IllegalStateException (Already attached) when open

Question

I'm trying to develop an app that reads an NFC tag and displays the read data. I took most of the code from a blog but I'm getting an error when I run the application since I am trying to integrate it with the slider application.

Here are my errors and my code below:

E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.example.jeffk11.tag, PID: 20123
                  java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.jeffk11.tag/com.example.jeffk11.tag.MainActivity}: java.lang.IllegalStateException: Already attached
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
                      at android.app.ActivityThread.-wrap12(ActivityThread.java)
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
                      at android.os.Handler.dispatchMessage(Handler.java:102)
                      at android.os.Looper.loop(Looper.java:154)
                      at android.app.ActivityThread.main(ActivityThread.java:6119)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
                   Caused by: java.lang.IllegalStateException: Already attached
                      at android.support.v4.app.FragmentManagerImpl.attachController(FragmentManager.java:2137)
                      at android.support.v4.app.FragmentController.attachHost(FragmentController.java:104)
                      at android.support.v4.app.FragmentActivity.onCreate(FragmentActivity.java:317)
                      at android.support.v7.app.AppCompatActivity.onCreate(AppCompatActivity.java:88)
                      at com.example.jeffk11.tag.MainActivity.onCreate(MainActivity.java:68)
                      at android.app.Activity.performCreate(Activity.java:6679)
                      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726) 
                      at android.app.ActivityThread.-wrap12(ActivityThread.java) 
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477) 
                      at android.os.Handler.dispatchMessage(Handler.java:102) 
                      at android.os.Looper.loop(Looper.java:154) 
                      at android.app.ActivityThread.main(ActivityThread.java:6119) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) 

Code:

package com.example.jeffk11.tag;

import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.view.View;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.nfc.NfcAdapter;
import android.widget.TextView;
import android.widget.Toast;
import android.content.Intent;
import java.io.UnsupportedEncodingException;
import java.util.Arrays;
import android.app.Activity;
import android.app.PendingIntent;
import android.content.IntentFilter;
import android.content.IntentFilter.MalformedMimeTypeException;
import android.nfc.Tag;
import android.nfc.tech.Ndef;
import android.util.Log;
import android.nfc.NdefRecord;
import android.os.AsyncTask;
import android.nfc.NdefMessage;


public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {


    private TextView mTextView;
    private NfcAdapter mNfcAdapter;
    public static final String MIME_TEXT_PLAIN = "text/plain";
    public static final String TAG = "NfcDemo";


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.setDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mTextView = (TextView) findViewById(R.id.textView_explanation);

        mNfcAdapter = NfcAdapter.getDefaultAdapter(this);

        if (mNfcAdapter == null) {
            // Stop here, we definitely need NFC
            Toast.makeText(this, "This device doesn't support NFC.", Toast.LENGTH_LONG).show();
            finish();
            return;

        }

        if (!mNfcAdapter.isEnabled()) {
            mTextView.setText("NFC is disabled.");
        } else {
            mTextView.setText(R.string.explanation);
        }

        handleIntent(getIntent());
    }

    private void handleIntent(Intent intent) {
        String action = intent.getAction();
        if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(action)) {

            String type = intent.getType();
            if (MIME_TEXT_PLAIN.equals(type)) {

                Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
                new NdefReaderTask().execute(tag);

            } else {
                Log.d(TAG, "Wrong mime type: " + type);
            }
        } else if (NfcAdapter.ACTION_TECH_DISCOVERED.equals(action)) {

            // In case we would still use the Tech Discovered Intent
            Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
            String[] techList = tag.getTechList();
            String searchedTech = Ndef.class.getName();

            for (String tech : techList) {
                if (searchedTech.equals(tech)) {
                    new NdefReaderTask().execute(tag);
                    break;
                }
            }

        }
    }

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();

        if (id == R.id.nav_camera) {
            // Handle the camera action
        } else if (id == R.id.nav_gallery) {

        } else if (id == R.id.nav_slideshow) {

        } else if (id == R.id.nav_manage) {

        } else if (id == R.id.nav_share) {

        } else if (id == R.id.nav_send) {

        }

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }

    @Override
    protected void onResume() {
        super.onResume();

        /**
         * It's important, that the activity is in the foreground (resumed). Otherwise
         * an IllegalStateException is thrown.
         */
        setupForegroundDispatch(this, mNfcAdapter);
    }

