展开说说：Android服务之bindService解析

前面两篇文章我们分别总结了Android四种Service的基本使用以及源码层面总结一下startService的执行过程，本篇继续从源码层面总结bindService的执行过程。

本文依然按着是什么？有什么？怎么用？啥原理？的步骤来分析。

bindService使用方法和调用流程都与startService时有很多相似之处，方便的话请先阅读上一篇《展开说说：Android服务之startService解析》。

1. 是什么

调用bindService()来创建，调用方可以通过一个IBinder接口和service进行通信，需要通过ServiceConnection建立连接。多用于有交互的场景。

只能调用方通过unbindService()方法来断开连接。调用方可以和Service通讯，并且一个service可以同时和多个调用方存在绑定关系，解除绑定也需要所有调用全部解除绑定之后系统才会销毁service。

2、有什么

Service和Activity一样也有自己的生命周期，也需要在AndroidManifest.xml中注册。另外bindService的使用比startService要复杂一些：第一需要中创建一个Binder子类并定义方法来给使用者调用在onBind方法中返回它的实例；第二使用者需要创建ServiceConnection对象，并在onServiceConnected回调方法调用Binder子类中定义方法。

2.1 在AndroidManifest.xml中注册

和startService注册流程一样：

 <service android:name="com.example.testdemo.service.ServiceJia" />

2.2 bindService时Service的生命周期

与startService时执行的生命周期有些不同。

onCreate   

它只在Service刚被创建的时刻被调用，Service在运行中，这个方法将不会被调用。也就是只有经历过onDestroy生命周期以后再次。

onBind

当另一个组件调用 bindService()想要与Service绑定（例如执行 RPC）时执行，在此方法的实现中，必须通过返回 IBinder 提供一个接口，供客户端用来与服务通信。您必须始终实现此方法；但是，如果您不想允许绑定，则应返回 null。这个方法默认时返回null。

onUnbind

调用方调用 unbindService() 来解除Service绑定时执行。

onDestroy

所有绑定到Service的调用方都解绑以后，则系统会销毁该服务。

onRebind

当Service中的onUnbind方法返回true,并且Service调用unbindService之后并没有销毁,此时重新绑定时将会触发onRebind。Service执行过onBind又onUnbind返回true并且还没执行onDestroy，等再次bindService就会执行它。

日志打印

bindService
2024-12-01 11:19:14.434 30802-30802/com.example.testdemo3 E/com.example.testdemo3.service.ServiceJia: onCreate:

2023-12-01 11:19:14.436 30802-30802/com.example.testdemo3 E/com.example.testdemo3.activity.ServiceActivity: onServiceConnected:

2023-12-01 11:19:14.436 30802-30802/com.example.testdemo3 E/com.example.testdemo3.service.ServiceJia: JiaBinder  --doSomething: start conncetion    //这里不是生命周期，是binder对象调用binder内方法的打印，证明完成交互

unbindService
2023-12-01 11:21:10.705 12765-12765/com.example.testdemo3 E/com.example.testdemo3.service.ServiceJia: onUnbind:

2023-12-01 11:21:10.705 12765-12765/com.example.testdemo3 E/com.example.testdemo3.service.ServiceJia: onDestroy:

1. 怎么用

因为是有交互的嘛，因此肯定比那些启动以后就成了甩手掌柜的startService使用稍微负责一些，第一需要中创建一个Binder子类并定义方法来给使用者调用在onBind方法中返回它的实例；第二使用者需要创建ServiceConnection对象，并在onServiceConnected回调方法调用Binder子类中定义方法。

具体可以参考前面的《展开说说：Android四大组件之Service使用》已经总结了使用方法，这里不在赘述。

1. 啥原理，SDK版本API 30

bindService调用流程都与startService时有很多相似之处，方便的话请先阅读上一篇《展开说说：Android服务之startService解析》。

bindService的启动方法是调用

Intent serviceIntent = new Intent(ServiceActivity.this, ServiceJia.class);
bindService(serviceIntent,serviceConnection, Context.BIND_AUTO_CREATE)

