前言
我们可以通过调用Context的startService来启动Service，也可以通过Context的bindService来绑定Service，建议阅读此篇文章前请阅读这篇文章，知识点重叠的部分，本篇文章将不再赘述。
1.ContextImpl到ActivityManageService的调用过程
我们可以用bindService方法来绑定Service，它的实现在ContextWrapper中，代码如下所示。
frameworks/base/core/java/android/content/ContextWrapper.java
@Override public boolean bindService(Intent service, ServiceConnection conn, int flags) { return mBase.bindService(service, conn, flags); } 这里mBase具体指向就是ContextImpl，不明白的请查看 这篇文章。接着查看ContextImpl的bindService方法：
frameworks/base/core/java/android/app/ContextImpl.java @Overridepublic boolean bindService(Intent service, ServiceConnection conn, int flags) { warnIfCallingFromSystemProcess(); return bindServiceCommon(service, conn, flags, mMainThread.getHandler(), Process.myUserHandle()); } 在bindService方法中，又return了bindServiceCommon方法，代码如下所示。
frameworks/base/core/java/android/app/ContextImpl.java private boolean bindServiceCommon(Intent service, ServiceConnection conn, int flags, Handler handler, UserHandle user) { IServiceConnection sd; if (conn == null) { throw new IllegalArgumentException("connection is null"); } if (mPackageInfo != null) { sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(), handler, flags);//1 } else { throw new RuntimeException("Not supported in system context"); } validateServiceIntent(service); try { ... /** * 2 */ int res = ActivityManagerNative.getDefault().bindService( mMainThread.getApplicationThread(), getActivityToken(), service, service.resolveTypeIfNeeded(getContentResolver()), sd, flags, getOpPackageName(), user.getIdentifier()); ... } catch (RemoteException e) { throw e.rethrowFromSystemServer(); }} 在注释1处调用了LoadedApk类型的对象mPackageInfo的getServiceDispatcher方法，它的主要作用是将ServiceConnection封装为IServiceConnection类型的对象sd，从IServiceConnection的名字我们就能得知它实现了Binder机制，这样Service的绑定就支持了跨进程。接着在注释2处我们又看见了熟悉的代码，最终会调用AMS的bindService方法。
ContextImpl到ActivityManageService的调用过程如下面的时序图所示。绘图1_副本.png
2.Service的绑定过程
AMS的bindService方法代码如下所示。
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java public int bindService(IApplicationThread caller, IBinder token, Intent service, String resolvedType, IServiceConnection connection, int flags, String callingPackage, int userId) throws TransactionTooLargeException { enforceNotIsolatedCaller("bindService");... synchronized(this) { return mServices.bindServiceLocked(caller, token, service, resolvedType, connection, flags, callingPackage, userId); } } bindService方法最后会调用ActiveServices类型的对象mServices的bindServiceLocked方法：
frameworks/base/services/core/java/com/android/server/am/ActiveServices.java int bindServiceLocked(IApplicationThread caller, IBinder token, Intent service, String resolvedType, final IServiceConnection connection, int flags, String callingPackage, final int userId) throws TransactionTooLargeException { ... if ((flags&Context.BIND_AUTO_CREATE) != 0) { s.lastActivity = SystemClock.uptimeMillis(); /** * 1 */ if (bringUpServiceLocked(s, service.getFlags(), callerFg, false, permissionsReviewRequired) != null) { return 0; } } ... if (s.app != null && b.intent.received) { //2 try { c.conn.connected(s.name, b.intent.binder);//3 } catch (Exception e) { ... } if (b.intent.apps.size() == 1 && b.intent.doRebind) { //4 requestServiceBindingLocked(s, b.intent, callerFg, true);//5 } } else if (!b.intent.requested) { //6 requestServiceBindingLocked(s, b.intent, callerFg, false);//7 } getServiceMap(s.userId).ensureNotStartingBackground(s); } finally { Binder.restoreCallingIdentity(origId); } return 1;} 在注释1处会bringUpServiceLocked方法，在bringUpServiceLocked方法中又会调用realStartServiceLocked方法，最终由ActivityThread来调用Service的onCreate方法启动Service，这一过程在这篇文章中已经讲过，这里不再赘述。
