Android-理解Service的生命周期

 1 public class startService1 extends Service {
    static final String TAG="startService1 :";
    public startService1() {
        super();
    }

    @Override
    public void onCreate() {
        L.e(TAG,"onCreate");
        super.onCreate();
    }

    @Override
    public void onStart(Intent intent, int startId) {
        L.e(TAG,"onStart");
        super.onStart(intent, startId);
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        L.e(TAG,"onStartCommand");
        return super.onStartCommand(intent, flags, startId);
    }

    @Override
    public void onDestroy() {
        L.e(TAG, "onDestroy");
        super.onDestroy();
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        L.e(TAG, "onConfigurationChanged");
        super.onConfigurationChanged(newConfig);
    }

    @Override
    public void onLowMemory() {
        L.e(TAG, "onLowMemory");
        super.onLowMemory();
    }

    @Override
    public void onTrimMemory(int level) {
        L.e(TAG, "onTrimMemory");
        super.onTrimMemory(level);
    }

    @Override
    public IBinder onBind(Intent intent) {
        L.e(TAG, "onBind");
        return null;
    }

    @Override
    public boolean onUnbind(Intent intent) {
        L.e(TAG,"onUnbind");
        return super.onUnbind(intent);
    }

    @Override
    public void onRebind(Intent intent) {
        L.e(TAG, "onRebind");
        super.onRebind(intent);
    }

    @Override
    public void onTaskRemoved(Intent rootIntent) {
        L.e(TAG, "onTaskRemoved");
        super.onTaskRemoved(rootIntent);
    }

    @Override
    protected void dump(FileDescriptor fd, PrintWriter writer, String[] args) {
        L.e(TAG, "dump");
        super.dump(fd, writer, args);
    }
}
1.Activity.startService方式启动 service启动顺序如下：

06-04 11:16:00.147 17810-17810/com.alipay E/startService1 :﹕ --> onCreate
06-04 11:16:00.147 17810-17810/com.alipay E/startService1 :﹕ --> onStartCommand
06-04 11:16:00.147 17810-17810/com.alipay E/startService1 :﹕ --> onStart

如果连续startService(intent);startService(intent); 可见service只会create一次，start不限

06-04 11:49:27.877 19224-19224/com.alipay E/startService1 :﹕ --> onCreate
06-04 11:49:27.877 19224-19224/com.alipay E/startService1 :﹕ --> onStartCommand
06-04 11:49:27.887 19224-19224/com.alipay E/startService1 :﹕ --> onStart
06-04 11:49:27.887 19224-19224/com.alipay E/startService1 :﹕ --> onStartCommand
06-04 11:49:27.887 19224-19224/com.alipay E/startService1 :﹕ --> onStart

如果stopService(intent);可见service在onDestroy结束生命周期

06-04 11:53:06.027  19677-19677/com.alipay E/startService1 :﹕ --> onDestroy
   可见本地Service控制方式很单一，并没有activity的保存唤醒功能。

如果finish开始service的activity,service并没有被销毁，可见startService方式启动service,只能调用stopservice来stop，跟所启动的activity的生命周期无关。
也就是说，一旦startService,这个Service就与此activity基本无关了。所以非常适合做常驻后台操作（非常耗时操作还是要启用新的线程，经测试service耗时也会导致ANR，很容易理解因为四大基本组件公用UI线程的MessageQueue嘛）
这里注意onXXXX操作并不都是立即执行，需要考虑到延时。
service->ContextWrapper->context,Activity->ContextThemeWrapper->ContextWrapper->context。而ContextThmeWrapper也就增加了一个initializeTheme方法，可见activity可以看做是有theme有view的service；

06-04 12:12:20.767  20538-20538/com.alipay E/AM_MEMORYIPROCESS﹕ --> onDestroy
2.Activity.bindService方式启动
  我们先看一下bindService的参数，多了一个ServiceConnection.必须ServiceConnection非空,否则会抛出异常 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.alipay/com.alipay.startActivity}: java.lang.IllegalArgumentException: connection is null .ServiceConnection包括连接和断开连接的回调函数,如下.

