为什么这种显式广播不起作用？

Question

我正在尝试向在活动中动态注册的接收器发送显式广播，但它似乎不起作用。我尝试添加意图过滤器期望的操作，但这也不起作用。只有当我使用公共隐含意图时，它才会接收广播。

谁能告诉我为什么？该代码适用于 Android 8.0+，我在 CustomReceiver 中标记了该行。

总之应该...

1. 服务启动，动态注册一个 CustomReceiver 来监听隐式广播。
2. CustomReceiver 接收到隐式广播，尝试向 MainActivity 发送显式广播。
3. MainActivity 接收器捕获显式广播并执行某些操作。

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.demos.democode">

    <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />

    <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">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <service
            android:name=".CustomService" />
    </application>

</manifest>

MainActivity.java

package com.demos.democode;

import androidx.appcompat.app.AppCompatActivity;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.util.Log;

public class MainActivity extends AppCompatActivity {

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

        IntentFilter intentFilter = new IntentFilter(CustomService.customActionActivity);
        getApplicationContext().registerReceiver(activityReceiver, intentFilter);

        Intent serviceIntent = new Intent(this,CustomService.class);
        this.startForegroundService(serviceIntent);

        Log.d("DEMO_APP", "create");

    }

    BroadcastReceiver activityReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {

            Log.d("DEMO_APP", "activity receiver");

        }
    };

}

CustomReceiver.java - 此处的显式广播不起作用。

package com.demos.democode;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.util.Log;

public class CustomReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {

        Log.d("DEMO_APP", "custom receiver");

        // DOESN'T WORK! this explicit broadcast doesn't work even after setting an action in - why?
        Intent i = new Intent(context, MainActivity.class);
        i.setAction(CustomService.customActionActivity);
        context.sendBroadcast(i);

        // this implicit public broadcast works fine
        i = new Intent(CustomService.customActionActivity);
        context.sendBroadcast(i);

    }

}

CustomService.java

package com.demos.democode;

import android.app.Notification;
import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.app.Service;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.IBinder;
import android.util.Log;

import androidx.annotation.Nullable;
import androidx.core.app.NotificationCompat;
import androidx.core.app.NotificationManagerCompat;

public class CustomService extends Service {

    protected Context context = null;
    public static String customAction = "EVENT_1";
    public static String customActionActivity = "EVENT_2";

    @Override
    public void onCreate() {
        super.onCreate();

        context = getApplicationContext();

        NotificationChannel serviceChannel = new NotificationChannel(
                "DEMO_CHANNEL",
                "Demo App",
                NotificationManager.IMPORTANCE_LOW
        );
        NotificationManager manager = getSystemService(NotificationManager.class);
        manager.createNotificationChannel(serviceChannel);

        Notification notification = new NotificationCompat.Builder(context, "DEMO_CHANNEL")
                .setSmallIcon(R.drawable.ic_launcher_foreground)
                //.setContentText("Total screen time today: " + totalTimeDisplay )
                .build();
        NotificationManagerCompat notificationManager = NotificationManagerCompat.from(context);
        notificationManager.notify(1, notification);
        startForeground(1, notification);

        IntentFilter intentFilter = new IntentFilter(customAction);

        CustomReceiver customReceiver = new CustomReceiver();
        context.registerReceiver( customReceiver , intentFilter);

        Log.d("DEMO_APP", "service created");

    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {

        final Intent i = new Intent(customAction);

        Log.d("DEMO_APP", "service started");
        sendBroadcast(i);

        return Service.START_NOT_STICKY;
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
    }

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }
}

Answer 1

您正在尝试使用sendBroadcast() 启动Activity

在这段代码中：

    // DOESN'T WORK! this explicit broadcast doesn't work even after setting an action in - why?
    Intent i = new Intent(context, MainActivity.class);
    i.setAction(CustomService.customActionActivity);
    context.sendBroadcast(i);

您正在尝试启动Activity，因此最后一行需要：

    content.startActivity(i);

Answer 2

对不起，我迟到了，但我认为错误是在MainActivity 中注册接收者。你用过

getApplicationContext().registerReceiver(activityReceiver, intentFilter);

它使用应用程序上下文来注册接收器。 它应该被替换为：

registerReceiver(activityReceiver, intentFilter);

接收者将在其中注册 Context 的特定活动实例。