Android Service的生命周期和IntentService的用法

service的生命周期，从它被创建开始，到它被销毁为止，可以有两条不同的路径：

A started service

　　被开启的service通过其他组件调用 startService()被创建。

　　这种service可以无限地运行下去，必须调用stopSelf()方法或者其他组件调用stopService()方法来停止它。

　　当service被停止时，系统会销毁它。

 

A bound service

　　被绑定的service是当其他组件（一个客户）调用bindService()来创建的。

　　客户可以通过一个IBinder接口和service进行通信。

　　客户可以通过 unbindService()方法来关闭这种连接。

　　一个service可以同时和多个客户绑定，当多个客户都解除绑定之后，系统会销毁service。

 

　　这两条路径并不是完全分开的。

　　即是说，你可以和一个已经调用了 startService()而被开启的service进行绑定。

　　比如，一个后台音乐service可能因调用 startService()方法而被开启了，稍后，可能用户想要控制播放器或者得到一些当前歌曲的信息，可以通过bindService()将一个activity和service绑定。这种情况下，stopService()或 stopSelf()实际上并不能停止这个service，除非所有的客户都解除绑定。

 

Implementing the lifecycle callbacks

　　和activity一样，service也有一系列的生命周期回调函数，你可以实现它们来监测service状态的变化，并且在适当的时候执行适当的工作。

　　下面的service展示了每一个生命周期的方法：

public class ExampleService extends Service{    int mStartMode; // indicates how to behave if the service is killed    IBinder mBinder; // interface for clients that bind    boolean mAllowRebind; // indicates whether onRebind should be used    @Override    public void onCreate()    {        // The service is being created    }    @Override    public int onStartCommand(Intent intent, int flags, int startId)    {        // The service is starting, due to a call to startService()        return mStartMode;    }    @Override    public IBinder onBind(Intent intent)    {        // A client is binding to the service with bindService()        return mBinder;    }    @Override    public boolean onUnbind(Intent intent)    {        // All clients have unbound with unbindService()        return mAllowRebind;    }    @Override    public void onRebind(Intent intent)    {        // A client is binding to the service with bindService(),        // after onUnbind() has already been called    }    @Override    public void onDestroy()    {        // The service is no longer used and is being destroyed    }}

 

　　不像是activity的生命周期回调函数，你不需要调用基类的实现。

 

　　这个图说明了service典型的回调方法，尽管这个图中将开启的service和绑定的service分开，但是你需要记住，任何service都潜在地允许绑定。

　　所以，一个被开启的service仍然可能被绑定。

　　实现这些方法，你可以看到两层嵌套的service的生命周期：

 

The entire lifetime

　　service整体的生命时间是从onCreate()被调用开始，到onDestroy()方法返回为止。

　　和activity一样，service在onCreate()中进行它的初始化工作，在onDestroy()中释放残留的资源。

　　比如，一个音乐播放service可以在onCreate()中创建播放音乐的线程，在onDestory()中停止这个线程。

 　　onCreate() 和 onDestroy()会被所有的service调用，不论service是通过startService()还是bindService()建立。

 

The active lifetime

　　service积极活动的生命时间（active lifetime）是从onStartCommand() 或onBind()被调用开始，它们各自处理由startService()或 bindService()方法传过来的Intent对象。

　　如果service是被开启的，那么它的活动生命周期和整个生命周期一同结束。

　　如果service是被绑定的，它们它的活动生命周期是在onUnbind()方法返回后结束。

　　注意：尽管一个被开启的service是通过调用 stopSelf() 或 stopService()来停止的，没有一个对应的回调函数与之对应，即没有onStop()回调方法。所以，当调用了停止的方法，除非这个service和客户组件绑定，否则系统将会直接销毁它，onDestory()方法会被调用，并且是这个时候唯一会被调用的回调方法。

 

Managing the Lifecycle of a Bound Service

　　当绑定service和所有客户端解除绑定之后，Android系统将会销毁它，（除非它同时被onStartCommand()方法开启）。

　　因此，如果你的service是一个纯粹的绑定service，那么你不需要管理它的生命周期。

　　然而，如果你选择实现onStartCommand()回调方法，那么你必须显式地停止service，因为service此时被看做是开启的。

　　这种情况下，service会一直运行到它自己调用 stopSelf()或另一个组件调用stopService()，不论它是否和客户端绑定。

　　另外，如果你的service被开启并且接受绑定，那么当系统调用你的 onUnbind()方法时，如果你想要在下次客户端绑定的时候接受一个onRebind()的调用（而不是调用 onBind()），你可以选择在 onUnbind()中返回true。

　　onRebind()的返回值为void，但是客户端仍然在它的 onServiceConnected()回调方法中得到 IBinder 对象。

　　下图展示了这种service（被开启，还允许绑定）的生命周期：

IntentService

ntentService是Service类的子类，用来处理异步请求。客户端可以通过startService(Intent)方法传递请求给IntentService。IntentService在onCreate()函数中通过HandlerThread单独开启一个线程来处理所有Intent请求对象（通过startService的方式发送过来的）所对应的任务，这样以免事务处理阻塞主线程。执行完所一个Intent请求对象所对应的工作之后，如果没有新的Intent请求达到，则自动停止Service；否则执行下一个Intent请求所对应的任务。

