NullPointerException TextView.setText（CharSequence），尚不清楚其如何仍然为null

Question

I've been trying for a little bit now to just get my app launching again. I modified how I pulled bitcoin price data to allow for user preferences. However since doing this I get a NullPointerException from my TextView currentPriceDisplay elements method. currentPriceDisplay.setText(getmBitcoinPrice());

I have modified values throughout my code to prevent this variable from ever actually being null, I've also checked my nav_header_main.xml file to see if I was referencing the right TextView I am. So at this point pretty stumped and I have to go to the day job. If you can have a look at my code and see if you notice anything that would be great.

MainActivity:

package com.instacoind.www.coind;

import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.AsyncTask;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.support.annotation.Nullable;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.util.Log;
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.widget.TextView;

import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.Map;
import java.util.Set;

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {

    private Double mBitcoinPrice = 0.0;
    public Double getmBitcoinPrice(){
        return mBitcoinPrice;
    }
    public void setmBitcoinPrice(Double price){
        this.mBitcoinPrice = price;
    }
    private Double mBitcoinPriceOld = 0.0;
    public Double getmBitcoinPriceOld(){
        return mBitcoinPriceOld;
    }
    public void setmBitcoinPriceOld(Double price){
        this.mBitcoinPriceOld = price;
    }
    @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) {
                if(mBitcoinPrice != 0.0) {
                    Snackbar.make(view, "Last Change: " + priceChange(), Snackbar.LENGTH_LONG)
                            .setAction("Action", null).show();
                }else{
                    Snackbar.make(view, "SYNC FAILED ERROR::01", 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);
    }

    @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) {
            Intent start_settings = new Intent(this, SettingsActivity.class);
            startActivity(start_settings);
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    protected void onStart(){
        super.onStart();
        updatePrice();
    }

    @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) {

        }

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

    public void updatePrice(){
        GetBitcoinPrice worker = new GetBitcoinPrice();
        worker.execute(getPrefFiat(this), getPrefPriceIndex(this));
        refreshPriceDisplays();
    }
    public static String getPrefFiat(Context context){
        SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);
        return prefs.getString(context.getString(R.string.pref_currency_key),
                context.getString(R.string.pref_currency_def));
    }
    public static String getPrefPriceIndex(Context context){
        SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);
        return prefs.getString(context.getString(R.string.pref_source_key),
                context.getString(R.string.pref_source_default));
    }
    public String priceChange(){
        Double past = getmBitcoinPriceOld();
        Double pres = getmBitcoinPrice();
        Double change = 0.0;
        String fin = "price_change";
        if(past != null){
            if(pres >= past){
                change = pres - past;
                fin = "+ " + Double.toString(change);
            }else if(pres <= past){
                change = past - pres;
                fin = "- " + Double.toString(change);
            }
        }else{
            setmBitcoinPriceOld(getmBitcoinPrice());
        }
        return fin;
    }
    public void refreshPriceDisplays(){
        TextView PriceDisplay = (TextView) findViewById(R.id.current_price_display);
        String error = "No Bitcoin Price";
        try {
            Log.v("RefreshPriceDisplays", "mBitcoinPrice: " + Double.toString(getmBitcoinPrice()));
            PriceDisplay.setText(Double.toString(getmBitcoinPrice()));
        }catch(NullPointerException e) {
            Log.v("RefreshPriceDisplays", "mBitcoinPrice NULL");
            PriceDisplay.setText("ERR");
        }
    }


    private class GetBitcoinPrice extends AsyncTask<String, Void, Double> {

        public String mPrefFiat;
        public String mPrefIndex;

        protected Double doInBackground(String... params) {

            // These two need to be declared outside the try/catch
            // so that they can be closed in the finally block.
            HttpURLConnection urlConnection = null;
            BufferedReader reader = null;

            // Will contain the raw JSON response as a string.
            String bitcoinJsonStr = null;
            this.mPrefFiat = params[0];
            this.mPrefIndex = params[1];



            try {
                // Construct the URL for the OpenWeatherMap query
                // Possible parameters are avaiable at OWM's forecast API page, at
                // http://openweathermap.org/API#forecast
                URL url = new URL(buildUrl(this.mPrefFiat,this.mPrefIndex));

