After reading this article, you will know the following:

• What is broadcast and its usage scenario
• Android broadcast classification
• Method of registration for broadcast
• Advantages and principles of local broadcasting
• Safety of broadcasting

1.1 What is BroadcastReceiver

• Is one of the four components, mainly used for receivingappTransmitted broadcast
• Internal communication mechanism: PassandroidOf the systemBinderMechanism.

1.2 Broadcast Classification

1.2.1 Out-of-order Broadcast

• Also known as standard broadcast, it is completely asynchronous

Broadcast execution.

• After a broadcast is sent, all broadcast receivers receive the broadcast message at almost the same time, without any order between them, which makes broadcasting more efficient.
• Advantages:Fully asynchronous, logically any receiver can receive the broadcast, high efficiency
• Disadvantages:The receiver cannot pass the processing to the next receiver and cannot terminate the broadcast.

1.2.2 Orderly Broadcast

• Is a synchronous broadcast.

• After a broadcast is sent, only one broadcast receiver can receive the broadcast message at any one time, and the broadcast receiver will continue transmission when its logic is complete.

• Call the SendOrderedBroadcast() method to send a broadcast, and abortBroadcast() method to intercept the broadcast. You can set the Android :property attribute in the
  
  tag to set the priority. If this attribute is not set, broadcasts are received in the order in which they are registered.
  

• Sequential broadcast receivers can transmit data to each other.

• When a broadcast receiver receives a broadcast, the current broadcast can also pass the data to the next receiver using the setResultData method.

• The getStringExtra function is used to get the original data of the broadcast. The getResultData method is used to get the data added by the last broadcast receiver. AbortBroadcast method is used to discard the broadcast, so that the broadcast is no longer received by other receivers.

• conclusion

1. Sequential transmission according to the priority of the recipientA > B > C ,
2. Each has the right to stop broadcasting, and the next one doesn’t
3. Each one can be modified, and the next one gets the result of the previous modification.

1.2.3 Ultimate broadcaster

• Context.sendOrderedBroadcast ( intent , receiverPermission , resultReceiver , scheduler , initialCode , initialData , initialExtras )When we can specifyresultReceiverIs the ultimate broadcast receiver.
• If the higher-priority recipient does not terminate the broadcast, hisonReceiveIt will be executed twice
• The first is normal reception
• The second is the final reception
• If the one with the highest priority terminates the broadcast, he still receives a final broadcast

1.2.4 Common Scenarios of Broadcast receivers

• Boot up,sdCard mounting, low battery, outgoing phone, lock screen, etc
• For example, according to the requirements of the product manager, design whether the lock screen decides to pause the music when playing the music.

1.3 Types of BroadcastReceiver

1.3.1 Broadcast as a communication mode between Android components, the following scenarios are used:

Expand on the previous section “Please describe BroadcastReceiver”

• APPInternal message communication.
• differentAPPMessage communication between.
• AndroidMessage communication between the system and APP under certain circumstances.
• Broadcast uses the observer pattern, a message-based publish/subscribe event model. Broadcast decouples the sender and receiver of broadcast to a great extent, making the system easy to integrate and expand.
• BroadcastReceiver is a global listener that monitors global broadcast messages and facilitates communication between different components in the system.
• Custom broadcast receivers need to inherit from the base classBroadcastReceiverAnd implement abstract methodsonReceive ( context, intent ). By default, broadcast receivers also run on the main thread, soonReceiver()Cannot perform time-consuming operations (no more than10s), otherwise will produceANRThe problem.onReceiver()You can use send when interacting with other components in a methodNotification, start,ServiceAnd so on, it is best not to startActivity.

1.3.2 System Broadcast

• AndroidMultiple system broadcasts are built into the system. As long as the basic operations of the mobile phone are involved, corresponding system broadcasts will be basically issued, such as startup, network state change, taking photos, screen closing and opening, power shortage, etc. Within the system, a system broadcast is automatically issued by the system when it occurs at a specific time.
• Common System BroadcastIntentIn theActionIs the following value:

1. SMS reminder:android.provider.Telephony.SMS_RECEIVED
2. Low battery:ACTION_BATIERY_LOW
3. Electric quantity changes:ACTION_BATTERY_CHANGED
4. Power connection:ACTION_POWER_CO             

• fromThe Android 7.0At first, the system will no longer send a broadcastACTION_NEW_PICTURE 和 ACTION_NEW_VIDEOFor broadcastingCONNECTIVITY_ACTIONMust be used in coderegisterReceiverMethod to register the receiver inAndroidManifestThe file states that the receiver does not work.
• fromThe Android 8.0Start, for most implicit broadcasts, cannot be inAndroidManifestThe receiver is declared in the file.