　　IntentService在处理事务时，还是采用的Handler方式，创建一个名叫ServiceHandler的内部Handler，并把它直接绑定到HandlerThread所对应的子线程。 ServiceHandler把处理一个intent所对应的事务都封装到叫做onHandleIntent的虚函数；因此我们直接实现虚函数onHandleIntent，再在里面根据Intent的不同进行不同的事务处理就可以了。

另外，IntentService默认实现了Onbind（）方法，返回值为null。

　　使用IntentService需要两个步骤：

　　1、写构造函数

　　2、实现虚函数onHandleIntent，并在里面根据Intent的不同进行不同的事务处理就可以了。

好处：处理异步请求的时候可以减少写代码的工作量，比较轻松地实现项目的需求

注意：IntentService的构造函数一定是参数为空的构造函数，然后再在其中调用super("name")这种形式的构造函数。

因为Service的实例化是系统来完成的，而且系统是用参数为空的构造函数来实例化Service的

关于Handler和Service的更多知识请阅读《Looper和Handler》，《关于Handler技术》，《Service简介》，《AIDL和Service实现两进程通信》

Public ConstructorsIntentService(String name)

Creates an IntentService.

Public MethodsIBinderonBind(Intent intent)

Unless you provide binding for your service, you don't need to implement this method, because the default implementation returns null.

voidonCreate()

Called by the system when the service is first created.

voidonDestroy()

Called by the system to notify a Service that it is no longer used and is being removed.

voidonStart(Intent intent, int startId)

This method is deprecated. Implement onStartCommand(Intent, int, int) instead.

intonStartCommand(Intent intent, int flags, int startId)

You should not override this method for your IntentService.

voidsetIntentRedelivery(boolean enabled)

Sets intent redelivery preferences.

If enabled is true, onStartCommand(Intent, int, int) will return START_REDELIVER_INTENT, so if this process dies before onHandleIntent(Intent)returns, the process will be restarted and the intent redelivered. If multiple Intents have been sent, only the most recent one is guaranteed to be redelivered.

If enabled is false (the default), onStartCommand(Intent, int, int) will return START_NOT_STICKY, and if the process dies, the Intent dies along with it.

设置为true时，onStartCommand返回START_REDELIVER_INTENT，否则返回START_NOT_STICKY

关于此的更多内容请参考《Service简介》

Protected Methodsabstract voidonHandleIntent(Intent intent)

This method is invoked on the worker thread with a request to process.

This method is invoked on the worker thread with a request to process. Only one Intent is processed at a time, but the processing happens on a worker thread that runs independently from other application logic. So, if this code takes a long time, it will hold up other requests to the same IntentService, but it will not hold up anything else. When all requests have been handled, the IntentService stops itself, so you should not call stopSelf().

