android4.4组件分析--service组件-bindService源代码分析

6.1.1.    bindService

由于有前面分析startService的代码实现过程，则对于bindService的代码分析就不用那么具体介绍，在介绍流程的同一时候更关注一些细节上的部分。

首先，bindService也是通过 ContextWrapper.bindService，再到ContextImpl的bindService，然后是bindServiceCommon，须要注意的是，传入的ServiceConnection被转换成IServiceConnection类型，

private boolean bindServiceCommon(Intent service,
ServiceConnection conn, int flags,

UserHandle user) {

IServiceConnection
sd;

…

sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(),

mMainThread.getHandler(), flags);

…

int res = ActivityManagerNative.getDefault().bindService(

mMainThread.getApplicationThread(), getActivityToken(),

service, service.resolveTypeIfNeeded(getContentResolver()),

sd, flags, user.getIdentifier());

}

接下去是进入AMS的bindService，再调用ActiveServices.java 的bindServiceLocked，它会把IServiceConnection实例存放到ConnectionRecord里面，并运行bringUpServiceLocked，

int bindServiceLocked(IApplicationThread caller, IBinder token,

Intent service, String resolvedType,

IServiceConnection connection, int flags, int userId) {

…

ConnectionRecord c = new ConnectionRecord(b, activity,

connection, flags, clientLabel, clientIntent);

IBinder binder = connection.asBinder();

if ((flags&Context.BIND_AUTO_CREATE) != 0) {

s.lastActivity = SystemClock.uptimeMillis();

if (bringUpServiceLocked(s, service.getFlags(), callerFg, false) != null){

return 0;

}

}

…

if (s.app != null && b.intent.received) {

// Service is already running, so we can immediately

// publish the connection.

try {

c.conn.connected(s.name, b.intent.binder);

} catch (Exception e) {

Slog.w(TAG, "Failure sending service " + s.shortName

+ " to connection " + c.conn.asBinder()

+ " (in " + c.binding.client.processName + ")", e);

}

// If this is the first app connected back to this binding,

// and the service had previously asked to be told when

// rebound, then do so.

if (b.intent.apps.size() == 1 && b.intent.doRebind) {

requestServiceBindingLocked(s, b.intent, callerFg, true);

}

} else if (!b.intent.requested) {

requestServiceBindingLocked(s, b.intent, callerFg, false);

}

}

依据之前的分析ServiceLocked会调用realStartServiceLocked，而realStartServiceLocked则先调用scheduleCreateService，完毕service的创建和Oncreate（）的运行，然后运行requestServiceBindingsLocked，这个是bind服务相关处理，最后是sendServiceArgsLocked，这个是Start服务的处理。

private final void realStartServiceLocked(ServiceRecord r,

ProcessRecord app, boolean execInFg) throws RemoteException {

…

app.thread.scheduleCreateService(r, r.serviceInfo,                    mAm.compatibilityInfoForPackageLocked(r.serviceInfo.applicationInfo),                 app.repProcState);

…

requestServiceBindingsLocked(r, execInFg);

sendServiceArgsLocked(r, execInFg, true);

…

}

requestServiceBindingsLocked再调用ActivityThread的方法scheduleBindService，在ActivityThread.java 中，它发出一个BIND_SERVICE事件，被handleBindService处理，

private void handleBindService(BindServiceData data) {

…

if (!data.rebind) {

IBinder binder = s.onBind(data.intent);

ActivityManagerNative.getDefault().publishService(

data.token, data.intent, binder);

} else {

s.onRebind(data.intent);

ActivityManagerNative.getDefault().serviceDoneExecuting(

data.token, 0, 0, 0);