然后我们顺着bindService方法开始解析源码，Go ：

4.1 从ContexWrapper的bindService开始，同startService：

@Override
public boolean bindService(Intent service, ServiceConnection conn,int flags) {return mBase.bindService(service, conn, flags);
}

4.2 ContextImpl类bindService

mBase的类型是Context，但实际代码逻辑是在它的实现类ContextImpl类。

 @Overridepublic boolean bindService(Intent service, ServiceConnection conn, int flags) {warnIfCallingFromSystemProcess();return bindServiceCommon(service, conn, flags, null, mMainThread.getHandler(), null,getUser());
}private boolean bindServiceCommon(Intent service, ServiceConnection conn, int flags,String instanceName, Handler handler, Executor executor, UserHandle user) {// Keep this in sync with DevicePolicyManager.bindDeviceAdminServiceAsUser.IServiceConnection sd;if (conn == null) {throw new IllegalArgumentException("connection is null");}if (handler != null && executor != null) {throw new IllegalArgumentException("Handler and Executor both supplied");}if (mPackageInfo != null) {if (executor != null) {sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(), executor, flags);} else {sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(), handler, flags);}} else {throw new RuntimeException("Not supported in system context");}validateServiceIntent(service);try {IBinder token = getActivityToken();if (token == null && (flags&BIND_AUTO_CREATE) == 0 && mPackageInfo != null&& mPackageInfo.getApplicationInfo().targetSdkVersion< android.os.Build.VERSION_CODES.ICE_CREAM_SANDWICH) {flags |= BIND_WAIVE_PRIORITY;}service.prepareToLeaveProcess(this);int res = ActivityManager.getService().bindIsolatedService(mMainThread.getApplicationThread(), getActivityToken(), service,service.resolveTypeIfNeeded(getContentResolver()),sd, flags, instanceName, getOpPackageName(), user.getIdentifier());if (res < 0) {throw new SecurityException("Not allowed to bind to service " + service);}return res != 0;} catch (RemoteException e) {throw e.rethrowFromSystemServer();}}

bindService调用bindServiceCommon方法。将ServiceConnection 转为Binder的实现类IServiceConnection方便跨进程的远程服务的回调自己定义的方法。

4.3 来到LoadedApk

 final @NonNull LoadedApk mPackageInfo;

因此来到LoadedApk 查看getServiceDispatcher方法：

@UnsupportedAppUsage
public final IServiceConnection getServiceDispatcher(ServiceConnection c,Context context, Handler handler, int flags) {return getServiceDispatcherCommon(c, context, handler, null, flags);
}private IServiceConnection getServiceDispatcherCommon(ServiceConnection c,Context context, Handler handler, Executor executor, int flags) {synchronized (mServices) {LoadedApk.ServiceDispatcher sd = null;ArrayMap<ServiceConnection, LoadedApk.ServiceDispatcher> map = mServices.get(context);if (map != null) {if (DEBUG) Slog.d(TAG, "Returning existing dispatcher " + sd + " for conn " + c);sd = map.get(c);}if (sd == null) {if (executor != null) {sd = new ServiceDispatcher(c, context, executor, flags);} else {sd = new ServiceDispatcher(c, context, handler, flags);}if (DEBUG) Slog.d(TAG, "Creating new dispatcher " + sd + " for conn " + c);if (map == null) {map = new ArrayMap<>();mServices.put(context, map);}map.put(c, sd);} else {sd.validate(context, handler, executor);}return sd.getIServiceConnection();}
}

private final ArrayMap<Context, ArrayMap<ServiceConnection, LoadedApk.ServiceDispatcher>> mServices
    = new ArrayMap<>();

mServices记录了应用当前活动的ServiceConnection和ServiceDispatcher的映射关系，不知是否记得ActivityThread中也有一个final ArrayMap<IBinder, Service> mServices = new ArrayMap<>(); 记录了IBinder,和Service的映射关系。