该函数用于针对Intent的不同进行不同的事务处理就可以了.执行完所一个Intent请求对象所对应的工作之后，如果没有新的Intent请求达到，

则自动停止Service；否则ServiceHandler会取得下一个Intent请求传人该函数来处理其所对应的任务。

实例1

MyIntentService.java文件

<div><span class="kwd" style="color:#0088;">package</span><span class="pln"> com</span><span class="pun" style="color:#66660;">.</span><span class="pln">lenovo</span><span class="pun" style="color:#66660;">.</span><span class="pln">robin</span><span class="pun" style="color:#66660;">.</span><span class="pln">test</span><span class="pun" style="color:#66660;">;</span></div><div><span class="kwd" style="color:#0088;">import</span><span class="pln"> android</span><span class="pun" style="color:#66660;">.</span><span class="pln">app</span><span class="pun" style="color:#66660;">.</span><span class="typ" style="color:#66066;">IntentService</span><span class="pun" style="color:#66660;">;</span></div><div><span class="kwd" style="color:#0088;">import</span><span class="pln"> android</span><span class="pun" style="color:#66660;">.</span><span class="pln">content</span><span class="pun" style="color:#66660;">.</span><span class="typ" style="color:#66066;">Intent</span><span class="pun" style="color:#66660;">;</span></div><div><span class="kwd" style="color:#0088;">import</span><span class="pln"> android</span><span class="pun" style="color:#66660;">.</span><span class="pln">util</span><span class="pun" style="color:#66660;">.</span><span class="typ" style="color:#66066;">Log</span><span class="pun" style="color:#66660;">;</span></div><div></div><div><span class="kwd" style="color:#0088;">public</span><span class="pln"> </span><span class="kwd" style="color:#0088;">class</span><span class="pln"> </span><span class="typ" style="color:#66066;">MyIntentService</span><span class="pln"> </span><span class="kwd" style="color:#0088;">extends</span><span class="pln"> </span><span class="typ" style="color:#66066;">IntentService</span><span class="pln"> </span><span class="pun" style="color:#66660;">{</span></div><div><span class="kwd" style="color:#0088;">final</span><span class="pln"> </span><span class="kwd" style="color:#0088;">static</span><span class="pln"> </span><span class="typ" style="color:#66066;">String</span><span class="pln"> TAG</span><span class="pun" style="color:#66660;">=</span><span class="str" style="color:#0880;">"robin"</span><span class="pun" style="color:#66660;">;</span></div><div><span class="pln"> </span><span class="kwd" style="color:#0088;">public</span><span class="pln"> </span><span class="typ" style="color:#66066;">MyIntentService</span><span class="pun" style="color:#66660;">()</span><span class="pln"> </span><span class="pun" style="color:#66660;">{</span></div><div><span class="pln">  </span><span class="kwd" style="color:#0088;">super</span><span class="pun" style="color:#66660;">(</span><span class="str" style="color:#0880;">"com.lenovo.robin.test.MyIntentService"</span><span class="pun" style="color:#66660;">);</span></div><div><span class="pln">  </span><span class="typ" style="color:#66066;">Log</span><span class="pun" style="color:#66660;">.</span><span class="pln">i</span><span class="pun" style="color:#66660;">(</span><span class="pln">TAG</span><span class="pun" style="color:#66660;">,</span><span class="kwd" style="color:#0088;">this</span><span class="pun" style="color:#66660;">+</span><span class="str" style="color:#0880;">" is constructed"</span><span class="pun" style="color:#66660;">);</span></div><div><span class="pln"> </span><span class="pun" style="color:#66660;">}</span></div><div><span class="pln"> </span><span class="lit" style="color:#06666;">@Override</span></div><div><span class="pln"> </span><span class="kwd" style="color:#0088;">protected</span><span class="pln"> </span><span class="kwd" style="color:#0088;">void</span><span class="pln"> onHandleIntent</span><span class="pun" style="color:#66660;">(</span><span class="typ" style="color:#66066;">Intent</span><span class="pln"> arg0</span><span class="pun" style="color:#66660;">)</span><span class="pln"> </span><span class="pun" style="color:#66660;">{</span></div><div><span class="pln">  </span><span class="typ" style="color:#66066;">Log</span><span class="pun" style="color:#66660;">.</span><span class="pln">i</span><span class="pun" style="color:#66660;">(</span><span class="pln">TAG</span><span class="pun" style="color:#66660;">,</span><span class="str" style="color:#0880;">"begin onHandleIntent() in "</span><span class="pun" style="color:#66660;">+</span><span class="kwd" style="color:#0088;">this</span><span class="pun" style="color:#66660;">);</span></div><div><span class="pln">  </span><span class="kwd" style="color:#0088;">try</span><span class="pln"> </span><span class="pun" style="color:#66660;">{</span></div><div><span class="pln">   </span><span class="typ" style="color:#66066;">Thread</span><span class="pun" style="color:#66660;">.</span><span class="pln">sleep</span><span class="pun" style="color:#66660;">(</span><span class="lit" style="color:#06666;">10</span><span class="pun" style="color:#66660;">*</span><span class="lit" style="color:#06666;">1000</span><span class="pun" style="color:#66660;">);</span></div><div><span class="pln">  </span><span class="pun" style="color:#66660;">}</span><span class="pln"> </span><span class="kwd" style="color:#0088;">catch</span><span class="pln"> </span><span class="pun" style="color:#66660;">(</span><span class="typ" style="color:#66066;">InterruptedException</span><span class="pln"> e</span><span class="pun" style="color:#66660;">)</span><span class="pln"> </span><span class="pun" style="color:#66660;">{</span></div><div><span class="pln">  </span><span class="pln">   e</span><span class="pun" style="color:#66660;">.</span><span class="pln">printStackTrace</span><span class="pun" style="color:#66660;">();</span></div><div><span class="pln">  </span><span class="pun" style="color:#66660;">}</span></div><div><span class="pln">  </span><span class="typ" style="color:#66066;">Log</span><span class="pun" style="color:#66660;">.</span><span class="pln">i</span><span class="pun" style="color:#66660;">(</span><span class="pln">TAG</span><span class="pun" style="color:#66660;">,</span><span class="str" style="color:#0880;">"end onHandleIntent() in "</span><span class="pun" style="color:#66660;">+</span><span class="kwd" style="color:#0088;">this</span><span class="pun" style="color:#66660;">);</span></div><div><span class="pln"> </span><span class="pun" style="color:#66660;">}</span></div><div><span class="pln"> </span><span class="kwd" style="color:#0088;">public</span><span class="pln"> </span><span class="kwd" style="color:#0088;">void</span><span class="pln"> onDestroy</span><span class="pun" style="color:#66660;">()</span></div><div><span class="pln"> </span><span class="pun" style="color:#66660;">{</span></div><div><span class="pln">  </span><span class="kwd" style="color:#0088;">super</span><span class="pun" style="color:#66660;">.</span><span class="pln">onDestroy</span><span class="pun" style="color:#66660;">();</span></div><div><span class="pln">  </span><span class="typ" style="color:#66066;">Log</span><span class="pun" style="color:#66660;">.</span><span class="pln">i</span><span class="pun" style="color:#66660;">(</span><span class="pln">TAG</span><span class="pun" style="color:#66660;">,</span><span class="kwd" style="color:#0088;">this</span><span class="pun" style="color:#66660;">+</span><span class="str" style="color:#0880;">" is destroy"</span><span class="pun" style="color:#66660;">);</span></div><div><span class="pln"> </span><span class="pun" style="color:#66660;">}</span></div><div><span class="pun" style="color:#66660;">}</span></div>