}

…

这里先调用服务的onBind方法，由于服务是重载的，所以会运行详细服务类的方法，并返回服务里的binder实例，这个binder随后会被使用到，

当中AMS的publishService方法被调用，在 ActivityManagerService.java中又会调用   ActiveServices.java 的publishServiceLocked，

void publishServiceLocked(ServiceRecord r, Intent intent, IBinder service) {

…

for (int conni=r.connections.size()-1; conni>=0; conni--) {

ArrayList<ConnectionRecord> clist = r.connections.valueAt(conni);

for (int i=0; i<clist.size(); i++) {

ConnectionRecord c = clist.get(i);

…

try {

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

} …

serviceDoneExecutingLocked(r, mDestroyingServices.contains(r), false);

这里主要调用到c.conn.connected，c就是ConnectionRecord，其成员conn是一个IServiceConnection类型实例，这在前面有提到，connected则是事实上现类的方法。

对于IServiceConnection，它是一个接口，位置在(frameworks\base): core/java/android/app/IServiceConnection.aidl，aidl定义例如以下，它仅仅有一个接口方法connected，

oneway interface IServiceConnection {

void connected(in ComponentName name, IBinder service);

}

其服务端的实如今LoadedApk.java，例如以下，InnerConnection类是在ServiceDispatcher的内部类，并在ServiceDispatcher的构造函数里面实例化的，其方法connected也是调用的ServiceDispatcher的方法connected，

private static class InnerConnection extendsIServiceConnection.Stub {

final WeakReference<LoadedApk.ServiceDispatcher> mDispatcher;

InnerConnection(LoadedApk.ServiceDispatcher sd) {

mDispatcher = new WeakReference<LoadedApk.ServiceDispatcher>(sd);

}

public void connected(ComponentName name, IBinder service) throws RemoteException {

LoadedApk.ServiceDispatcher sd = mDispatcher.get();

if (sd != null) {

sd.connected(name, service);

}

}

}

ServiceDispatcher(ServiceConnection conn,

Context context, Handler activityThread, int flags) {

mIServiceConnection = new InnerConnection(this);

mConnection = conn;

mContext = context;

mActivityThread = activityThread;

mLocation = new ServiceConnectionLeaked(null);

mLocation.fillInStackTrace();

mFlags = flags;

}

这里就再回到我们前面的ContextImpl里面bindServiceCommon方法里面，这里进行ServiceConnection转化为IServiceConnection时，调用了mPackageInfo.getServiceDispatcher，mPackageInfo就是一个LoadedApk实例，

/*package*/ LoadedApk mPackageInfo;

private boolean bindServiceCommon(Intent service, ServiceConnection conn, int flags,

UserHandle user) {

IServiceConnection sd;

sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(),

mMainThread.getHandler(), flags);

}

所以，getServiceDispatcher会创建一个ServiceDispatcher实例，并将ServiceDispatcher实例和ServiceConnection实例形成KV对，并在ServiceDispatcher的构造函数里将ServiceConnection实例c赋值给ServiceConnection的成员变量mConnection，

public final IServiceConnection getServiceDispatcher(ServiceConnection c,

Context context, Handler handler, int flags) {

synchronized (mServices) {

LoadedApk.ServiceDispatcher sd = null;

ArrayMap<ServiceConnection, LoadedApk.ServiceDispatcher> map = mServices.get(context);

if (map != null) {

sd = map.get(c);

}

if (sd == null) {

sd = new ServiceDispatcher(c, context, handler, flags);

if (map == null) {

map = new ArrayMap<ServiceConnection, LoadedApk.ServiceDispatcher>();

mServices.put(context, map);

}

map.put(c, sd);

…

}

这样，在运行ServiceDispatcher的connected方法时，就会调用到ServiceConnection的

onServiceConnected，完毕绑定ServiceConnection的触发。

public void doConnected(ComponentName name, IBinder service) {

…

if (old != null) {

mConnection.onServiceDisconnected(name);

}

// If there is a new service, it is now connected.

if (service != null) {

mConnection.onServiceConnected(name, service);

}

}

至此，就运行完了bindService的主要过程。

我们以下用一张图来总结这个流程，