Android learning six – broadcast mechanism
Introduction to Broadcasting Mechanism
Android applications can register broadcasts they are interested in, so that they can receive the broadcast content they care about, either from the system or from the application. Android provides a complete set of apis that allow applications to receive and send broadcasts. BroadcasReceiver is needed to receive broadcasts
First of all, broadcasting is divided into standard broadcasting and orderly broadcasting
Standard broadcast: a broadcast executed completely asynchronously. After a broadcast is sent, all BroadCasReceivers receive the broadcast message almost simultaneously, all efficient, but not truncated.
Orderly broadcast: It feels like a queue. Only one BroadcasReceiver receives a broadcast message at a time, but after the logic of this BroadcasReceiver is executed, the next BroadcasReceiver receives it and passes it out in turn. BroadcasReceiver with a higher priority receives the message first and then sequentially. The ordered broadcast can be truncated. Once truncated, the message cannot be received.
Dynamic registration listens for time changes
Dynamic registration is registered in code. First we build a BroadcastTest project, define an inner class in ManActivity that extends BroadcasReceiver, and override the parent onReceive method so that it will be executed over time
package com.example.broadcastreceiver
import android.content.BroadcastReceiver
import android.content.Context
import android.content.Intent
import android.content.IntentFilter
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Toast
class MainActivity : AppCompatActivity() {
lateinit var timeChangerReceiver:TimeChangeRecevier
override fun onCreate(savedInstanceState: Bundle?). {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
// Get IntentFilter instance
val intentFilter=IntentFilter()
/ / but time changes, the system will issue a value of "android. Intent. Action. TIME_TICK" broadcast
// What broadcasts does the BroadcastReceiver want to listen on
intentFilter.addAction("android.intent.action.TIME_TICK")
timeChangerReceiver=TimeChangeRecevier()
/ / this method is to register, such ability can accept value for android. The intent. The action. The TIME_TICK broadcasting
registerReceiver(timeChangerReceiver,intentFilter)
}
override fun onDestroy(a) {
super.onDestroy()
// Cancel registration here, otherwise it will cause memory overflow
unregisterReceiver(timeChangerReceiver)
}
inner class TimeChangeRecevier:BroadcastReceiver() {override fun onReceive(context: Context? , intent:Intent?). {
Toast.makeText(context,"This has changed",Toast.LENGTH_SHORT).show()
}
}
}
Copy the codeThe effect of broadcasting over time is as follows
Static registration to achieve boot
Dynamic registration is flexible, but can only be accepted after the application is started, whereas static registration is used.
Dynamically register to listen to the radio in theory, then the static should also can, in the past can indeed, but because there are a large number of malicious programs using this mechanism when to start the program broadcasting system monitoring, resulted in the background of mobile phone frequent awakening, seriously affect the performance of mobile phones and battery, so every time the android version update, almost will weaken the function of static registration, Static registration is no longer allowed for all hermit broadcasts since Android8.0.
Hermit broadcast: A broadcast to which application is not specifically specified
Of course, some special broadcasts are allowed: boot broadcasts, for example
android.intent.action.BOOT_COMPLETED
Copy the codeDynamically registering us through internal classes, now we’ll create it through the Android Studio shortcut, Right-click on the com. Example. Broadcastreceiver – > new – > other – > I changed the name of the class to BootCompleteReceiver Broadcast Receiver here
Exprodted: allows this BroadcasReceive to accept broadcasts outside the program
Enabled: Indicates whether to enable BroadcasReceive
Now modify the code of the BootCompleteReceiver class to pop up the prompt message using Toast in the onReceived method
package com.example.broadcastreceiver
import android.content.BroadcastReceiver
import android.content.Context
import android.content.Intent
import android.widget.Toast
class BootCompleteReceiver : BroadcastReceiver() {
override fun onReceive(context: Context, intent: Intent) {
// This method is called when the BroadcastReceiver is receiving an Intent broadcast.