启动MyIntentServic的代码片段

<div><span class="pln">   </span><span class="typ" style="color:#66066;">Intent</span><span class="pln"> intent</span><span class="pun" style="color:#66660;">=</span><span class="kwd" style="color:#0088;">new</span><span class="pln"> </span><span class="typ" style="color:#66066;">Intent</span><span class="pun" style="color:#66660;">(</span><span class="kwd" style="color:#0088;">this</span><span class="pun" style="color:#66660;">,</span><span class="typ" style="color:#66066;">MyIntentService</span><span class="pun" style="color:#66660;">.</span><span class="kwd" style="color:#0088;">class</span><span class="pun" style="color:#66660;">);</span></div><div><span class="pln">   </span><span class="pln">startService</span><span class="pun" style="color:#66660;">(</span><span class="pln">intent</span><span class="pun" style="color:#66660;">);</span></div><div><span class="pln">   </span><span class="pln">startService</span><span class="pun" style="color:#66660;">(</span><span class="pln">intent</span><span class="pun" style="color:#66660;">);</span></div><div><span class="pln">   </span><span class="pln">startService</span><span class="pun" style="color:#66660;">(</span><span class="pln">intent</span><span class="pun" style="color:#66660;">);</span></div>

AndroidManifest.xml文件代码片段

<p style="margin-top:0px; margin-bottom:10px; padding-top:0px; padding-bottom:0px"><span class="tag" style="color:#0088;"><service</span><span class="pln"> </span><span class="atn" style="color:#66066;">android:name</span><span class="pun" style="color:#66660;">=</span><span class="atv" style="color:#0880;">".MyIntentService"</span><span class="pln"> </span><span class="tag" style="color:#0088;">/></span></p>

运行结果

09-14 22:23:34.730: I/robin(30943): com.lenovo.robin.test.MyIntentService@40541370 is constructed

09-14 22:23:34.730: I/robin(30943): begin onHandleIntent() in com.lenovo.robin.test.MyIntentService@40541370

09-14 22:23:44.730: I/robin(30943): end onHandleIntent() in com.lenovo.robin.test.MyIntentService@40541370

09-14 22:23:44.730: I/robin(30943): begin onHandleIntent() in com.lenovo.robin.test.MyIntentService@40541370

09-14 22:23:54.740: I/robin(30943): end onHandleIntent() in com.lenovo.robin.test.MyIntentService@40541370

09-14 22:23:54.740: I/robin(30943): begin onHandleIntent() in com.lenovo.robin.test.MyIntentService@40541370

09-14 22:24:04.739: I/robin(30943): end onHandleIntent() in com.lenovo.robin.test.MyIntentService@40541370

09-14 22:24:04.739: I/robin(30943): com.lenovo.robin.test.MyIntentService@40541370 is destroy