广播介绍
Android中广播主要分为:有序广播、无序广播、粘性广播、局部广播。当然粘性广播也可以分为有序粘性广播和无序粘性广播,在这里我们探讨一下有序广播和无序广播。
· 普通广播(Normal Broadcast):用sendBroadcast()方法发送。
普通广播是完全异步的,逻辑上可以在同一时刻被所有匹配的接受者接收到,消息传递效率高,缺点是接受者不能将处理结果传递给下一个接收者,也无法终止广播传播。
· 有序广播(Ordered Broadcast):用sendOrderedBroadcast()方法发送。
有序广播的接收者们将按照事先生命的优先级依次接收,数越大优先级越高(取值范围:-1000~1000),优先级可以声明 在<intent-filter android:priority="n".../>,也可以调用IntentFilter对象的setPriority设置。并且接收者可以终止 传播(调用abortBroadcast()方法即可终止),一旦终止后面接收者就无法接受广播。另外,接受者可以将处理结果存入数据(可通过 setResultExtras(Bundle)方法将数据存入Broadcast),当做Broadcast再传递给下一级接收者(可通过代码 Bundle bundle = getResultExtras(true)获取上一级传递过来的数据)。
一、动态广播优先级
②无序广播以并行或者无序方式发送,无优先级
③有序广播按照串行方式发送,有优先级
二、静态广播优先级
①无序广播并行或者无序发送
②有序广播串行方式执行,如果是同等优先级,按照app安装的先后执行,因为静态广播注册到系统中,由PMS管理。
三、静态广播与动态广播的优先级
①对于无序广播,动态广播优先发送
②对于有序广播,动态广播和静态广播按照优先级合并之后发送,此外,如果优先级相同(算法决定),那么依然是动态态广播先接收
四、核心源码分析
ActivityManager.java
// Figure out who all will receive this broadcast. List receivers = null; //动态+静态广播 List<BroadcastFilter> registeredReceivers = null; //动态广播 // Need to resolve the intent to interested receivers... if ((intent.getFlags()&Intent.FLAG_RECEIVER_REGISTERED_ONLY) == 0) { receivers = collectReceiverComponents(intent, resolvedType, callingUid, users); } if (intent.getComponent() == null) { if (userId == UserHandle.USER_ALL && callingUid == Process.SHELL_UID) { // Query one target user at a time, excluding shell-restricted users UserManagerService ums = getUserManagerLocked(); for (int i = 0; i < users.length; i++) { if (ums.hasUserRestriction( UserManager.DISALLOW_DEBUGGING_FEATURES, users[i])) { continue; } List<BroadcastFilter> registeredReceiversForUser = mReceiverResolver.queryIntent(intent, resolvedType, false, users[i]); if (registeredReceivers == null) { registeredReceivers = registeredReceiversForUser; } else if (registeredReceiversForUser != null) { registeredReceivers.addAll(registeredReceiversForUser); } } } else { registeredReceivers = mReceiverResolver.queryIntent(intent, resolvedType, false, userId); } } final boolean replacePending = (intent.getFlags()&Intent.FLAG_RECEIVER_REPLACE_PENDING) != 0; if (DEBUG_BROADCAST) Slog.v(TAG, "Enqueing broadcast: " + intent.getAction() + " replacePending=" + replacePending); int NR = registeredReceivers != null ? registeredReceivers.size() : 0; if (!ordered && NR > 0) { // If we are not serializing this broadcast, then send the // registered receivers separately so they don't wait for the // components to be launched. final BroadcastQueue queue = broadcastQueueForIntent(intent); BroadcastRecord r = new BroadcastRecord(queue, intent, callerApp, callerPackage, callingPid, callingUid, resolvedType, requiredPermission, appOp, registeredReceivers, resultTo, resultCode, resultData, map, ordered, sticky, false, userId); if (DEBUG_BROADCAST) Slog.v( TAG, "Enqueueing parallel broadcast " + r); final boolean replaced = replacePending && queue.replaceParallelBroadcastLocked(r); if (!replaced) { queue.enqueueParallelBroadcastLocked(r); queue.scheduleBroadcastsLocked(); } registeredReceivers = null; NR = 0; } // Merge into one list. int ir = 0; if (receivers != null) { // A special case for PACKAGE_ADDED: do not allow the package // being added to see this broadcast. This prevents them from // using this as a back door to get run as soon as they are // installed. Maybe in the future we want to have a special install // broadcast or such for apps, but we'd like to deliberately make // this decision. String skipPackages[] = null; if (Intent.ACTION_PACKAGE_ADDED.equals(intent.getAction()) || Intent.ACTION_PACKAGE_RESTARTED.equals(intent.getAction()) || Intent.ACTION_PACKAGE_DATA_CLEARED.equals(intent.getAction())) { Uri data = intent.getData(); if (data != null) { String pkgName = data.getSchemeSpecificPart(); if (pkgName != null) { skipPackages = new String[] { pkgName }; } } } else if (Intent.ACTION_EXTERNAL_APPLICATIONS_AVAILABLE.equals(intent.getAction())) { skipPackages = intent.getStringArrayExtra(Intent.EXTRA_CHANGED_PACKAGE_LIST); } if (skipPackages != null && (skipPackages.length > 0)) { for (String skipPackage : skipPackages) { if (skipPackage != null) { int NT = receivers.size(); for (int it=0; it<NT; it++) { ResolveInfo curt = (ResolveInfo)receivers.get(it); if (curt.activityInfo.packageName.equals(skipPackage)) { receivers.remove(it); it--; NT--; } } } } } int NT = receivers != null ? receivers.size() : 0; int it = 0; ResolveInfo curt = null; BroadcastFilter curr = null; while (it < NT && ir < NR) { if (curt == null) { curt = (ResolveInfo)receivers.get(it); } if (curr == null) { curr = registeredReceivers.get(ir); } if (curr.getPriority() >= curt.priority) { // 优先级相同,把动态插入到静态前面 receivers.add(it, curr); ir++; curr = null; it++; NT++; } else { // Skip to the next ResolveInfo in the final list. it++; curt = null; } } } while (ir < NR) { if (receivers == null) { receivers = new ArrayList(); } receivers.add(registeredReceivers.get(ir)); ir++; } if ((receivers != null && receivers.size() > 0) || resultTo != null) { BroadcastQueue queue = broadcastQueueForIntent(intent); BroadcastRecord r = new BroadcastRecord(queue, intent, callerApp, callerPackage, callingPid, callingUid, resolvedType, requiredPermission, appOp, receivers, resultTo, resultCode, resultData, map, ordered, sticky, false, userId); if (DEBUG_BROADCAST) Slog.v( TAG, "Enqueueing ordered broadcast " + r + ": prev had " + queue.mOrderedBroadcasts.size()); if (DEBUG_BROADCAST) { int seq = r.intent.getIntExtra("seq", -1); Slog.i(TAG, "Enqueueing broadcast " + r.intent.getAction() + " seq=" + seq); } boolean replaced = replacePending && queue.replaceOrderedBroadcastLocked(r); if (!replaced) { queue.enqueueOrderedBroadcastLocked(r); queue.scheduleBroadcastsLocked(); } } return ActivityManager.BROADCAST_SUCCESS;