    @Override
    protected void onPause() {
        /**
         * Call this before onPause, otherwise an IllegalArgumentException is thrown as well.
         */
        stopForegroundDispatch(this, mNfcAdapter);

        super.onPause();
    }

    @Override
    protected void onNewIntent(Intent intent) {
        /**
         * This method gets called, when a new Intent gets associated with the current activity instance.
         * Instead of creating a new activity, onNewIntent will be called. For more information have a look
         * at the documentation.
         *
         * In our case this method gets called, when the user attaches a Tag to the device.
         */
        handleIntent(intent);
    }

    /**
     * @param activity The corresponding {@link Activity} requesting the foreground dispatch.
     * @param adapter  The {@link NfcAdapter} used for the foreground dispatch.
     */
    public static void setupForegroundDispatch(final AppCompatActivity activity, NfcAdapter adapter) {
        final Intent intent = new Intent(activity.getApplicationContext(), activity.getClass());
        intent.setFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);

        final PendingIntent pendingIntent = PendingIntent.getActivity(activity.getApplicationContext(), 0, intent, 0);

        IntentFilter[] filters = new IntentFilter[1];
        String[][] techList = new String[][]{};

        // Notice that this is the same filter as in our manifest.
        filters[0] = new IntentFilter();
        filters[0].addAction(NfcAdapter.ACTION_NDEF_DISCOVERED);
        filters[0].addCategory(Intent.CATEGORY_DEFAULT);
        try {
            filters[0].addDataType(MIME_TEXT_PLAIN);
        } catch (MalformedMimeTypeException e) {
            throw new RuntimeException("Check your mime type.");
        }

        adapter.enableForegroundDispatch(activity, pendingIntent, filters, techList);
    }

    /**
     * @param activity The corresponding {@link BaseActivity} requesting to stop the foreground dispatch.
     * @param adapter  The {@link NfcAdapter} used for the foreground dispatch.
     */
    public static void stopForegroundDispatch(final AppCompatActivity activity, NfcAdapter adapter) {
        adapter.disableForegroundDispatch(activity);
    }


    class NdefReaderTask extends AsyncTask<Tag, Void, String> {

        @Override
        protected String doInBackground(Tag... params) {
            Tag tag = params[0];

            Ndef ndef = Ndef.get(tag);
            if (ndef == null) {
                // NDEF is not supported by this Tag.
                return null;
            }

            NdefMessage ndefMessage = ndef.getCachedNdefMessage();

            NdefRecord[] records = ndefMessage.getRecords();
            for (NdefRecord ndefRecord : records) {
                if (ndefRecord.getTnf() == NdefRecord.TNF_WELL_KNOWN && Arrays.equals(ndefRecord.getType(), NdefRecord.RTD_TEXT)) {
                    try {
                        return readText(ndefRecord);
                    } catch (UnsupportedEncodingException e) {
                        Log.e(TAG, "Unsupported Encoding", e);
                    }
                }
            }

            return null;
        }

        private String readText(NdefRecord record) throws UnsupportedEncodingException {
        /*
         * See NFC forum specification for "Text Record Type Definition" at 3.2.1
         *
         * http://www.nfc-forum.org/specs/
         *
         * bit_7 defines encoding
         * bit_6 reserved for future use, must be 0
         * bit_5..0 length of IANA language code
         */

            byte[] payload = record.getPayload();

            // Get the Text Encoding
            String textEncoding = ((payload[0] & 128) == 0) ? "UTF-8" : "UTF-16";

            // Get the Language Code
            int languageCodeLength = payload[0] & 0063;

            // String languageCode = new String(payload, 1, languageCodeLength, "US-ASCII");
            // e.g. "en"

            // Get the Text
            return new String(payload, languageCodeLength + 1, payload.length - languageCodeLength - 1, textEncoding);
        }

        @Override
        protected void onPostExecute(String result) {
            if (result != null) {
                mTextView.setText("Read content: " + result);
            }
        }
    }
}

Answer 1

You call the onCreate method of the super-class (AppCompatActivity) multiple times in your own onCreate method. Don't do that. super.onCreate() must be called only once (typically this is done at the beginning of your activity's onCreate method. So simply remove the second occurence of

super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);