Service

Service本质上是后台运行的可执行程序,它没有Activity那样的用户界面
Service不能与用户进行交互,不能自已启动,运行在后台
启动Service
有两种方法:
1): 通过Context.startService()方法启动一个指定的Service
startService(Intent);
Intent intent = new Intent(起始组件对象,目标Service.class);
startService(intent);

启动后的Service将在后台运行,具有自已的生命周期与当前组件不再有直接关联

eg: startService(new Intent(MainActivity.this,MyService.class));public class MyService extends Service {    private String TAG = "MyService";    public MyService() {    }    @Override    public IBinder onBind(Intent intent) {        // TODO: Return the communication channel to the service.       // throw new UnsupportedOperationException("Not yet implemented");        //不涉及绑定服务,返回null        return null;    }    //Service类创建时触发本方法    @Override    public void onCreate() {        super.onCreate();        Log.i(TAG,"Service is onCreate ");    }    //Service类的实例被启动时触发    @Override    public int onStartCommand(Intent intent, int flags, int startId) {        Log.i(TAG,"Service  onStartCommand");        return super.onStartCommand(intent, flags, startId);    }    //Service的一个实例被收回时,执行此方法    @Override    public void onDestroy() {        super.onDestroy();        Log.i(TAG,"Service onDestory");    }}当点击启动服务按钮时:I/MyService: Service is onCreate I/MyService: Service  onStartCommand点击关闭服务按钮时:I/MyService: Service onDestory

2)通过Context.bindService()方法将一个指定的Service与当前的组件(如Activity)绑定
bindService()方法在绑定时,可以设置启动并绑定,或只绑定不启动
bindService(Intent intent, ServiceConnection conn, int flags);
作用:与intent指定的目标Service绑定
参数1:启动intent对象中指定的目标Service
参数2:是一个ServiceConnection对象,该对象用于监听访问者与Service之间的连接情况
当绑定成功时,调用ServiceConnection对象的onServiceConnected方法当解除绑定时调用onServiceDisconnected方法
参数3:指定绑定时是否自动创建 Service,0:不自动创建Service,BIND_AUTO_CREATE:自动创建Service

onServiceConnected(ComponentName name, IBinder iBinder)
作用:绑定成功时,触发本方法
参数1:被绑定的Service的一个实例
参数2:通过被绑定的Service类中的onBind方法返回一个IBind类型的对象

eg:public class MainActivity extends AppCompatActivity implements View.OnClickListener{    private Button btbind;    private Button btunbind;    MyService.MyBinder mBinder;//定义成员变量    private String TAG = "MyService";    private boolean mIsBind = false;    private ServiceConnection mConn = new ServiceConnection() {        @Override        public void onServiceConnected(ComponentName componentName, IBinder iBinder) {            //绑定成功时触发            mBinder = (MyService.MyBinder)iBinder;            mBinder.print("Hello this is from MainActivity ---");            Log.i(TAG,"onServiceConnected");        }        @Override        public void onServiceDisconnected(ComponentName componentName) {            Log.i(TAG,"onServiceDisconnected");        }    };    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        btbind = (Button)findViewById(R.id.button);        btunbind  = (Button)findViewById(R.id.button2);        btbind.setOnClickListener(this);        btunbind.setOnClickListener(this);    }    @Override    public void onClick(View view) {        switch (view.getId()){            case R.id.button:                bindService(new Intent(MainActivity.this,MyService.class),                        mConn, BIND_AUTO_CREATE);                mIsBind = true;                break;            case R.id.button2:                if(mIsBind){                    unbindService(mConn);                    mIsBind = false;                }                break;        }    }}public class MyService extends Service {    private String TAG = "MyService";    public MyService() {    }    MyBinder mBinder;    //自定义内部类,该类是Binder的子类,用于绑定时传递对象    public class MyBinder extends Binder{        public void print(String text){            Log.i(TAG,text);        }    }    //将对象返回至绑定的Activity    @Override    public IBinder onBind(Intent intent) {       Log.i(TAG,"MyService onBind()");       return mBinder;    }    //Service类创建时触发本方法    @Override    public void onCreate() {        super.onCreate();        Log.i(TAG,"Service is onCreate ");        mBinder = new MyBinder();    }    //Service类的实例被启动时触发    @Override    public int onStartCommand(Intent intent, int flags, int startId) {        Log.i(TAG,"Service  onStartCommand");        return super.onStartCommand(intent, flags, startId);    }   //解除绑定时调用    @Override    public boolean onUnbind(Intent intent) {        Log.i(TAG,"MyService onUnbind");        return super.onUnbind(intent);    }    //再次绑定时调用    @Override    public void onRebind(Intent intent) {        Log.i(TAG,"MyService onRebind()");        super.onRebind(intent);    }}当点击绑定服务时I/MyService: Service is onCreate I/MyService: MyService onBind()I/MyService: Hello this is from MainActivity ---I/MyService: onServiceConnected当点击解除绑定时I/MyService: MyService onUnbind

Service生命周期图