广播接收器在 Android Studio 4.0.0 中不起作用

Question

I am new to Android Studio and the broadcast receiver is not working.

"Broadcast Received.!!" doesn't appear on the screen.

Android Studio version: 4.0

Android Version in the emulator: Android 10 (Q)

SendBroadcast Project:

MainActivity.java:

package com.example.sendbroadcast;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;

public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
}

public void sendBroadcast(View view) {
    Intent intent = new Intent();
    intent.setAction("com.example.sendbroadcast");
    intent.addFlags(Intent.FLAG_INCLUDE_STOPPED_PACKAGES);
    sendBroadcast(intent);
    System.out.println("Sent!!!");
}
  }

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<Button
    android:id="@+id/send_broadcast_button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:onClick="sendBroadcast"
    android:text="Send Broadcast"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

ReceiveBroadcast project:

MyReceiver.java:

package com.example.recievebroadcast;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.widget.Toast;

public class MyReceiver extends BroadcastReceiver {

   @Override
   public void onReceive(Context context, Intent intent) {
       System.out.println("Received!!!");
       Toast.makeText(context, "Broadcast Received!!!", Toast.LENGTH_LONG).show();
   }
 }

AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <receiver
        android:name=".MyReceiver"
        android:enabled="true"
        android:exported="true"
        >
        <intent-filter>
            <action android:name="com.example.sendbroadcast"></action>
        </intent-filter>
    </receiver>
</application>

Answer 1

Implicit broadcasts like this one have been blocked on Android since Android 8.0 , nearly three years ago.

Answer 2

Implicit broadcasts are blocked to prevent unwanted apps from matching your intent and starting (that's why they will only work with receivers registered at runtime).

Since you're sending broadcast to specific receiver you can modify your intent to be explicit by declaring target package:

public void sendBroadcast(View view) {
    Intent intent = new Intent();
    intent.setAction("com.example.sendbroadcast");
    // add this line to have intent delivered explicitly to your app
    // use package name of your ReceiveBroadcast project
    intent.setPackage("com.example.recievebroadcast");
    intent.addFlags(Intent.FLAG_INCLUDE_STOPPED_PACKAGES);
    sendBroadcast(intent);
    System.out.println("Sent!!!");
}