1.3.3 Local broadcast

• The sender and receiver of a local broadcast belong to the same entityAPP
• Compared with global broadcast, it has the following advantages:

1. The rest of theAPPNo local broadcast, no need to worry about data leakage.
2. otherAPPImpossible to presentAPPSend local broadcast, do not worry about security holes by othersAPPTo use.
3. Local broadcast is more efficient than global broadcast transmitted through the system.

• Android v4Provided in the packageLocalBroadcastManagerClass for unified handling of APP local broadcast, used in almost the same way as global broadcast, except to call the register/unregister broadcast receiver and send broadcast read method, need to passLocalBroadcastManagerOf the classgetInstance()Method to get an instance call.

1.4 Registration mode of BroadcastReceiver

1.4.1 Static Registration

In the androidmanifest.xml file.

<receiver android:name=".MyReceiver" android:exported="true"> <intent-filter> <! - specifies the BroadcastReceiver response by the Intent of the Action - > < Action android: name = "android. Intent. Action. INPUT_METHOD_CHANGED" <action android:name="android.intent.action.BOOT_COMPLETED" /> </intent-filter> </receiver>Copy the code

• There are two important attributes to focus on:

1. android: exportedIt sets thisBroadcastReceiverCan you accept otherAPPBroadcast, when set tofalseCan only accept components of the same application or have the sameuser IDThe message sent by the application. The default value for this property is set byBroadcastReceiverIn the presence ofIntent-filterDecided, if there isIntent-filter, the default value istrue, or forfalse 。
2. android: permissionIf this property is set, only broadcasts sent by broadcast senders with corresponding permissions can be sent by this propertyBroadcastReceiverAcceptable; If not set, this value grants permissions to the entire application.

1.4.2 Dynamic Registration

• callContext 的 registerReceiver ( BroadcastReceiver receiver , IntentFilter filter )Method specifies.

1.5 How to register and use BroadcastReceiver in Mainfest and code? (An action is the key)

1.5.1 Registering with a File (Static Broadcast)

• As long as the app is running, it will receive broadcast messages all the time

• Presentation:

1. aappCustom class inheritanceBroadcastReceiverAnd then ask me to rewrite itonReveivermethods

public class MyBroadCastReceiver extends BroadcastReceiver { @Override public void onReceive(Context context, Intent Intent) {log. d("MyBroadCastReceiver", "broadcastReceiver "," emsp; + intent.getStringExtra("info") + ""); }}Copy the code

2. The manifest file is registered and setAction“, simply completing the preparation for acceptance

<receiver android:name=".MyBroadCastReceiver">
    <intent-filter>
        <action android:name="myBroadcast.action.call"/>
    </intent-filter>
</receiver>
Copy the code

1.5.2 Code Registration (Dynamic Broadcast)

• Broadcasts cannot be received when the registered Activity or Service is destroyed.

• Presentation:

1. At the same time as the broadcast receiverappIn theMainActivityAdd a register button to register broadcast receivers
2. Set intent filtering, addAction

//onCreate Create broadcastReceiver object mReceiver = new MyBroadCastReceiver(); Public void click(View View) {IntentFilter IntentFilter = new IntentFilter(); intentFilter.addAction("myBroadcast.action.call"); registerReceiver(mReceiver, intentFilter); }Copy the code

3. Unregister while destroying

@Override
protected void onDestroy() {
    unregisterReceiver(mReceiver);
    super.onDestroy();
}
Copy the code

1.5.3 In another APP, define a button, set intention, Intention to add message content, Intention to set Action (…) To match, just send a broadcast.

public void click(View view) { Intent intent = new Intent(); Intent. PutExtra ("info", "message content "); intent.setAction("myBroadcast.action.call"); sendBroadcast(intent); }Copy the code

• Running twoappAfter:

1. Static registration method: anotherappI got it on the radio
2. Dynamic registration method: ownappFirst code registration, then anotherappJust broadcast it.

