Android应用程序崩溃一旦重新打开

Question

I'm not only new to Android Studio, I'm new to programming in general (I've been slowly teaching myself what I can the past year or so as a hobby).

I've run into an issue with my Android app that I can't find an answer to - even though I know many people have asked similar questions, I can't seem to understand the solution enough to adapt it to my particular problem. When compiled, my app will run fine and does everything I want it to do "correctly" (except for a small thing with the toolbar but I'll get to that later haha).

The one thing it does NOT do is open correctly after I've closed it. I can go to the home screen and back to the app, but if I close the app altogether and try to reopen is says it "keeps stopping."

Now, I think it would be useful to give you my code (there are only two activities in this app) and my "logcat". However, I'm currently trying to read-up and understand how to retrieve my "logcat" in the first place haha so hopefully I'll have that here soon.

From my readings my understanding is that my problem is either with the global variables I'm declaring or something with the button ID's when I make buttons dynamically. I run into people having issues with their "Threads" but I'm having trouble connecting that to my particular position. However, if any of these are the issue, I'm having a hard time understanding what the issue actually is.

Here's my main activity...

package com.example.getcoins;

import android.content.Intent;
import android.icu.text.DecimalFormat;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.TextView;

import com.jjoe64.graphview.GraphView;
import com.jjoe64.graphview.series.DataPoint;
import com.jjoe64.graphview.series.PointsGraphSeries;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {

    int intialCoins = 21;
    int coins;
    int buttonColor =  android.graphics.Color.rgb(0, 150, 150);
    int textColor =  android.graphics.Color.rgb(255, 255, 255);
    ArrayList<Integer> coinsOverTime = new ArrayList<Integer>();

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

        Intent intent = getIntent();
        coins = intent.getIntExtra("COINS", 1);

        if (intent.getExtras() != null)
        {
            Boolean winner = intent.getBooleanExtra("WINNER", true);
            int gambleamount = intent.getIntExtra("GAMBLE", 1);
            Bundle bundle = intent.getExtras();
            coinsOverTime = bundle.getIntegerArrayList("COIN_HISTORY");

            if (winner == true)
            {
                coins = coins + gambleamount;
                coinsOverTime.add(coins);
            }

            if (winner == false && gambleamount == 1)
            {
                coins = coins;
                coinsOverTime.add(coins);
            }

            else if(winner == false)
            {
                coins = coins - gambleamount;
                coinsOverTime.add(coins);
            }
        }

        else
        {
            coins = intialCoins;
            coinsOverTime.add(coins);
        }

        String number = Integer.toString(coins);
        double amount = Double.parseDouble(number);
        DecimalFormat formatter = new DecimalFormat("#,###");
        String formatted = formatter.format(amount);

        TextView textView = (TextView) findViewById(R.id.textView);
        textView.setText(formatted);

        GraphView graph = (GraphView) findViewById(R.id.graph);
        PointsGraphSeries<DataPoint> series = new PointsGraphSeries<>(generateData());
        graph.addSeries(series);
        series.setShape(PointsGraphSeries.Shape.POINT);
        graph.getViewport().setXAxisBoundsManual(true);
        graph.getViewport().setMinX(0);
        graph.getViewport().setMaxX(coinsOverTime.size());

        if (coins >= 0 && coins < 101)
        {
            Button getCoinButton = addButton("Get 1 coin");
            getCoinButton.setId(R.id.one);
            getCoinButton.setOnClickListener(new View.OnClickListener() {
                public void onClick(View v) {
                    getOneCoin(v);
                }
            });
        }

        if (coins >= 11 && coins < 501)
        {
            Button getCoinButton = addButton("Get 10 coins");
            getCoinButton.setId(R.id.ten);
            getCoinButton.setOnClickListener(new View.OnClickListener() {
                public void onClick(View v) {
                    getTenCoins(v);
                }
            });
        }

        if (coins >= 21 && coins < 2001)
        {
            Button getCoinButton = addButton("Get 20 coins");
            getCoinButton.setId(R.id.twenty);
            getCoinButton.setOnClickListener(new View.OnClickListener() {
                public void onClick(View v) {
                    getTwentyCoins(v);
                }
            });
        }