在注释2处s.app != null 表示Service已经运行，其中s是ServiceRecord类型对象，app是ProcessRecord类型对象。b.intent.received表示当前应用程序进程的Client端已经接收到绑定Service时返回的Binder，这样应用程序进程的Client端就可以通过Binder来获取要绑定的Service的访问接口。注释3处调用c.conn的connected方法，其中c.conn指的是IServiceConnection，它的具体实现为ServiceDispatcher.InnerConnection，其中ServiceDispatcher是LoadedApk的内部类，InnerConnection的connected方法内部会调用H的post方法向主线程发送消息，从而解决当前应用程序进程和Service跨进程通信的问题，在后面会详细介绍这一过程。在注释4处如果当前应用程序进程的Client端第一次与Service进行绑定的，并且Service已经调用过onUnBind方法，则需要调用注释5的代码。注释6处如果应用程序进程的Client端没有发送过绑定Service的请求，则会调用注释7的代码，注释7和注释5的代码区别就是最后一个参数rebind为false，表示不是重新绑定。接着我们查看注释7的requestServiceBindingLocked方法，代码如下所示。frameworks/base/services/core/java/com/android/server/am/ActiveServices.java private final boolean requestServiceBindingLocked(ServiceRecord r, IntentBindRecord i, boolean execInFg, boolean rebind) throws TransactionTooLargeException { ... if ((!i.requested || rebind) && i.apps.size() > 0) { //1 try { bumpServiceExecutingLocked(r, execInFg, "bind"); r.app.forceProcessStateUpTo(ActivityManager.PROCESS_STATE_SERVICE); r.app.thread.scheduleBindService(r, i.intent.getIntent(), rebind, r.app.repProcState);//2 ... } ... } return true;} 注释1处i.requested表示是否发送过绑定Service的请求，从前面的代码得知是没有发送过，因此，!i.requested为true。从前面的代码得知rebind值为false，那么(!i.requested || rebind)的值为true。如果IntentBindRecord中的应用程序进程记录大于0，则会调用注释2的代码，r.app.thread的类型为IApplicationThread，它的实现我们已经很熟悉了，是ActivityThread的内部类ApplicationThread，scheduleBindService方法如下所示。
frameworks/base/core/java/android/app/ActivityThread.java public final void scheduleBindService(IBinder token, Intent intent, boolean rebind, int processState) { updateProcessState(processState, false); BindServiceData s = new BindServiceData(); s.token = token; s.intent = intent; s.rebind = rebind; if (DEBUG_SERVICE) Slog.v(TAG, "scheduleBindService token=" + token + " intent=" + intent + " uid=" + Binder.getCallingUid() + " pid=" + Binder.getCallingPid()); sendMessage(H.BIND_SERVICE, s); } 首先将Service的信息封装成BindServiceData对象，需要注意的BindServiceData的成员变量rebind的值为false，后面会用到它。接着将BindServiceData传入到sendMessage方法中。sendMessage向H发送消息，我们接着查看H的handleMessage方法。
frameworks/base/core/java/android/app/ActivityThread.java public void handleMessage(Message msg) { if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what)); switch (msg.what) { ... case BIND_SERVICE: Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceBind"); handleBindService((BindServiceData)msg.obj); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); break; ... } ... } ... } H在接收到BIND_SERVICE类型消息时，会在handleMessage方法中会调用handleBindService方法：
frameworks/base/core/java/android/app/ActivityThread.java private void handleBindService(BindServiceData data) { Service s = mServices.get(data.token);//1 if (DEBUG_SERVICE) Slog.v(TAG, "handleBindService s=" + s + " rebind=" + data.rebind); if (s != null) { try { data.intent.setExtrasClassLoader(s.getClassLoader()); data.intent.prepareToEnterProcess(); try { if (!data.rebind) { //2 IBinder binder = s.onBind(data.intent);//3 ActivityManagerNative.getDefault().publishService( data.token, data.intent, binder);//4 } else { s.onRebind(data.intent);//5 ActivityManagerNative.getDefault().serviceDoneExecuting( data.token, SERVICE_DONE_EXECUTING_ANON, 0, 0); } ensureJitEnabled(); } ... } ... } } 注释1处获取要绑定的Service 。注释2处的BindServiceData的成员变量rebind的值为false，这样会调用注释3处的代码来调用Service的onBind方法，这样Service处于绑定状态了。如果rebind的值为true就会调用注释5处的Service的onRebind方法，结合前文的bindServiceLocked方法的注释4处，我们得知如果当前应用程序进程的Client端第一次与Service进行绑定，并且Service已经调用过onUnBind方法，则会调用Service的onRebind方法。