Toast.makeText(context,"Boot Complete",Toast.LENGTH_SHORT).show()
}
}
Copy the codeStatically registered BroadcasReceiv must be registered in activitymanifest.xml. Since we registered it using a shortcut, we registered it directly, as shown in the following example:
<receiver
android:name=".BootCompleteReceiver"
android:enabled="true"
android:exported="true"></receiver>
Copy the codeTo receive a startup broadcast, you have to modify the Activitymanifest.xml code to add because of permissions
<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"/>
Copy the codeFinally, add the action under the <receiver TAB
<receiver
android:name=".BootCompleteReceiver"
android:enabled="true"
android:exported="true">
<intent-filter>
<action android:name="android.intent.action.BOOT_COMPLETED"/>
</intent-filter>
Copy the codeA BroadcastReceiver is defined to receive broadcasts
package com.example.broadcastreceiver
import android.content.BroadcastReceiver
import android.content.Context
import android.content.Intent
import android.widget.Toast
class MyBoardcastReceiver : BroadcastReceiver() {
override fun onReceive(context: Context, intent: Intent) {
// This method is called when the BroadcastReceiver is receiving an Intent broadcast.
Toast.makeText(context,"recevied in MYboardcastReciver",Toast.LENGTH_SHORT).show()
}
}
Copy the codeThen in ActivityManifest modify BroadcastReceiver and making BoardcastReceiver accept com here. Example. Broadcasttest. MY_BRPADCAST broadcasting
<receiver
android:name=".MyBoardcastReceiver"
android:enabled="true"
android:exported="true">
<intent-filter>
<action android:name="com.example.broadcasttest.MY_BRPADCAST"/>
</intent-filter>
</receiver>
Copy the codeTo send this broadcast, modify the man.xml code to add a button layout
<? The XML version = "1.0" encoding = "utf-8"? > <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical"> <Button android:id="@+id/button" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="Send Broadcast"/> </LinearLayout>Copy the codeThen set up the listener in ManActivity
Start by building an Intent object that passes in a send broadcast
Call intent.setpackage (packageName) to pass in the packageName of the current application
SendBroadcast (Intent) Specifies that the broadcast is sent to a specific application
class MainActivity : AppCompatActivity() { lateinit var timeChangerReceiver:TimeChangeRecevier override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) val button:Button=findViewById(R.id.button) button.setOnClickListener{ val intent=Intent("comcom.example.broadcasttest.MY_BRPADCAST") intent.setPackage(packageName) sendBroadcast(intent) } .....Copy the codeOrderly broadcast
Create a BoradcastReceiver in shortcut to accept the same broadcast
package com.example.myapplication
import android.content.BroadcastReceiver
import android.content.Context
import android.content.Intent
import android.widget.Toast
class MyReceiver2 : BroadcastReceiver() {
override fun onReceive(context: Context, intent: Intent) {
// The pop-up message that receives the broadcast message becomes up up
Toast.makeText(context,"up up ", Toast.LENGTH_SHORT).show()
}
}
Copy the codeIn androidmanifest.xml, change the priority to 100. This broadcast is the first to receive messages
<intent-filter android:priority="100">
Copy the codeYou can then block the broadcast and not transmit it
class MyReceiver : BroadcastReceiver() {
override fun onReceive(context: Context, intent: Intent) {
// This method is called when the BroadcastReceiver is receiving an Intent broadcast.
Toast.makeText(context,"up up day day",Toast.LENGTH_SHORT).show()
abortBroadcast()// Cut off the broadcast}}Copy the codeBroadcastReceiver best practices
Simulate forced logout after login
1. First we create a class to manage all activities
package com.example.broadcastreceiver
import android.app.Activity
// This class manages the closing and adding of all activities
object Activityall {
private val activityaes=ArrayList<Activity>()
fun addActivty(activity: Activity){
activityaes.add(activity)
}
fun removeactivity(activity: Activity){
activityaes.remove(activity)
}
fun allActivity(a){
for (activity in activityaes){
if(! activity.isFinishing){ activity.finish() } } activityaes.clear() } }Copy the codeWe then create a BaseActivity class to be the parent of all activities, because our forced logout function means that you have to force out no matter what class you are in, so the logic for exiting and accepting registration broadcasts and unregistering is all done in this class
package com.example.broadcastreceiver
import android.content.BroadcastReceiver
import android.content.Context
import android.content.Intent
import android.content.IntentFilter
import android.os.Bundle
import android.os.PersistableBundle
import androidx.appcompat.app.AlertDialog
import androidx.appcompat.app.AppCompatActivity
open class BaseActivity: AppCompatActivity() {
lateinit var recevier:ForReceiver
override fun onCreate(savedInstanceState: Bundle?). {
super.onCreate(savedInstanceState)
Activityall.addActivty(this)}override fun onResume(a) {
super.onResume()
val intentFilter=IntentFilter()
intentFilter.addAction("com.example.FOLL_PO")
recevier=ForReceiver()
registerReceiver(recevier,intentFilter)
}
override fun onPause(a) {
super.onPause()
unregisterReceiver(recevier)
}
override fun onDestroy(a) {
super.onDestroy()
Activityall.removeactivity(this)}inner class ForReceiver:BroadcastReceiver() {
override fun onReceive(context: Context, intent: Intent) {
AlertDialog.Builder(context).apply {
setTitle("Offline")
setMessage("You're out. Get off the line.")
