following reasons,
It runs synchronously.
You can have more control on the service data when to show on UI thread of the view. You can choose when to call it in async/sync way.
LocalBroadcastManager only runs Asynchronously.
I am curious to know why would you use Bound Service for 2 way interaction between Activity and Service when you can do the same kind of interaction with Started Service using local broadcasts and receivers defined in both Activity and Service
It will be helpful to know the pros and cons of each implementation.
I couldn't find any clear answer to this anywhere.
Using a bound Service is much more flexible. You can define methods on the Service (using AIDL) that return immediate results (synchronously), which you cannot do using LocalBroadcastManager. Using LocalBroadcastManager requires that you use your Service in a completely asynchronous way. This decouples the initiation of a service action with the return of the results (callback) which can make your code more complicated and more difficult to understand. Asynchronous use has some benefits, and there are places where you should use it, but if you have a bound Service you can choose exactly when to use synchronous calls and when to use asynchronous callbacks.
Also, the use of AIDL allows you to exactly describe the signatures of the services's method calls. If you use startService(Intent), you cannot guarantee that the caller will provide the correct arguments in the passed Intent, so you need to rely on the caller to "do the right thing" and/or you need to add a lot of additional argument verification.
Don't forget the comment from #CommonsWare about how LocalBroadcastManager only works if the Service is running in the same OS process as the rest of your app (which makes it unsuitable for programming things like system services, which are not running in your OS process).
A service is a component that runs in the background. It works to perform long-running operations without needing to interact with the user For example, a service might retrieve data over the network without stopping or blocking user interaction with an activity of an app or user may play music in the background while the user is in a different application. A service can be of two types or states:
Started: Once started, a service can run in the background indefinitely, even if the component which is started, is destroyed. A service is started when an app module or component, such as an activity, starts it by calling startService(). For example, retrieving contacts from phone book using service when Splash Screen starts.
Bound: A bound service offers a client-server interface that allows components to interact with the service, get results, send requests and even do so across processes with interprocess communication (IPC). A bound service is bound, when an app component binds to it by calling bindService().
I am trying to identify the main conceptual (not implementation) differences between a bound and started service. Here are the main points:
A bound service allows extended two way communication between the activity and the service whereas a started service need not return any results to the client activity
A bound service will service multiple clients (as long as there is at least one client bound to it) while a started service performs a single operation and then shuts down. (I am aware that there can be started services which are also bound)
Are there any other major differences?
A service is a component that runs in the background to perform long-running operations without needing to interact with the user. For example, a service might play music in the background while the user is in a different application, or it might fetch data over the network without blocking user interaction with an activity. A service can essentially take two states:
Started : A service is started when an application component, such as an activity, starts it by calling startService(). Once started, a service can run in the background indefinitely, even if the component that started it is destroyed.
Bound : A service is bound when an application component binds to it by calling bindService(). A bound service offers a client-server interface that allows components to interact with the service, send requests, get results, and even do so across processes with interprocess communication (IPC).
See bellow image perhaps help to you :
The main difference is that bound service will get terminated by Android OS when the last client has unbound, started service however does not need any clients and it can run. As you already mentioned, you can also make a service that can support multi client communication, but is not bound
Difference also arises when you try to stop them. When you call stopService(..) on a bound service and it still has a client bound to it, nothing will happen while on the other hand, the started service will get terminated. When you call unbindService on a started service nothing happens, while if your service bound and this is the last client, it will shut down.... so over all the only difference between them is how they are started and stopped eventually
Apart from that, there is no difference.
My requirement: Detect and respond to power events. I have an activity which allows the user to set up the responses. The app must keep responding after the UI has gone to the background (either by user action, ie "Home", or by, for example, receiving a phone call).
My analysis:
Use a BroadcastReceiver which accepts ACTION_POWER_DISCONNECTED (and ..CONNECTED)
I have implemented the receiver within the activity, and it works as expected. It continues to work in the background for some time, but eventually stops working because of normal android lifecycle, ie. the OS destroys it.
(Proposed) To keep the receiver running, I follow this recommendation and make it a service, with startForeground.
(Proposed) Because it must interact with the UI, ie, by accepting changes to its settings, it should be a bound service.
The expected problem:
According to the documents a bound service is stopped when all clients unbind. I have only one client (the UI), which will unbind in its onDestroy method. This will be called when client is stopped by the OS, which will eventually happen under normal resource management.
A service is "bound" when an application component binds to it by calling bindService(). A bound service offers a client-server interface that allows components to interact with the service, send requests, get results, and even do so across processes with interprocess communication (IPC). A bound service runs only as long as another application component is bound to it. Multiple components can bind to the service at once, but when all of them unbind, the service is destroyed.
Questions
Is this analysis correct? ie. Will a bound service, with one UI client, eventually be destroyed when the client is destroyed, as part of normal OS management?
If so, what should I do about it?
Any other tips please :)
Asked as a hypothetical, because there is quite a bit of work setting up the bound service and then proving that it stops as expected. Also, even it it appears to work, I might be doing this wrong.
Why not register the broadcast receiver in your manifest? It will be started and invoked automatically when the power intents are broadcast. Then you don't need to worry about any sort of "keep alive" processing (and you won't need a service unless you need to do some longer processing)
I want to do Bluetooth connection in Service. And there needs to be interaction between Activities and Services. The service should be started as soon as the app is started and should be able to communicate with UI Activities on certain situations.
What should be the appropriate way of doing it? If I bind the service from only one Activity then that service will be communicating only with that Activity. So, do I need to take AIDL based approach or is there any other way out for this?
Otherwise, can I have a class that extends Application class and then start the service from there and bind the Application class instead?
This is quite a broad question, so I'll answer as best as I can. From what I know of services, multiple activities can bind a single service, all having access to it. Only once all activities that bound the service end their connections (by unbinding), does the service actually stop.
The android documentation on services tells us:
... the system will keep the service running as long as either it is started or there are one or more connections to it with the Context.BIND_AUTO_CREATE flag. Once neither of these situations hold, the service's onDestroy() method is called and the service is effectively terminated
So my recommendation would be to bind the service from all activities that need to communicate with it. When binding with a service an IBinder is returned, which you can use to communicate with the service. Again according to the Android documentation on services:
Usually the IBinder returned is for a complex interface that has been written in aidl.
Although if you only need to perform simple communication with the service, you could use the Messenger class instead of writing full AIDL files. A sample of this can be found here.
Hope this answers your question!
You could bind directly to the Service as the above answer states, however there is no need for Messengers. Your service will be running in the same process as your activity 99.9% of the time. Messengers are designed for inter-process communication (IPC). Also no need for AIDL - that was designed for advanced IPC.
Instead, you should use: BroadcastReceivers and Intents. This is what they were designed for (communication between components in an app).