        if (coins >= 101 && coins < 5001)
        {
            Button getCoinButton = addButton("Get 100 coins");
            getCoinButton.setId(R.id.one_hundred);
            getCoinButton.setOnClickListener(new View.OnClickListener() {
                public void onClick(View v) {
                    getOneHundredCoins(v);
                }
            });
        }

        if (coins >= 501 && coins < 10001)
        {
            Button getCoinButton = addButton("Get 500 coins");
            getCoinButton.setId(R.id.five_hundred);
            getCoinButton.setOnClickListener(new View.OnClickListener() {
                public void onClick(View v) {
                    getFiveHundredCoins(v);
                }
            });
        }

        if (coins >= 2001)
        {
            Button getCoinButton = addButton("Get 2,000 coins");
            getCoinButton.setId(R.id.two_thousand);
            getCoinButton.setOnClickListener(new View.OnClickListener() {
                public void onClick(View v) {
                    getTwoThousandCoins(v);
                }
            });
        }

        if (coins >= 5001)
        {
            Button getCoinButton = addButton("Get 5,000 coins");
            getCoinButton.setId(R.id.five_thousand);
            getCoinButton.setOnClickListener(new View.OnClickListener() {
                public void onClick(View v) {
                    getFiveThousandCoins(v);
                }
            });
        }

        if (coins >= 10001)
        {
            Button getCoinButton = addButton("Get 10,000 coins");
            getCoinButton.setId(R.id.ten_thousand);
            getCoinButton.setOnClickListener(new View.OnClickListener() {
                public void onClick(View v) {
                    getTenThousandCoins(v);
                }
            });
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.action_items, menu);
        return true;
    }

    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.rules:
                // User chose the "Settings" item, show the app settings UI...
                return true;

            case R.id.action_settings:
                // User chose the "Favorite" action, mark the current item
                // as a favorite...
                return true;

            case android.R.id.home:
                return true;

            default:
                // If we got here, the user's action was not recognized.
                // Invoke the superclass to handle it.
                return super.onOptionsItemSelected(item);
        }
    }




    public void getOneCoin(View view){
        Intent intent = new Intent(this, gamble.class);
        Bundle bundle = new Bundle();
        bundle.putIntegerArrayList("COIN_HISTORY", coinsOverTime);
        intent.putExtra("GAMBLE", 1);
        intent.putExtra("COINS", coins);
        intent.putExtras(bundle);
        startActivity(intent);
    }

    public void getTenCoins(View view){
        Intent intent = new Intent(this, gamble.class);
        Bundle bundle = new Bundle();
        bundle.putIntegerArrayList("COIN_HISTORY", coinsOverTime);
        intent.putExtra("GAMBLE", 10);
        intent.putExtra("COINS", coins);
        intent.putExtras(bundle);
        startActivity(intent);
    }

    public void getTwentyCoins(View view){
        Intent intent = new Intent(this, gamble.class);
        Bundle bundle = new Bundle();
        bundle.putIntegerArrayList("COIN_HISTORY", coinsOverTime);
        intent.putExtra("GAMBLE", 20);
        intent.putExtra("COINS", coins);
        intent.putExtras(bundle);
        startActivity(intent);
    }

    public void getOneHundredCoins(View view){
        Intent intent = new Intent(this, gamble.class);
        Bundle bundle = new Bundle();
        bundle.putIntegerArrayList("COIN_HISTORY", coinsOverTime);
        intent.putExtra("GAMBLE", 100);
        intent.putExtra("COINS", coins);
        intent.putExtras(bundle);
        startActivity(intent);
    }

    public void getFiveHundredCoins(View view){
        Intent intent = new Intent(this, gamble.class);
        Bundle bundle = new Bundle();
        bundle.putIntegerArrayList("COIN_HISTORY", coinsOverTime);
        intent.putExtra("GAMBLE", 500);
        intent.putExtra("COINS", coins);
        intent.putExtras(bundle);
        startActivity(intent);
    }

    public void getTwoThousandCoins(View view){
        Intent intent = new Intent(this, gamble.class);
        Bundle bundle = new Bundle();
        bundle.putIntegerArrayList("COIN_HISTORY", coinsOverTime);
        intent.putExtra("GAMBLE", 2000);
        intent.putExtra("COINS", coins);
        intent.putExtras(bundle);
        startActivity(intent);
    }

