SMS接收方侦听器始终为null

Question

自定义侦听器出现问题。我的主要需求是将来自接收器类的传入短信传递给主要活动。不幸的是，它不起作用，我也不明白为什么。

我的MainActivity：

@RequiresApi(api = Build.VERSION_CODES.M)
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        keepFullscreen();

        countdownTimer = findViewById(R.id.countdown_text);
        setContentView(R.layout.activity_main);


        SmsReceiver smsReceiver = new SmsReceiver();
        smsReceiver.setOnSmsReceivedListener(new SmsReceiver.OnSmsReceivedListener() {
            @Override
            public void onSmsReceived(String sender, String message) {
                Toast.makeText(MainActivity.this, message + " von " + sender, Toast.LENGTH_SHORT).show();
                //setIngoingSms(sender, message);
            }
        });

// and so on...

我也已经设置了BroadcastReceiver，但是由于侦听器始终为null，所以它不起作用：

public class SmsReceiver extends BroadcastReceiver {

    // Set variables
    private static final String TAG = SmsReceiver.class.getSimpleName();
    public static final String pdu_type = "pdus";


    public interface OnSmsReceivedListener {
        public void onSmsReceived(String sender, String message);
    }

    private OnSmsReceivedListener listener;

    @RequiresApi(api = Build.VERSION_CODES.M)
    public SmsReceiver() {
        this.listener = null;
    }

    public void setOnSmsReceivedListener(OnSmsReceivedListener listener) {
        this.listener = listener;
    }

    @RequiresApi(api = Build.VERSION_CODES.M)
    @Override
    public void onReceive(Context context, Intent intent){
        String str = "";
        String snd = "";
        if(intent.getAction() != null){
            Bundle bundle = intent.getExtras();
            if (bundle != null) {
                Object[] pdus = (Object[]) bundle.get(pdu_type);
                final SmsMessage[] messages = new SmsMessage[pdus.length];
                for (int i = 0; i < pdus.length; i++) {
                    messages[i] = SmsMessage.createFromPdu((byte[]) pdus[i], bundle.getString("format"));
                    snd = messages[i].getOriginatingAddress();
                    str+= messages[i].getMessageBody();
                    if (listener != null) {
                        listener.onSmsReceived(snd, str);
                    }
                }
            }
        }
    }


}

我真的希望你能帮助我。谢谢！