接着查看注释4的代码，实际上是调用AMS的publishService方法。讲到这，先给出这一部分的代码时序图（不包括Service启动过程）绘图2_副本.png我们接着来查看AMS的publishService方法，代码如下所示。
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java public void publishService(IBinder token, Intent intent, IBinder service) { ... synchronized(this) { if (!(token instanceof ServiceRecord)) { throw new IllegalArgumentException("Invalid service token"); } mServices.publishServiceLocked((ServiceRecord)token, intent, service); }} publishService方法中，调用了ActiveServices类型的mServices对象的publishServiceLocked方法：
frameworks/base/services/core/java/com/android/server/am/ActiveServices.java void publishServiceLocked(ServiceRecord r, Intent intent, IBinder service) { final long origId = Binder.clearCallingIdentity(); try { ... for (int conni=r.connections.size()-1; conni>=0; conni--) { ArrayList clist = r.connections.valueAt(conni); for (int i=0; i 注释1处的代码，我在前面介绍过，c.conn指的是IServiceConnection，它的具体实现为ServiceDispatcher.InnerConnection，其中ServiceDispatcher是LoadedApk的内部类，ServiceDispatcher.InnerConnectiond的connected方法的代码如下所示。
frameworks/base/core/java/android/app/LoadedApk.java static final class ServiceDispatcher { ... private static class InnerConnection extends IServiceConnection.Stub { final WeakReference mDispatcher; InnerConnection(LoadedApk.ServiceDispatcher sd) { mDispatcher = new WeakReference (sd); } public void connected(ComponentName name, IBinder service) throws RemoteException { LoadedApk.ServiceDispatcher sd = mDispatcher.get(); if (sd != null) { sd.connected(name, service);//1 } } } ... } 在注释1处调用了ServiceDispatcher 类型的sd对象的connected方法，代码如下所示。
frameworks/base/core/java/android/app/LoadedApk.java public void connected(ComponentName name, IBinder service) { if (mActivityThread != null) { mActivityThread.post(new RunConnection(name, service, 0));//1 } else { doConnected(name, service); } } 注释1处调用Handler类型的对象mActivityThread的post方法，mActivityThread实际上指向的是H。因此，通过调用H的post方法将RunConnection对象的内容运行在主线程中。RunConnection的定义如下所示。
frameworks/base/core/java/android/app/LoadedApk.java private final class RunConnection implements Runnable { RunConnection(ComponentName name, IBinder service, int command) { mName = name; mService = service; mCommand = command; } public void run() { if (mCommand == 0) { doConnected(mName, mService); } else if (mCommand == 1) { doDeath(mName, mService); } } final ComponentName mName; final IBinder mService; final int mCommand; } 在RunConnection的run方法中调用了doConnected方法：
frameworks/base/core/java/android/app/LoadedApk.java public void doConnected(ComponentName name, IBinder service) { ... // If there was an old service, it is not disconnected. if (old != null) { mConnection.onServiceDisconnected(name); } // If there is a new service, it is now connected. if (service != null) { mConnection.onServiceConnected(name, service);//1 }} 在注释1处调用了ServiceConnection类型的对象mConnection的onServiceConnected方法，这样在客户端中实现了ServiceConnection接口的类的onServiceConnected方法就会被执行。至此，Service的绑定过程就分析到这。
最后给出剩余部分的代码时序图。