1.6 What is the implementation principle of BroadcastReceiver?

• Broadcasting in Android uses the observer pattern of design patterns: a message-based publish/subscribe event model.

• There are three main roles in the model:

1. Message subscriber (broadcast receiver)
2. Message Publisher (Broadcast publisher)
3. Message center (AMS, i.e.,Activity Manager Service ）

1.6.1 principle:

• Broadcast receiver throughBinderMechanism inAMS(Activity Manager Service) register;
• The broadcast sender passesBinderMechanism toAMSSend a broadcast;
• AMSAccording to the request of the broadcast sender, in the registered list, find the appropriateBroadcastReceiver(Look for evidence:IntentFilter / Permission);
• AMSSend the broadcast toBroadcastReceiverCorresponding message loop queue;
• The broadcast receiver gets the broadcast through the message loop and calls backonReceive()Methods.
• Note that the broadcast is sent and received asynchronously, and the sender does not care if or when the receiver is received.

1.7 Local Broadcast

• The local broadcast mechanism improves security by allowing outgoing broadcasts to be transmitted only within the application, and the broadcast receiver to accept only broadcasts from the application itself.
• Local broadcasting mainly uses oneLocalBroadcastManagerTo manage broadcasts, and provides methods for sending broadcasts and registering broadcast receivers.
• Developers just need to implement their ownBroadcastReceiverSubclass, rewriteonReceive ( Context context, Intetn intent )Method can.
• When other components passsendBroadcast() 、sendStickyBroadcast() 、sendOrderBroadcast()Method sends a broadcast message if theBroadcastReceiverAlso “interested” in the news,BroadcastReceiver 的 onReceive ( Context context, Intetn intent )The method will be fired.
• Use steps:

1. For instance call LocalBroadcastManager. GetInstance ()
2. Call the registerReceiver() method to register the broadcast
3. Call the sendBroadcast() method to send a broadcast
4. Call the unregisterReceiver() method to cancel registration

1.7.1 Precautions:

1. Local broadcasts cannot be accepted through static registration and are more efficient than system global broadcasts.
2. Start on the airActivityIs requiredIntentjoinFLAG_ACTIVITY_NEW_TASKFlag, otherwise an error is reported because a stack is required to hold the newly openedActivity 。
3. Pop up on broadcastAlertdialog“, you need to set the dialog box type toTYPE_SYSTEM_ALERTOtherwise, it cannot be ejected.
4. Don’t inonReceiver()Method to add too much logic or perform any time-consuming operations, since threads are not allowed to open in the broadcast receiver, whenonReceiver()When a method runs for a long time without ending, the program reports an error.

1.8 Sticky Broadcast Sticky Broadcast

• If the sender sends a broadcast and the Receiver registers his or her own Receiver after the broadcast is sent, then the Receiver cannot receive the broadcast
• To do thisAndroidThe introduction of theStickyBroadcast, the broadcast just sent will be saved after the broadcast is sent (Intent), so that when the recipient is finished registeringReceiverThen you can continue to use the broadcast.
• If multiple copies of the same are sent before the recipient’s registration is completedActionYou will only receive one sticky broadcast after registeringActionAnd the message is the last broadcast.
• A change in the network state of the system sends a broadcast that is called a sticky broadcast.

1. Viscous broadcast passageContext 的 sendStickyBroadcast ( Intent )Interface send, need to add permission
2. USES - the permission of the android: name = "android permission. BROADCAST_STICKY"
3. Also throughContext 的 removeStickyBroadcast ( Intent intent )Interface removes cached sticky broadcasts

1.9 LocalBroadcastManager,

1.9.1 features:

1. Broadcasts sent from it will only spread within your APP, so you don’t have to worry about leaking private data;
2. otherAPPCan’t do anything to youAPPSend this broadcast, because your APP can’t possibly receive this broadcast from a non-app, so you don’t have to worry about security vulnerabilities to exploit it;
3. More efficient than the global broadcast of the system.

