Android Service learning notes

Service As one of the four major components of Android, it is used to perform a number of tasks that do not require user interaction as well as long running time, an activity can start a service , It will continue to run in the background , Even if the user switches to another application.

Service Can be divided into two basic types:

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1. started 
   If an application component (such as a activity) is called by startService () To start the service, the service is “started”. Once it is started, the service will be able to run in the background, even if it is destroyed. Usually, the started service performs a single operation and does not return a result to the caller. For example, it can download or upload files through the network. When the operation is complete, the service should terminate itself.
2. bound 
   If an application component is called by bindService () Binding to a service, the service is “bound”. The bound service provides a client / A server interface that allows components to interact with the service, send requests, get results, and even use interprocess communication (IPC) to perform these operations across processes. The lifetime of the binding service is consistent with the application component that is bound. Multiple components can bind to a service at the same time, but after all components are unbound, the service will be destroyed.

The following figure is given by the official Service life cycle 

Service Complete survival Period begins at onCreate () At the end of the call, the onDestroy () Return time. Similar to activity, service in onCreate () Complete the initial setup work in the onDestroy () Release all unreleased resources. For example, a music player service can be used in onCreate () Create music player thread in onDestroy () Terminate the thread. Whether it is with startService () Created, or bindService () Created, all services will call onCreate () And onDestroy () Method。

Service Active survival Start at onStartCommand () Or onBind () Call. These two methods will be introduced to startService () Or bindService () The Intent。 If the service is started, the active life and the full life cycle are completed at the same time (even onStartCommand) () After returning, the service is still active If the service is bound, the active lifetime is onUnbind() Return end.

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Define a service

Define a service that declares a class that inherits from Service, which has an abstract method onBind ()

After defining the service, you need to declare in the manifest file

<manifest ... >
  ...
  <application ... >
      <service android:name=".ExampleService" />
      ...
  </application>
</manifest>

stay <service> Elements can contain a number of other attributes, such as defining the attributes required to start a service, the process that the service runs, and so on. Android :name Is the only necessary attribute —— It defines the class name of the service.

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Start and stop service

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Intent startIntent = new Intent(this,MyService.class);
startService(startIntent);// Start service 

Intent stopIntent = new Intent(this,MyService.class);
stopService(stopIntent);// Out of Service 

When the service is started, the onCreate () method and the onStartCommand method are called, but the onCreate method is called only when it is first created, and the onStartCommand method can be called multiple times.

REFER1:http://www.sosoblog.top/?p=759 

REFER2:http://coolnotes.cn/?p=3344