在 onCreate() 中的 bindService() 之后不调用 onBind() 和 onServiceConnected()答案

【问题标题】：onBind() and onServiceConnected() are not called after bindService() in onCreate()在 onCreate() 中的 bindService() 之后不调用 onBind() 和 onServiceConnected()
【发布时间】：2020-10-05 00:24:42
【问题描述】：

我按照 Google 开发人员文档网站上的教程进行了操作，但可能遗漏了一些内容。我能够正确启动和停止服务，但是现在我尝试绑定到服务，我收到 NullPointerException，因为在 bindService() 之后没有调用 onBind() 和 onServiceConnected()。我在 StackOverflow 上阅读了 10 多个问题，但没有一个有帮助。

我的清单的一部分：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.waveplayer">
    <application
        <service android:name="com.example.waveplayer.ServiceMain"
            android:exported="false"
            android:description="@string/service_description"
            android:enabled="true"/>
    </application>
    <uses-permission android:name="android.permission.FOREGROUND_SERVICE"/>
</manifest>

用于在 OnCreate() 上启动服务的代码：

 Intent intent = new Intent(getApplicationContext(), ServiceMain.class);
            startService(intent);
        getApplicationContext().bindService(intent, connection, BIND_AUTO_CREATE);

 private ServiceConnection connection = new ServiceConnection() {

        @Override
        public void onServiceConnected(ComponentName className, IBinder service) {
            ServiceMain.ServiceMainBinder binder = (ServiceMain.ServiceMainBinder) service;
            serviceMain = binder.getService();
            serviceMainBound = true;
        }

        @Override
        public void onServiceDisconnected(ComponentName arg0) {
            serviceMainBound = false;
        }
    };

还有我的服务代码：

    private Looper serviceMainLooper;

    private ServiceMainHandler serviceMainHandler;

    private final IBinder serviceMainBinder = new ServiceMainBinder();

    private final class ServiceMainHandler extends Handler {

        public ServiceMainHandler(Looper looper) {
            super(looper);
        }

        @Override
        public void handleMessage(Message msg) {

        }
    }

    @Override
    public void onCreate() {
        super.onCreate();
        HandlerThread thread = new HandlerThread("ServiceMainStartArguments",
                Process.THREAD_PRIORITY_BACKGROUND);
        thread.start();
        serviceMainLooper = thread.getLooper();
        serviceMainHandler = new ServiceMainHandler(serviceMainLooper);
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Toast.makeText(this, "service starting", Toast.LENGTH_SHORT).show();
        // For each start request, send a message to start a job and deliver the
        // start ID so we know which request we're stopping when we finish the job
        Message msg = serviceMainHandler.obtainMessage();
        msg.arg1 = startId;
        serviceMainHandler.sendMessage(msg);

        Intent notificationIntent = new Intent(this, ServiceMain.class);
        PendingIntent pendingIntent =
                PendingIntent.getActivity(this, 0, notificationIntent, 0);
        String CHANNEL_ID = "ServiceMain";
        RemoteViews notificationLayout = new RemoteViews(getPackageName(), R.layout.notification_song_pane);
        NotificationCompat.Builder builder = new NotificationCompat.Builder(this, CHANNEL_ID)
                .setPriority(NotificationCompat.PRIORITY_MAX)
                .setVisibility(NotificationCompat.VISIBILITY_PUBLIC)
                .setStyle(new NotificationCompat.DecoratedCustomViewStyle())
                .setCustomContentView(notificationLayout)
                .setContentIntent(pendingIntent);
        startForeground(CHANNEL_ID.hashCode(), builder.build());
        return START_STICKY;
    }

    public class ServiceMainBinder extends Binder {
        ServiceMain getService() {
            return ServiceMain.this;
        }
    }

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



    @Override
    public void onDestroy() {
        saveFile();
        Toast.makeText(this, "service done", Toast.LENGTH_SHORT).show();
    }

【问题讨论】：

服务是否真正启动并调用它的onBind？
没有。该服务甚至还没有开始。我之前就开始了。
好的，所以服务直到 onStart() 之后才会启动。我应该在哪里绑定到服务？

标签： android service

【解决方案1】：

事实证明，直到 UI 线程清除 Activity 中的代码后，才创建服务，因此直到我的 Activity 的 onStart() 方法之后我才能访问它。这就是onServiceConnected() 回调方法的用途。至此，Service 已创建，Activity 可以访问 Service。

【讨论】：