android四大组件之Service

service与activity都是从Context派生出来。
先看service的生命周期：

通过代码看service的几种形式：

1首先，最简单的形式直接启动service；

public class MyService extends Service {

    public MyService() {
    }

    @Override
    public IBinder onBind(Intent intent) {
        // TODO: Return the communication channel to the service.
        throw new UnsupportedOperationException("Not yet implemented");
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {

        Toast.makeText(this,"myService start",Toast.LENGTH_SHORT).show();
        return START_STICKY;
    }
}

2通过bindService（）启动service；

public class BindService extends Service {

    private IBinder binder=new LocalBinder();
    public BindService() {
    }

    public class LocalBinder extends Binder {

        BindService getService(){
            return BindService.this;
        }
    }

    public IBinder onBind(Intent intent){
        return binder;
    }


    public String getString(){
        return "suceessful !!!";
    }
}

3通过intentService；其中intentService是运行另外一个线程，而前面的两个是运行在主线程的；

public class MyIntentService extends IntentService {


    public MyIntentService() {
        super("MyIntentService");
    }

    @Override
    protected void onHandleIntent(Intent intent) {

        System.out.println("IntentService start");
    }


}

看主测试类，这里要注意下bindService的用法；

public class MainActivity extends AppCompatActivity {

    Button btnService,btnIntentService,bindService;
    BindService mService;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        btnService=(Button)findViewById(R.id.service);
        btnIntentService=(Button)findViewById(R.id.IntentService);
        bindService=(Button)findViewById(R.id.bindService);

        btnService.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent=new Intent(getApplicationContext(),MyService.class);
                startService(intent);
            }
        });

        btnIntentService.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                Intent intent1 = new Intent(getApplicationContext(), MyIntentService.class);
                startService(intent1);
            }
        });

        bindService.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {


                Toast.makeText(getApplication(),mService.getString(),Toast.LENGTH_SHORT).show();
            }
        });


    }
    @Override
    protected void onStart(){
        super.onStart();
        Intent intent = new Intent(getApplicationContext(), BindService.class);
        bindService(intent, mConnection, getApplicationContext().BIND_AUTO_CREATE);
    }
    private ServiceConnection mConnection=new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {

            BindService.LocalBinder binder=(BindService.LocalBinder)service;
            mService=binder.getService();

        }

        @Override
        public void onServiceDisconnected(ComponentName name) {

        }
    };

}