无法读取Lollipop下方的来电号码

Question

当API低于21时，我的应用程序无法读取传入的号码。如何才能使其正常工作？我试过这种方法：http://mmarvick.github.io/blog/blog/lollipop-multiple-broadcastreceiver-call-state/但不起作用

代码：

public class PhoneStateBroadcastReceiver extends BroadcastReceiver {

private static final String TAG = "PhoneStateBroadcast";
Context mContext;
String incoming_nr;
private static int prev_state;
static CustomPhoneStateListener customPhoneListener;

@Override
public void onReceive(Context context, Intent intent) {
    TelephonyManager telephony = (TelephonyManager)context.getSystemService(Context.TELEPHONY_SERVICE); //TelephonyManager object
    if(customPhoneListener == null){
        customPhoneListener = new CustomPhoneStateListener();
        telephony.listen(customPhoneListener, PhoneStateListener.LISTEN_CALL_STATE);
    }

    Bundle bundle = intent.getExtras();
    String phoneNr = bundle.getString("incoming_number");
    incoming_nr = phoneNr;
    Log.v(TAG, "phoneNr: " + phoneNr);
    mContext = context;
}

public class CustomPhoneStateListener extends PhoneStateListener {

    private static final String TAG = "CustomPhoneStateListnr";

    @Override
    public void onCallStateChanged(int state, String incomingNumber){
        if(incomingNumber != null && incomingNumber.length() > 0){
            incoming_nr = incomingNumber;
        }

        //if(prev_state == state) return;

        switch(state){
            case TelephonyManager.CALL_STATE_RINGING:
                Log.d(TAG, "CALL_STATE_RINGING");
                prev_state = state;
                break;
            case TelephonyManager.CALL_STATE_OFFHOOK:
                Log.d(TAG, "CALL_STATE_OFFHOOK");
                prev_state = state;
                break;
            case TelephonyManager.CALL_STATE_IDLE:
                Log.d(TAG, "CALL_STATE_IDLE==>"+incoming_nr);
                if(prev_state == TelephonyManager.CALL_STATE_OFFHOOK){

                    Intent i = new Intent(mContext, PostCallPromptActivity.class);
                    i.putExtra(Constants.EXTRA_CALL_LOG_NUMBER, incomingNumber);
                    i.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                    mContext.startActivity(i);

                    prev_state = state;
                    //Answered Call which is ended
                }
                if((prev_state == TelephonyManager.CALL_STATE_RINGING)){
                    prev_state = state;
                    //Rejected or Missed call
                }
                break;
        }
    }
}

}