                // Create the request to Index Source, and open the connection
                urlConnection = (HttpURLConnection) url.openConnection();
                urlConnection.setRequestMethod("GET");
                urlConnection.connect();

                // Read the input stream into a String
                InputStream inputStream = urlConnection.getInputStream();
                StringBuffer buffer = new StringBuffer();
                if (inputStream == null) {
                    // Nothing to do.
                    bitcoinJsonStr = null;
                }
                reader = new BufferedReader(new InputStreamReader(inputStream));

                String line;
                while ((line = reader.readLine()) != null) {
                    // Since it's JSON, adding a newline isn't necessary (it won't affect parsing)
                    // But it does make debugging a *lot* easier if you print out the completed
                    // buffer for debugging.
                    buffer.append(line + "\n");
                }

                if (buffer.length() == 0) {
                    // Stream was empty.  No point in parsing.
                    bitcoinJsonStr = null;
                }
                bitcoinJsonStr = buffer.toString();
            } catch (IOException e) {
                Log.e("GetBitcoinPrice", "Error ", e);
                // If the code didn't successfully get the price index data, there's no point in attemping
                // to parse it.
                bitcoinJsonStr = null;
            } finally {
                if (urlConnection != null) {
                    urlConnection.disconnect();
                }
                if (reader != null) {
                    try {
                        reader.close();
                    } catch (final IOException e) {
                        Log.e("GetBitcoinPrice", "Error closing stream", e);
                    }
                }
            }
            if(this.mPrefIndex == "https://api.coindesk.com/v1/bpi/currentprice.json")
                return parseCoindesk(bitcoinJsonStr);
            else if (this.mPrefIndex == "https://api.coinbase.com/v2/prices/spot?currency=")
                return parseCoinbase(bitcoinJsonStr);
            else if (this.mPrefIndex == "https://www.okcoin.com/api/v1/ticker.do?symbol=")
                return parseOkcoin(bitcoinJsonStr);
            else if (this.mPrefIndex == "https://cex.io/api/ticker/BTC/")
                return parseCex(bitcoinJsonStr);
            else
                return 0.0;
        }
        private Double parseCex(String bitcoinJsonStr){
            Double price = 0.0;

            try {
                JSONObject obj = new JSONObject(bitcoinJsonStr);
                price = obj.getDouble("bid");
                Log.v("ConvertPriceStr", "Current Price is " + Double.toString(price));
                if (price == null){
                    Log.e("CEXParsing", "Parsed to Null");
                }

            }catch (JSONException x){
                Log.e("ConvertPriceStr", "Error Parsing bitcoinJsonStr");
            }
            return price;
        }
        private Double parseCoindesk(String bitcoinJsonStr){
            Double price = 0.0;

            try {
                JSONObject obj = new JSONObject(bitcoinJsonStr);
                JSONObject bpi = obj.getJSONObject("bpi");
                JSONObject usd = bpi.getJSONObject("USD");
                price = usd.getDouble("rate_float");
                Log.v("ConvertPriceStr", "Current Price is " + Double.toString(price));

            }catch (JSONException x){
                Log.e("ConvertPriceStr", "Error Parsing bitcoinJsonStr");
            }
            return price;
        }
        private Double parseCoinbase(String bitcoinJsonStr){
            Double price = 0.0;
            try{
                JSONObject obj = new JSONObject(bitcoinJsonStr);
                JSONObject bpi = obj.getJSONObject("data");
                price = bpi.getDouble("amount");
                Log.v("ParseCoinbase", "Current Price is " + Double.toString(price));
            }catch(JSONException e){
                Log.e("ParseCoinbase", "Error Parsing bitcoinJsonStr");
            }
            return price;
        }
        private Double parseOkcoin(String bitcoinJsonStr){
            Double price = 0.0;
            try{
                JSONObject obj = new JSONObject(bitcoinJsonStr);
                JSONObject bpi = obj.getJSONObject("ticker");
                price = bpi.getDouble("buy");
                Log.v("ParseOkCoin", "Current Price is " + Double.toString(price));
            }catch(JSONException e){
                Log.e("ParseOkCoin", "Error Parsing bitcoinJsonStr");
            }
            return price;
        }
        private String buildUrl(String prefFiat, String prefIndex){
            String url = null;
            try {
                if (prefIndex == "https://api.coinbase.com/v2/prices/spot?currency=") {
                    url = prefIndex + prefFiat;
                } else if (prefIndex == "https://api.coindesk.com/v1/bpi/currentprice.json") {
                    url = prefIndex + prefFiat;
                } else if (prefIndex == "https://www.okcoin.com/api/v1/ticker.do?symbol=") {
                    String modFiat;
                    modFiat = "btc_" + prefFiat;
                    url = prefIndex + modFiat;
                } else if (prefIndex == "https://cex.io/api/ticker/BTC/") {
                    String modFiat;
                    modFiat = prefIndex + prefFiat;
                    url = modFiat;
                } else {
                    url = "https://api.coindesk.com/v1/bpi/currentprice.json";
                }
            }catch(NullPointerException e){
                Log.e("URL Builder", "Error Constructing Proper URL", e);
            }
            return url;
        }