继续说LoadedApk中的service哈，上面代码会判断是否存在相同的ServiceConnection，如果不存在就创建新ServiceDispatcher实例并将其存储在mService中，key时ServiceConnection，value为ServiceDispatcher，ServiceDispatcher内部存储了ServiceConnection和InnerConnection对象。在调用bindService以后Service和调用方成功建立连接时系统会通过InnerConnection调用ServiceConnection中的onServiceConnected方法，此时我们就可以利用传过来的IBinder调用Service中的方法完成交互了。这个过程支持跨进程IPC通信，比如两个进程使用AIDL通信。

4.4 ContextImpl类bindService的bindIsolatedService

返回头看上面4.2中的bindService方法，继续向下看会调用ActivityManagerService的bindIsolatedService方法：

synchronized(this) {return mServices.bindServiceLocked(caller, token, service,resolvedType, connection, flags, instanceName, callingPackage, userId);}

4.5 来到ActiveService类的bindServiceLocked

继续调用本类的bringUpServiceLocked：

bringUpServiceLocked(serviceRecord,
        serviceIntent.getFlags(),
        callerFg, false, false);

在调用本类realStartServiceLocked：

realStartServiceLocked(r, app, execInFg);

一般来说源码中当一个方法多次穿梭调用之后突然带上了real，那一定是离真相不远了。

app.thread.scheduleCreateService(r, r.serviceInfo,
        mAm.compatibilityInfoForPackage(r.serviceInfo.applicationInfo),
        app.getReportedProcState());

这一行就很熟悉了，和上一篇startService一样，调用的ApplicationThread来创建Service实例并调用它的onCreate生命周期。

上一篇分析这个方法之下是调用onStartCommand生命周期

，没错这里也不例外下面requestServiceBindingsLocked(r, execInFg)也会去调用ApplicationThread的scheduleBindService：

r.app.thread.scheduleBindService(r, i.intent.getIntent(), rebind,
        r.app.getReportedProcState());

4.6来到ApplicationThread

利用它封装的handler发送BIND_SERVICE消息：

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);}

接收消息：

case BIND_SERVICE:Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceBind");handleBindService((BindServiceData)msg.obj);Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);break;

关键来咯：

 private void handleBindService(BindServiceData data) {Service s = mServices.get(data.token);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) {IBinder binder = s.onBind(data.intent);ActivityManager.getService().publishService(data.token, data.intent, binder);} else {s.onRebind(data.intent);ActivityManager.getService().serviceDoneExecuting(data.token, SERVICE_DONE_EXECUTING_ANON, 0, 0);}} catch (RemoteException ex) {throw ex.rethrowFromSystemServer();}} catch (Exception e) {if (!mInstrumentation.onException(s, e)) {throw new RuntimeException("Unable to bind to service " + s+ " with " + data.intent + ": " + e.toString(), e);}}}
}

上面代码显示根据token获取Service对象，然后判断首次绑定就调用onBind生命周期，已经绑定过就调用onReBind生命周期，返回的IBinder对象就可以用来调用Service中的方法了。但是为了让调用方拿到这个IBinder就同过onServiceConnected方法回调回去，这个工作就有ActivityManagerService的publishService方法来完成。

4.6 来到ActivityManagerService

 public void publishService(IBinder token, Intent intent, IBinder service) {// Refuse possible leaked file descriptorsif (intent != null && intent.hasFileDescriptors() == true) {throw new IllegalArgumentException("File descriptors passed in Intent");}synchronized(this) {if (!(token instanceof ServiceRecord)) {throw new IllegalArgumentException("Invalid service token");}mServices.publishServiceLocked((ServiceRecord)token, intent, service);}}