public boolean bindService(Intent service, ServiceConnection conn,
        int flags)

ServiceConnection serviceConnection=new ServiceConnection() {
    @Override
    public void onServiceConnected(ComponentName name, IBinder service) {

    }

    @Override
    public void onServiceDisconnected(ComponentName name) {

    }
};
我们再来看看conn的flag.定义值之外不能成功bind.
public static final int BIND_AUTO_CREATE = 0x0001;
 public static final int BIND_DEBUG_UNBIND = 0x0002;

public static final int BIND_NOT_FOREGROUND = 0x0004;

public static final int BIND_ABOVE_CLIENT = 0x0008;

public static final int BIND_ALLOW_OOM_MANAGEMENT = 0x0010;

public static final int BIND_WAIVE_PRIORITY = 0x0020;

public static final int BIND_IMPORTANT = 0x0040;

public static final int BIND_ADJUST_WITH_ACTIVITY = 0x0080;

再来看看service的onbind方法。如果没有返回binder,onBind时serviceConnection的onServiceConnected方法并没有回调。

@Override
public IBinder onBind(Intent intent) {
    L.e(TAG, "onBind");
    return null;
}

06-04 15:26:42.803 23684-23684/com.alipay E/Service2﹕ --> onCreate
06-04 15:26:42.803 23684-23684/com.alipay E/Service2﹕ --> onBind

如果onBind返回binder，onServiceConnected回调成功。此处我理解是activity和service ipc的一种方式，serviceConnection此处定义在activity内，onbind定义在service内，
当activity bindservice时，回调onServiceConnected,完成彼此的通信。binder的proxy模式此处不详细讨论了。

@Override
public IBinder onBind(Intent intent) {
    L.e(TAG, "onBind");
    return binder;
}

06-04 15:31:15.633 23813-23813/com.alipay E/Service2﹕ --> onCreate
06-04 15:31:15.643 23813-23813/com.alipay E/Service2﹕ --> onBind
06-04 15:31:15.713 23813-23813/com.alipay E/AM_MEMORYIPROCESS﹕ --> onServiceConnected

我们再来看看unbind时候的生命周期，先unbind,再调用onDestroy结束service.我们可知，不管什么方式启动service，service只能create一次（注意service没有onstop onResume onPause等操作）
还要注意一点 onbind方式启动service，根本不会启动onstart.
再次验证 onbind时候执行超时操作一样会ANR,得出结论执行异步超时操作一定要新建线程，下一节讲怎么新建线程。

06-04 15:37:52.683 24057-24057/com.alipay E/Service2﹕ --> onCreate
06-04 15:37:52.683 24057-24057/com.alipay E/Service2﹕ --> onBind
06-04 15:37:52.683 24057-24057/com.alipay E/Service2﹕ --> onUnbind
06-04 15:37:52.683 24057-24057/com.alipay E/Service2﹕ --> onDestroy

3.同时启动onstart onBind Service,必须同时解绑才能销毁service.

bindService(intent, serviceConnection,BIND_AUTO_CREATE);
startService(intent);
stopService(intent);
unbindService(serviceConnection);

06-04 15:56:54.663 25250-25250/com.alipay E/Service2﹕ --> onCreate
06-04 15:56:54.663 25250-25250/com.alipay E/Service2﹕ --> onBind
06-04 15:56:54.673 25250-25250/com.alipay E/Service2﹕ --> onStartCommand
06-04 15:56:54.673 25250-25250/com.alipay E/Service2﹕ --> onStart
06-04 15:56:54.673 25250-25250/com.alipay E/Service2﹕ --> onUnbind
06-04 15:56:54.673 25250-25250/com.alipay E/Service2﹕ --> onDestroy

其实很容易理解，onstart启动本地service，onbind启动远程代理类service，必须将这两个service的资源都释放掉才能销毁service。

我们可以得出结论，onCreate和onDestroy是对应的，在service生命周期只会出现一次，分别在生命的开始和结束。onbind和onUnbind的是对应的。