Detailed explanation of Service (Background Service) in Android

Detailed explanation of Service (Background Service) in Android

This article mainly introduces the Service (Background Service) details in Android. This article describes the concept, role, lifecycle, startup method, and code instance of the Service. For more information, see

1. concept:

(1). Service is an Activity that runs in the background. It is not a separate process. It only requires the application to tell it what to do in the background.

(2) If it is used to achieve interaction with the user, it needs to receive the display through the notification bar or by sending the broadcast, the UI.

(3). It is widely used, especially at the framework layer. More applications are called to system services.

2. role:

(1) It is used to handle background operations that do not interfere with the user's use. Such as download and network retrieval. It can be used to play music. It can be enabled through INTENT and bound to a host object (caller such as ACTIVITY.

(2) If Activity displays information on the front-end page, the Service performs operations in the background. If the Service interacts with the front-end UI, you can send a broadcast or notification bar.

3. lifecycle:

(1) The overall life time of the service starts when onCreate () is called and ends when the onDestroy () method is returned. Like activity, the service initializes it in onCreate () and releases residual resources in onDestroy.

(2). ** startService () method: ** onCreate ()-> onStartCommand ()-> onStart ()-> onDestroy ()

(3). ** BindService () method: ** onCreate ()-> onBinder ()-> onUnbind ()-> onDestroy (). The onUnbind () method returns and ends.

4. Startup Mode:

(1) the Service itself cannot run. It needs to be called through an Activity or other Context object.

(2) There are two ways to start the Service:

Context. startService () and Context. bindService () start the Service. If there are time-consuming operations in the onCreate () method or onStart () method of the service, you need to open a new thread. You can start a service in the preceding two ways.

Note:

Generally, the startService method is used to place time-consuming tasks in the background for processing. After the processing is completed, you can use the broadcast or notification bar to notify the foreground.

5. The following code is used for in-depth understanding:

(1). MainActivity. java class:

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Package com. example. servicetest;   Import com. example. servicetest. service. MyService;   Import android. app. Activity; Import android. content. ComponentName; Import android. content. Intent; Import android. content. ServiceConnection; Import android. OS. Bundle; Import android. OS. IBinder; Import android. util. Log; Import android. view. View; Import android. view. View. OnClickListener; Import android. widget. Button;   Public class MainActivity extends Activity implements OnClickListener { /** Flag space */ Private static String TAG = "com. example. servicetest. MainActivity "; /** Start the service */ Private Button mBtnStart; /** Bind a service */ Private Button mBtnBind;   @ Override Protected void onCreate (Bundle savedInstanceState ){ Super. onCreate (savedInstanceState ); SetContentView (R. layout. activity_main ); InitView (); }   /** * Init the View */ Private void initView (){ MBtnStart = (Button) findViewById (R. id. startservice ); MBtnBind = (Button) findViewById (R. id. bindservice ); MBtnStart. setOnClickListener (this ); MBtnBind. setOnClickListener (this );   }   @ Override Public void onClick (View view ){ Switch (view. getId ()){ // Method of starting the service Case R. id. startservice: StartService (new Intent (MyService. ACTION )); Break; // Service binding method Case R. id. bindservice: BindService (new Intent (MyService. ACTION), conn, BIND_AUTO_CREATE );   Break;   Default:   Break; }   }   ServiceConnection conn = new ServiceConnection (){ Public void onServiceConnected (ComponentName name, IBinder service ){ Log. v (TAG, "onServiceConnected "); }   Public void onServiceDisconnected (ComponentName name ){ Log. v (TAG, "onServiceDisconnected "); } };   @ Override Protected void onDestroy (){ Super. onDestroy (); System. out. println ("------- onDestroy ()--"); StopService (new Intent (MyService. ACTION )); UnbindService (conn ); } }

(2). MyService. java class:

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Package com. example. servicetest. service;   Import android. app. Service; Import android. content. Intent; Import android. OS. Binder; Import android. OS. IBinder; Import android. util. Log;   Public class MyService extends Service { /** Flag space */ Private static String TAG = "com. example. servicetest. service. MyService "; /** Behavior */ Public static final String ACTION = "com. example. servicetest. service. MyService ";   @ Override Public void onCreate (){ Super. onCreate ();   System. out. println ("----- onCreate ()---");   }   @ Override Public void onStart (Intent intent, int startId ){ Super. onStart (intent, startId ); System. out. println ("----- onStart ()---"); }   @ Override Public int onStartCommand (Intent intent, int flags, int startId ){ System. out. println ("----- onStartCommand ()---"); Return super. onStartCommand (intent, flags, startId ); }   @ Override Public IBinder onBind (Intent arg0 ){ System. out. println ("----- onBind ()---"); Return null; }     @ Override Public void onRebind (Intent intent ){ System. out. println ("----- onRebind ()---"); Super. onRebind (intent ); }   @ Override Public boolean onUnbind (Intent intent ){ System. out. println ("----- onUnbind ()---"); Return super. onUnbind (intent ); }   @ Override Public void onDestroy (){ System. out. println ("----- onDestroy ()---"); Super. onDestroy (); }   }

(3). AndroidManifest. xml

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<! -- Register --> <Service android: name = "com. example. servicetest. service. MyService"> <Intent-filter>   <! -- Intent used to start the service --> <Action android: name = "com. example. servicetest. service. MyService"/>   <Category android: name = "android. intent. category. default"/> </Intent-filter> </Service>

StartService method:

(1) When you press the startService button:

(2) When you continue to press the startService button:

BindService method:

(1) When you press the bindService button:

(2) When you continue to press the bindService button:

(3) First press startService and then bindService: