private Intent registerReceiverInternal(BroadcastReceiver receiver, int userId,
            IntentFilter filter, String broadcastPermission,
            Handler scheduler, Context context, int flags) {
        IIntentReceiver rd = null;
        if (receiver != null) {
            if (mPackageInfo != null && context != null) {
                if (scheduler == null) {
                    // 注冊(cè)receiver的時(shí)候可以指定接受recover的Handler
                    // 如果沒(méi)有指定，則默認(rèn)用主線程的handler處理
                    scheduler = mMainThread.getHandler();
                }
                // 獲取IIntentReceiver
                // 這個(gè)是一個(gè)Binder對(duì)象，當(dāng)廣播來(lái)臨時(shí)，用于AMS向客戶端發(fā)起回調(diào)
                rd = mPackageInfo.getReceiverDispatcher(
                    receiver, context, scheduler,
                    mMainThread.getInstrumentation(), true);
            } else {
                if (scheduler == null) {
                    scheduler = mMainThread.getHandler();
                }
                rd = new LoadedApk.ReceiverDispatcher(
                        receiver, context, scheduler, null, true).getIIntentReceiver();
            }
        }
        try {
            // binder call至AMS，進(jìn)行廣播注冊(cè)
            final Intent intent = ActivityManager.getService().registerReceiver(
                    mMainThread.getApplicationThread(), mBasePackageName, rd, filter,
                    broadcastPermission, userId, flags);
            if (intent != null) {
                intent.setExtrasClassLoader(getClassLoader());
                intent.prepareToEnterProcess();
            }
            return intent;
        } catch (RemoteException e) {
            throw e.rethrowFromSystemServer();
        }
    }

    public IIntentReceiver getReceiverDispatcher(BroadcastReceiver r,
            Context context, Handler handler,
            Instrumentation instrumentation, boolean registered) {
        synchronized (mReceivers) {
            // 如果Context相同，每個(gè)receiver對(duì)應(yīng)一個(gè)ReceiverDispatcher
            LoadedApk.ReceiverDispatcher rd = null;
            ArrayMap<BroadcastReceiver, LoadedApk.ReceiverDispatcher> map = null;
            if (registered) {
                map = mReceivers.get(context);
                if (map != null) {
                    rd = map.get(r);
                }
            }
            if (rd == null) {
                rd = new ReceiverDispatcher(r, context, handler,
                        instrumentation, registered);
                if (registered) {
                    if (map == null) {
                        map = new ArrayMap<BroadcastReceiver, LoadedApk.ReceiverDispatcher>();
                        mReceivers.put(context, map);
                    }
                    map.put(r, rd);
                }
            } else {
                rd.validate(context, handler);
            }
            rd.mForgotten = false;
            return rd.getIIntentReceiver();
        }
    }

    static final class ReceiverDispatcher {
        // 是一個(gè)binder對(duì)象
        final static class InnerReceiver extends IIntentReceiver.Stub {
            final WeakReference<LoadedApk.ReceiverDispatcher> mDispatcher;
            final LoadedApk.ReceiverDispatcher mStrongRef;

            InnerReceiver(LoadedApk.ReceiverDispatcher rd, boolean strong) {
                mDispatcher = new WeakReference<LoadedApk.ReceiverDispatcher>(rd);
                mStrongRef = strong ? rd : null;
            }

            @Override
            public void performReceive(Intent intent, int resultCode, String data,
                    Bundle extras, boolean ordered, boolean sticky, int sendingUser) {
                    // 這里就是廣播真正派發(fā)到本進(jìn)程的時(shí)候從systemserver binder call過(guò)來(lái)執(zhí)行的
                ...
        }

        final IIntentReceiver.Stub mIIntentReceiver;
        final BroadcastReceiver mReceiver;
        final Context mContext;
        final Handler mActivityThread;
        final Instrumentation mInstrumentation;
        final boolean mRegistered;
        final IntentReceiverLeaked mLocation;
        RuntimeException mUnregisterLocation;
        boolean mForgotten;
        ...
    }

    public Intent registerReceiver(IApplicationThread caller, String callerPackage,
            IIntentReceiver receiver, IntentFilter filter, String permission, int userId,
            int flags) {
        enforceNotIsolatedCaller("registerReceiver");
        ArrayList<Intent> stickyIntents = null;
        ProcessRecord callerApp = null;
        final boolean visibleToInstantApps
                = (flags & Context.RECEIVER_VISIBLE_TO_INSTANT_APPS) != 0;
        int callingUid;
        int callingPid;
        boolean instantApp;
        synchronized(this) {
            if (caller != null) {
                // 正常來(lái)講caller是發(fā)起binder call的客戶端進(jìn)程對(duì)應(yīng)的ApplicationThread對(duì)象
                // 如果為null則拋異常
                callerApp = getRecordForAppLocked(caller);
                if (callerApp == null) {
                    throw new SecurityException(
                            "Unable to find app for caller " + caller
                            + " (pid=" + Binder.getCallingPid()
                            + ") when registering receiver " + receiver);
                }
                if (callerApp.info.uid != SYSTEM_UID &&
                        !callerApp.pkgList.containsKey(callerPackage) &&
                        !"android".equals(callerPackage)) {
                    throw new SecurityException("Given caller package " + callerPackage
                            + " is not running in process " + callerApp);
                }
                callingUid = callerApp.info.uid;
                callingPid = callerApp.pid;
            } else {
                callerPackage = null;
                callingUid = Binder.getCallingUid();
                callingPid = Binder.getCallingPid();
            }

            // 判斷caller是否為instant app
            instantApp = isInstantApp(callerApp, callerPackage, callingUid);
            userId = mUserController.handleIncomingUser(callingPid, callingUid, userId, true,
                    ALLOW_FULL_ONLY, "registerReceiver", callerPackage);

            // 獲取廣播注冊(cè)的filter中的action封裝到list中
            Iterator<String> actions = filter.actionsIterator();
            if (actions == null) {
                ArrayList<String> noAction = new ArrayList<String>(1);
                noAction.add(null);
                actions = noAction.iterator();
            }

            // mStickyBroadcasts是一個(gè)二級(jí)map
            // 一級(jí)key是userId，二級(jí)key是廣播對(duì)應(yīng)的action，value是廣播對(duì)應(yīng)intent的list（一般只有一個(gè)intent）
            // 這里是為了查詢對(duì)于當(dāng)前user，本次注冊(cè)的所有action對(duì)應(yīng)的sticky廣播的intent
            int[] userIds = { UserHandle.USER_ALL, UserHandle.getUserId(callingUid) };
            while (actions.hasNext()) {
                String action = actions.next();
                for (int id : userIds) {
                    ArrayMap<String, ArrayList<Intent>> stickies = mStickyBroadcasts.get(id);
                    if (stickies != null) {
                        ArrayList<Intent> intents = stickies.get(action);
                        if (intents != null) {
                            if (stickyIntents == null) {
                                stickyIntents = new ArrayList<Intent>();
                            }
                            stickyIntents.addAll(intents);
                        }
                    }
                }
            }
        }

        ArrayList<Intent> allSticky = null;
        // 這里不為null表示本次注冊(cè)的廣播中有sticky廣播
        if (stickyIntents != null) {
            final ContentResolver resolver = mContext.getContentResolver();
            // 查找匹配的sticky廣播
            for (int i = 0, N = stickyIntents.size(); i < N; i++) {
                Intent intent = stickyIntents.get(i);
                // 如果caller是instant app，且intent的flag不允許對(duì)instant可見(jiàn)，則跳過(guò)
                if (instantApp &&
                        (intent.getFlags() & Intent.FLAG_RECEIVER_VISIBLE_TO_INSTANT_APPS) == 0) {
                    continue;
                }
                // If intent has scheme "content", it will need to acccess
                // provider that needs to lock mProviderMap in ActivityThread
                // and also it may need to wait application response, so we
                // cannot lock ActivityManagerService here.
                if (filter.match(resolver, intent, true, TAG) >= 0) {
                    if (allSticky == null) {
                        allSticky = new ArrayList<Intent>();
                    }
                    allSticky.add(intent);
                }
            }
        }

        // 直接把最近的一個(gè)匹配到的sticky廣播返回
        Intent sticky = allSticky != null ? allSticky.get(0) : null;
        // 廣播注冊(cè)的時(shí)候receiver是可以為null的，這種情況下這里直接return
        if (receiver == null) {
            return sticky;
        }

        synchronized (this) {
            // 校驗(yàn)caller進(jìn)程是否正常
            if (callerApp != null && (callerApp.thread == null
                    || callerApp.thread.asBinder() != caller.asBinder())) {
                // Original caller already died
                return null;
            }
            // mRegisteredReceivers中存放了所有的已注冊(cè)的receiver
            // 每個(gè)BroadcastReceiver對(duì)應(yīng)一個(gè)InnerReceiver，即Binder對(duì)象
            // binder對(duì)象做key，value是ReceiverList
            // ReceiverList是一個(gè)ArrayList
            ReceiverList rl = mRegisteredReceivers.get(receiver.asBinder());
            if (rl == null) {
                rl = new ReceiverList(this, callerApp, callingPid, callingUid,
                        userId, receiver);
                if (rl.app != null) {
                    rl.app.receivers.add(rl);
                } else {
                    try {
                        // 如果是新創(chuàng)建的receiver，還需要linkToDeath
                        receiver.asBinder().linkToDeath(rl, 0);
                    } catch (RemoteException e) {
                        return sticky;
                    }
                    rl.linkedToDeath = true;
                }
                // 放入mRegisteredReceivers
                mRegisteredReceivers.put(receiver.asBinder(), rl);
            } else if (rl.uid != callingUid) {
                throw new IllegalArgumentException(
                        "Receiver requested to register for uid " + callingUid
                        + " was previously registered for uid " + rl.uid
                        + " callerPackage is " + callerPackage);
            } else if (rl.pid != callingPid) {
                throw new IllegalArgumentException(
                        "Receiver requested to register for pid " + callingPid
                        + " was previously registered for pid " + rl.pid
                        + " callerPackage is " + callerPackage);
            } else if (rl.userId != userId) {
                throw new IllegalArgumentException(
                        "Receiver requested to register for user " + userId
                        + " was previously registered for user " + rl.userId
                        + " callerPackage is " + callerPackage);
            }
            // 每一個(gè)IntentFilter對(duì)應(yīng)一個(gè)BroadcastFilter
            BroadcastFilter bf = new BroadcastFilter(filter, rl, callerPackage,
                    permission, callingUid, userId, instantApp, visibleToInstantApps);
            // receiverList中存放了通過(guò)這個(gè)receiver注冊(cè)的所有的filter
            // 每調(diào)用一次register就會(huì)add一次
            rl.add(bf);
            // mReceiverResolver中存放所有的BroadcastFilter
            mReceiverResolver.addFilter(bf);

            // 有匹配的sticky廣播，則直接開(kāi)始調(diào)度派發(fā)
            if (allSticky != null) {
                ArrayList receivers = new ArrayList();
                receivers.add(bf);

                // 對(duì)于每一個(gè)sticky廣播，創(chuàng)建BroadcastRecord并入隊(duì)（并行）
                final int stickyCount = allSticky.size();
                for (int i = 0; i < stickyCount; i++) {
                    Intent intent = allSticky.get(i);
                    // 根據(jù)flag是否有FLAG_RECEIVER_FOREGROUND判斷入隊(duì)是前臺(tái)還是后臺(tái)隊(duì)列
                    BroadcastQueue queue = broadcastQueueForIntent(intent);
                    BroadcastRecord r = new BroadcastRecord(queue, intent, null,
                            null, -1, -1, false, null, null, AppOpsManager.OP_NONE, null, receivers,
                            null, 0, null, null, false, true, true, -1);
                    // 入隊(duì)，并行隊(duì)列
                    queue.enqueueParallelBroadcastLocked(r);
                    // 啟動(dòng)廣播的調(diào)度，也就是開(kāi)始派發(fā)廣播
                    queue.scheduleBroadcastsLocked();
                }
            }
            return sticky;
        }
    }