1.9.2 Source code analysis:

1. LocalBroadcastManagerInternal collaboration mainly depends on these twoMapCollection:MReceivers 和 MActionsAnd, of course, a List collectionMPendingBroadcasts, this is mainly to store the broadcast object to be received.
2. LocalBroadcastManagerThe reason for the efficiency is mainly because it is internally throughHandlerRealized, itssendBroadcast()The meaning of the method is not the same as what we usually use, itssendBroadcast()And the way to do that is byhandlerSend aMessageThe implementation;
3. Now that it’s inside is throughHandlerTo achieve broadcast transmission, then compared to the system broadcast throughBinderAchieving that is certainly more efficient while usingHandlerOther applications cannot send this broadcast to our application, and the broadcast sent within our application will not leave our application;

1.9.3 BroadcastReceiver Security Issues

• BroadcastReceiverIt was designed from a global perspective to facilitate communication between applications and systems, between applications, and within applications, so for a single applicationBroadcastReceiverThere are security issues (malicious scripts constantly sending the broadcasts you receive). To solve this problemLocalBroadcastManagerAnd that’s what happened.
• LocalBroadcastManager 是 Android SupportPackages provide a tool for sending between different components within the same applicationBroadcast.LocalBroadcastManagerAlso known as local notification manager, the benefits of this kind of notification is high security, high efficiency, suitable for local communication, can be used insteadHandlerupdateUI

1.9.4 Broadcast security

• AndroidBroadcasts in the system can communicate directly across processes, which may cause the following two problems:

1. otherAPPCan receive the currentAPPBroadcast sent, resulting in data leakage.
2. otherAPPYou can call the currentAPPBroadcast a message that led toAPPIllegally controlled.

• Send broadcast

1. When sending a broadcast, add the correspondingpermissionIs used for permission verification.
2. inThe Android 4.0Can be used when sending broadcast in the above systemsetPackage()Method to set the name of the packet to receive the broadcast.
3. Use local broadcast.

• Accept radio

1. When registering a broadcast receiver, add the correspondingpermissionIs used for permission verification.
2. Set when registering a broadcast receiverandroid:exportedIs false.

• Use local broadcast

1. When sending a broadcast, if addedpermission
2. The one on the radioAPPYou must apply for permission to receive the broadcast, and vice versa.

1.9.5 Benefits of Using BroadcastReceiver

1. As broadcast data spreads within the application, you don’t have to worry about privacy data leakage.
2. There is no need to worry about other applications forgery broadcast, causing security risks.
3. It is more efficient than sending a global broadcast within the system.

1.10 How to let my broadcast only be received by the specified app?

• Sending a broadcastappEnd, custom defined permissions, then want to receive in additionappThe end must declare permissions to receive.

1. Permission: The protection level is normal.
2. User permissions

<permission android:name="broad.ok.receiver" android:protectionLevel="normal"/>
<uses-permission android:name="broad.ok.receiver" />
Copy the code

3. Send a broadcast with a permission string

public void click(View view) { Intent intent = new Intent(); Intent. PutExtra ("info", "message content "); intent.setAction("myBroadcast.action.call"); sendBroadcast(intent, "broad.ok.receiver"); //sendOrderedBroadcast(intent,"broad.ok.receiver"); }Copy the code

4. Other app recipients who want to access broadcasts must declare permissions in the manifest file

<uses-permission android:name="broad.ok.receiver"/>
Copy the code

1.11 Does broadcast Priority Take effect for Out-of-order Broadcasts?

• Priority also applies to disorder.

1.12 Who has the highest Priority for dynamically registered broadcasts?

• Whoever registers first will be taller

1.13 How do I determine whether the Current BrodcastReceiver receives orderly or out-of-order broadcasts?

• inonReceiverMethod, which calls the return value of the judgment method directly

Public void onReceive(Context Context, Intent Intent) {log. d("MyBroadCastReceiver", "emsp; + intent.getStringExtra("info") + ""); boolean isOrderBroadcast = isOrderedBroadcast(); }Copy the code

1.14 BroadcastReceiver Cannot Perform time-consuming operations

• On the one hand,

1. BroadcastReceiverUsually in the main thread.
2. Time-consuming operations causeANR

• On the other hand

3. BroadcastReceiverThe startup time is short.
4. If only one exists in a processBroadcastReceiverComponents. It also opens child threads to perform time-consuming tasks.
5. The system considers this process to be an empty process with the lowest priority. It’s easy to kill.

conclusion

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1. This article provides a thorough summary of BroadcastReceiver and ContentProvider knowledge. If you have any additional knowledge, please feel free to point it out in the comments section.

2. I hope you found this reading interesting.

Code word is not easy, your praise is my summary of the biggest power!