        protected void onPostExecute(Double result){
            setmBitcoinPriceOld(getmBitcoinPrice());
            setmBitcoinPrice(result);
        }
    }
}

XML Files:

activity_main.xml:

    <include
        layout="@layout/app_bar_main"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <android.support.design.widget.NavigationView
        android:id="@+id/nav_view"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:fitsSystemWindows="true"
        app:headerLayout="@layout/nav_header_main"
        app:menu="@menu/activity_main_drawer" />

</android.support.v4.widget.DrawerLayout>

app_bar_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context="com.instacoind.www.coind.MainActivity">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:popupTheme="@style/AppTheme.PopupOverlay" />

    </android.support.design.widget.AppBarLayout>

    <include layout="@layout/content_main" />

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        android:layout_margin="@dimen/fab_margin"
        android:src="@drawable/refresh_60_60" />

</android.support.design.widget.CoordinatorLayout>

content_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="com.instacoind.www.coind.MainActivity"
    tools:showIn="@layout/app_bar_main">

</RelativeLayout>

nav_header_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="@dimen/nav_header_height"
    android:background="@drawable/side_nav_bar"
    android:gravity="bottom"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:theme="@style/ThemeOverlay.AppCompat.Dark">

    <ImageView
        android:id="@+id/coin_display"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_alignParentStart="true"
        android:layout_alignParentLeft="true"
        android:paddingTop="@dimen/nav_header_vertical_spacing"
        android:src="@drawable/bitcoin_80_80"
        android:contentDescription="@string/coin_content_description"/>

    <TextView
        android:id="@+id/bpi_source_display"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:paddingTop="@dimen/nav_header_vertical_spacing"
        android:text="BPI_Source"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_alignParentBottom="true"
        android:textAppearance="@style/TextAppearance.AppCompat.Body1" />

    <TextView
        android:id="@+id/def_currency_display"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:paddingLeft="5dp"
        android:layout_toRightOf="@+id/bpi_source_display"
        android:layout_toEndOf="@+id/bpi_source_display"
        android:layout_alignParentBottom="true"
        android:text="DEF_Currency" />
    <TextView
        android:id="@+id/current_price_display"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:paddingTop="40dp"
        android:paddingStart="80dp"
        android:paddingLeft="80dp"
        android:layout_alignParentEnd="true"
        android:layout_alignParentRight="true"
        android:layout_toRightOf="@+id/coin_display"
        android:textAppearance="@style/TextAppearance.AppCompat.Headline"/>

</RelativeLayout>

Answer 1

I think the problem comes from these four method: parseCoindesk,parseCoinbase,parseCex,parseOkcoin

In each of these(parseCex for example):

            if (price == null){
                Log.e("CEXParsing", "Parsed to Null");// You just print a Log!
            }

        }catch (JSONException x){
            Log.e("ConvertPriceStr", "Error Parsing bitcoinJsonStr");
        }
        return price;//when price is null it can still return!
    }

so, you should try to return like this:

return price == null ? 0.0 : price;

Answer 2

Ok, way longer than I thought it would take till I could actually sit down and work on this again. Apologies for dragging my heels, I have fixed the problem of the crash.

It occurred because I was calling my refreshPriceDisplays() method before the onCreate/AsyncTask was finished. Once I moved refreshPriceDisplays() into my onPostExecute everything went great.

And as far as the first answer to this question you raised some good points about my logic and they have been addressed as well thank you so much for your inputs!