然后它有调用了ActiveService的publishServiceLocked方法来处理：

void publishServiceLocked(ServiceRecord r, Intent intent, IBinder service) {final long origId = Binder.clearCallingIdentity();try {if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "PUBLISHING " + r+ " " + intent + ": " + service);if (r != null) {Intent.FilterComparison filter= new Intent.FilterComparison(intent);IntentBindRecord b = r.bindings.get(filter);if (b != null && !b.received) {b.binder = service;b.requested = true;b.received = true;ArrayMap<IBinder, ArrayList<ConnectionRecord>> connections = r.getConnections();for (int conni = connections.size() - 1; conni >= 0; conni--) {ArrayList<ConnectionRecord> clist = connections.valueAt(conni);for (int i=0; i<clist.size(); i++) {ConnectionRecord c = clist.get(i);if (!filter.equals(c.binding.intent.intent)) {if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "Not publishing to: " + c);if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "Bound intent: " + c.binding.intent.intent);if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "Published intent: " + intent);continue;}if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "Publishing to: " + c);try {c.conn.connected(r.name, service, false);} catch (Exception e) {Slog.w(TAG, "Failure sending service " + r.shortInstanceName+ " to connection " + c.conn.asBinder()+ " (in " + c.binding.client.processName + ")", e);}}}}serviceDoneExecutingLocked(r, mDestroyingServices.contains(r), false);}} finally {Binder.restoreCallingIdentity(origId);}
}

它在for循环里调用一行代码：

c.conn.connected(r.name, service, false);

顺着代码看：

Conn的类型是是在ConnectionRecord类定义的IServiceConnection：

final IServiceConnection conn;  // The client connection.

Service就是建立连接的Ibinder实例。

4.7再次来到LoadedApk类

看一下IServiceConnection类connected方法：

private static class InnerConnection extends IServiceConnection.Stub {@UnsupportedAppUsagefinal WeakReference<LoadedApk.ServiceDispatcher> mDispatcher;InnerConnection(LoadedApk.ServiceDispatcher sd) {mDispatcher = new WeakReference<LoadedApk.ServiceDispatcher>(sd);}public void connected(ComponentName name, IBinder service, boolean dead)throws RemoteException {LoadedApk.ServiceDispatcher sd = mDispatcher.get();if (sd != null) {sd.connected(name, service, dead);}}
}

而它又调用了ActivityThread类，mActivityThread就是其中Handler子类 H ，这一步就是为了利用Handler在主线程回调给调用方的onServiceConnected：

public void connected(ComponentName name, IBinder service, boolean dead) {if (mActivityExecutor != null) {mActivityExecutor.execute(new RunConnection(name, service, 0, dead));} else if (mActivityThread != null) {mActivityThread.post(new RunConnection(name, service, 0, dead));} else {doConnected(name, service, dead);}
}

RunConnection 的实现：

private final class RunConnection implements Runnable {RunConnection(ComponentName name, IBinder service, int command, boolean dead) {mName = name;mService = service;mCommand = command;mDead = dead;}public void run() {if (mCommand == 0) {doConnected(mName, mService, mDead);} else if (mCommand == 1) {doDeath(mName, mService);}}final ComponentName mName;final IBinder mService;final int mCommand;final boolean mDead;
}

回调onServiceConnected，彻底呼应上了：

public void doConnected(ComponentName name, IBinder service, boolean dead) {ServiceDispatcher.ConnectionInfo old;ServiceDispatcher.ConnectionInfo info;synchronized (this) {if (mForgotten) {// We unbound before receiving the connection; ignore// any connection received.return;}old = mActiveConnections.get(name);if (old != null && old.binder == service) {// Huh, already have this one.  Oh well!return;}if (service != null) {// A new service is being connected... set it all up.info = new ConnectionInfo();info.binder = service;info.deathMonitor = new DeathMonitor(name, service);try {service.linkToDeath(info.deathMonitor, 0);mActiveConnections.put(name, info);} catch (RemoteException e) {// This service was dead before we got it...  just// don't do anything with it.mActiveConnections.remove(name);return;}} else {// The named service is being disconnected... clean up.mActiveConnections.remove(name);}if (old != null) {old.binder.unlinkToDeath(old.deathMonitor, 0);}}// If there was an old service, it is now disconnected.if (old != null) {mConnection.onServiceDisconnected(name);}if (dead) {mConnection.onBindingDied(name);}// If there is a new viable service, it is now connected.if (service != null) {mConnection.onServiceConnected(name, service);} else {// The binding machinery worked, but the remote returned null from onBind().mConnection.onNullBinding(name);}
}

至此bindService的绑定流程分析完毕！

才疏学浅，如有错误，欢迎指正，多谢。