读取 NFC 标签，直到它被分离并在读取标签时更新 UI

Question

我想读取 NFC 标签，直到设备远离 NFC 标签。然后我想做一些活动。我已经设法使用while循环来读取标签并捕获InterruptedException。而且我还想在读取 while 循环内的标签时更新 UI。当我在 while 循环中时，我找不到更新 UI 的方法。

更新 UI 的数据来自 onLocationChanged-listener。

public void onLocationChanged(Location location) {
    if (location.hasSpeed()) {
        /*double speed=location.getSpeed() * 3.6;;
        while (1==1)
        {*/
        speed = location.getSpeed() * 3.6;
        String units="km/h";
        s= new SpannableString(String.format(Locale.ENGLISH, "%.0f %s", speed, units));
        s.setSpan(new RelativeSizeSpan(0.45f), s.length()-units.length()-1, s.length(), 0);
        updateUI();

    }
}

public void updateUI(){
    drivingMode=findViewById(R.id.txtDriving);
    currentSpeed = findViewById(R.id.valSpeed);
      if (currentSpeed!=null) {
        currentSpeed.setText(s);
        if (speed > 10) {
            drivingMode.setText(R.string.msg_driving);
            isDriving = true;
        } else {
            drivingMode.setText(R.string.msg_notDriving);
            isDriving=false;
        }
    }
}

private void readFromNFC( Ndef ndef)  {
            try
            {
                ndef.connect();
                NdefMessage ndefMessage = ndef.getNdefMessage();
                ndef.close();
                String message = new String(ndefMessage.getRecords()[0].getPayload());
                // Log.d(TAG, "readFromNFC Before Pass: " + message);
                //Toast.makeText(this, "Text" + message, Toast.LENGTH_LONG).show();
                if (message.equals("in")) {
                    Toast.makeText(this.getApplicationContext(), R.string.message_nfc_holder_detected, Toast.LENGTH_LONG).show();
                    if (isDialogshowing) {
                        dialog.dismiss();
                        isEmergency=false;
                    }
                    while (1 == 1) {
                        ndef.connect();
                        ndefMessage = ndef.getNdefMessage();
                        message = new String(ndefMessage.getRecords()[0].getPayload());
                        //Log.d(TAG, "readFromNFCPassed: " + message);
                        TimeUnit.SECONDS.sleep(1);
                        ndef.close();
                        updateUI();
                    }

                } else {
                    Toast.makeText(this.getApplicationContext(), R.string.message_nfc_holder_error, Toast.LENGTH_LONG).show();
                    ndef.close();
                }

            } catch (IOException | FormatException | InterruptedException e ) {
                e.printStackTrace();
                Toast.makeText(this.getApplicationContext(), R.string.message_nfc_holder_detached, Toast.LENGTH_LONG).show();
                if(isDriving) {
                    activateEmergency();
                }
                else
                {
                    if (isDialogshowing) {
                        dialog.dismiss();
                        dialog.dismiss();
                        isDialogshowing = false;
                    }

                }
            }
}

Answer 1

为了在不阻塞主 UI 线程的情况下持续读取 UI 线程，您可以使用 AsyncTask。这还允许您使用 onProgressUpdate() 回调将状态更新发布到 UI（线程）。

你的 AsyncTask 可能看起来像这样：

private class ProcessNFCTask extends AsyncTask<Ndef, NdefMessage, Void> {
    protected Void doInBackground(Ndef... tag) {
        // This happens on the worker thread!

        // TODO: content of readFromNFC(Ndef ndef);
        // Instead of calling updateUI(), you would call publishProgress(message).
        // You can use whatever represents your progress instead of "message".
        // Instead of doing your finalization stuff (what you currently have
        // in the catch clause) here, you would want to do that in
        // onPostExecute() instead.
    }

    protected void onProgressUpdate(NdefMessage... progress) {
        // This happens on the UI thread!

        // You may also use the progress status information provided in
        // "progress" here. This is what you pass to publishProgress(...).
        updateUI();
    }

    protected void onPostExecute(Void result) {
        // This happens on the UI thread!

        // TODO: Whatever you want to do when you are finished reading, e.g.:
        if (isDriving) {
            activateEmergency();
        } else {
            if (isDialogshowing) {
                dialog.dismiss();
                dialog.dismiss();
                isDialogshowing = false;
            }
        }
    }

}