setCancelable(false)// Cannot force exit
setPositiveButton("Ok") { _, _ ->
Activityall.allActivity()
val i = Intent(context, LoginActivity::class.java)
context.startActivity(i)
}
show()
}
}
}
}
Copy the codeNext build a LoginActivity as the login interface
package com.example.broadcastreceiver
import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Button
import android.widget.EditText
import android.widget.Toast
import androidx.core.content.withStyledAttributes
class LoginActivity : BaseActivity() {
override fun onCreate(savedInstanceState: Bundle?). {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_login)
val login:Button=findViewById(R.id.login)
login.setOnClickListener {
val zh:EditText=findViewById(R.id.zh)
val zh2=zh.text.toString();
val mm:EditText=findViewById(R.id.mm)
val mm2=mm.text.toString();
if (zh2=="abc"&&mm2=="123") {val intent=Intent(this,MainActivity::class.java)
startActivity(intent)
}else{
Toast.makeText(this."Wrong password or account number for young man.",Toast.LENGTH_SHORT).show()
}
}
}
}
Copy the code<? xml version="1.0" encoding="utf-8"? > <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
>
<LinearLayout
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="60dp">
<TextView
android:layout_width="90dp"
android:layout_height="wrap_content"
android:layout_gravity="center_vertical"
android:textSize="18sp"
android:text="Account." />
<EditText
android:id="@+id/zh"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:layout_gravity="center_vertical" />
</LinearLayout>
<LinearLayout
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="60dp">
<TextView
android:layout_width="90dp"
android:layout_height="wrap_content"
android:layout_gravity="center_vertical"
android:textSize="18sp"
android:text="Password" />
<EditText
android:id="@+id/mm"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:layout_gravity="center_vertical"
android:inputType="textPassword" />
</LinearLayout>
<Button
android:id="@+id/login"
android:layout_width="200dp"
android:layout_height="60dp"
android:layout_gravity="center_horizontal"
android:text="Login" />
</LinearLayout>
Copy the codeVerify the correctness of the account and password in LoginActivity
package com.example.broadcastreceiver
import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Button
import android.widget.EditText
import android.widget.Toast
import androidx.core.content.withStyledAttributes
class LoginActivity : BaseActivity() {
override fun onCreate(savedInstanceState: Bundle?). {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_login)
val login:Button=findViewById(R.id.login)
login.setOnClickListener {
val zh:EditText=findViewById(R.id.zh)
val zh2=zh.text.toString();
val mm:EditText=findViewById(R.id.mm)
val mm2=mm.text.toString();
if (zh2=="abc"&&mm2=="123") {// The login page is displayed after forcibly logging out
val intent=Intent(this,MainActivity::class.java)
startActivity(intent)
}else{
Toast.makeText(this."Wrong password or account number for young man.",Toast.LENGTH_SHORT).show()
}
}
}
}
Copy the codeAdd a button to the ManActivity that triggers a forced logout
<? xml version="1.0" encoding="utf-8"? > <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
>
<Button
android:id="@+id/tc"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="tuichu"/>
</LinearLayout>
Copy the codeModify the MainActivity code
package com.example.broadcastreceiver
import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Button
class MainActivity : BaseActivity() {
override fun onCreate(savedInstanceState: Bundle?). {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val tuichu:Button=findViewById(R.id.tc)
tuichu.setOnClickListener {
val intent=Intent("com.example.FOLL_PO")
// Send a broadcast
sendBroadcast(intent)
}
}
}
Copy the codeFinally, be sure to change the LoginActivity login screen to the main Activity
<activity android:name=".LoginActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
Copy the codeRun last if the password is wrong
If yes, the page after login is redirected
Click this button to simulate forced logout
Click OK to return to the login screen