BroadcastReceiver goAsync() 返回 null PendingResult

Question

我有一个BroadcastReceiver我想在 UI 线程之外执行一些工作。根据文档中的示例BroadcastReceiver，我首先调用goAsync()，它返回一个PendingResult，然后在我的非 UI 线程中调用PendingResult.finish().

但是，我得到了NullPointerException因为goAsync()返回null。

我究竟做错了什么？

这是一个复制行为的简单示例。我用过targetSdkVersion 27和minSdkVersion 23：

package com.example.broadcastreceiverpendingintenttest;

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

public class MyReceiver extends BroadcastReceiver {

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

        PendingResult pendingResult = goAsync();

        AsyncTask<Void, Void, Void> asyncTask = new AsyncTask<Void, Void, Void>() {

            @Override
            protected Void doInBackground(Void... voids) {
                Log.i("tag", "performed async task");
                pendingResult.finish();
                return null;
            }
        };

        asyncTask.execute();
    }
}

这是一个简单的 Activity 调用它：

package com.example.broadcastreceiverpendingintenttest;

import android.content.Intent;
import android.content.IntentFilter;
import android.support.v4.content.LocalBroadcastManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    public static final String ACTION = "MY_ACTION";

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

        LocalBroadcastManager broadcastManager = LocalBroadcastManager.getInstance(this);
        IntentFilter intentFilter = new IntentFilter(ACTION);
        broadcastManager.registerReceiver(new MyReceiver(), intentFilter);

        Button button = findViewById(R.id.button);
        button.setOnClickListener(v -> {
            broadcastManager.sendBroadcast(new Intent(ACTION));
        });
    }
}

activity_main.xml：

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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="com.example.broadcastreceiverpendingintenttest.MainActivity">

    <Button
        android:id="@+id/button"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginBottom="232dp"
        android:layout_marginEnd="148dp"
        android:layout_marginStart="148dp"
        android:layout_marginTop="231dp"
        android:text="Press me"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

Answer 1

我写了一个JobIntentService：

package com.example.broadcastreceiverpendingintenttest;

import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.v4.app.JobIntentService;
import android.util.Log;

public class MyJobIntentService extends JobIntentService {

    public static final String ACTION = "and....action!";

    static final int JOB_ID = 9001;

    @Override
    protected void onHandleWork(@NonNull Intent intent) {
        // TODO check the intent action is valid, get extras etc
        Log.i("tag", "performed my task");
    }
}

其声明AndroidManifest如下：

<service
    android:name=".MyJobIntentService"
    android:permission="android.permission.BIND_JOB_SERVICE"
    android:exported="false" />

MyReceiver然后将服务的工作排队：

package com.example.broadcastreceiverpendingintenttest;

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

public class MyReceiver extends BroadcastReceiver {

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

        Intent jobIntent = new Intent();
        jobIntent.setAction(MyJobIntentService.ACTION);
        MyJobIntentService.enqueueWork(context, MyJobIntentService.class, MyJobIntentService.JOB_ID, jobIntent);
    }
}

开销比我想要的要多一些，但它完成了工作。