    public void getFiveThousandCoins(View view){
        Intent intent = new Intent(this, gamble.class);
        Bundle bundle = new Bundle();
        bundle.putIntegerArrayList("COIN_HISTORY", coinsOverTime);
        intent.putExtra("GAMBLE", 5000);
        intent.putExtra("COINS", coins);
        intent.putExtras(bundle);
        startActivity(intent);
    }

    public void getTenThousandCoins(View view){
        Intent intent = new Intent(this, gamble.class);
        Bundle bundle = new Bundle();
        bundle.putIntegerArrayList("COIN_HISTORY", coinsOverTime);
        intent.putExtra("GAMBLE", 10000);
        intent.putExtra("COINS", coins);
        intent.putExtras(bundle);
        startActivity(intent);
    }

    public Button addButton(String name)
    {
        LinearLayout linearLayout = (LinearLayout) findViewById(R.id.linearLayout);
        Button newCoinButton = new Button(this);
        newCoinButton.setText(name);
        newCoinButton.setTextSize(30);
        //newCoinButton.setBackgroundColor(buttonColor);
        newCoinButton.setTextColor(textColor);
        //newCoinButton.setLayoutParams(new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.WRAP_CONTENT));
        linearLayout.addView(newCoinButton);

        return newCoinButton;
    }

    public DataPoint[] generateData()
    {
        int size = coinsOverTime.size();
        DataPoint[] values = new DataPoint[size];
        for (int i=0; i<size; i++)
        {
            int y1 = coinsOverTime.get(i);
            DataPoint v = new DataPoint(i, y1);
            values[i] = v;
        }

        return values;
    }
}

and here's the Gamble activity it talks to...

package com.example.getcoins;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.ActionBar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.View;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.Collections;

public class gamble extends AppCompatActivity {

    ArrayList<Integer> buttonValues = getButtonValues();
    //ArrayList<Integer> coinHistory = getCoinHistory();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_gamble);
        Toolbar myToolbar = (Toolbar) findViewById(R.id.my_toolbar);
        setSupportActionBar(myToolbar);
        ActionBar ab = getSupportActionBar();
        ab.setDisplayHomeAsUpEnabled(false);

        TextView textViewLeft = (TextView) findViewById(R.id.textView2);
        TextView textViewRight = (TextView) findViewById(R.id.textView3);
        TextView textViewCoins = (TextView) findViewById(R.id.textView4);

        textViewCoins.setText("Good Luck!");


        if (buttonValues.get(0) == 0)
        {
            textViewLeft.setText("Winner");
        }

        else
        {
            textViewLeft.setText("Loser");
        }

        if (buttonValues.get(1) == 0)
        {
            textViewRight.setText("Winner");
        }

        else
        {
            textViewRight.setText("Loser");
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.action_items, menu);
        return true;
    }

    public ArrayList<Integer> getButtonValues()
    {
        ArrayList<Integer> buttonvalues = new ArrayList<Integer>();
        buttonvalues.add(0);
        buttonvalues.add(1);
        Collections.shuffle(buttonvalues);
        return buttonvalues;
    }

    public void leftButtonClick(View view)
    {
        if (buttonValues.get(0) == 0)
        {
           winner();
        }

        else
        {
            loser();
        }
    }

    public void rightButtonClick(View view)
    {
        if (buttonValues.get(1) == 0)
        {
            winner();
        }

        else
        {
            loser();
        }
    }

    public void winner()
    {
        Intent oldintent = getIntent();
        Bundle oldbundle = oldintent.getExtras();
        int gambleamount = oldintent.getIntExtra("GAMBLE", 1);
        int coins = oldintent.getIntExtra("COINS", 1);
        ArrayList<Integer> coinHistory = oldbundle.getIntegerArrayList("COIN_HISTORY");

        Intent intent = new Intent(this, MainActivity.class);
        Bundle bundle = new Bundle();
        bundle.putIntegerArrayList("COIN_HISTORY", coinHistory);
        intent.putExtra("WINNER", true);
        intent.putExtra("GAMBLE", gambleamount);
        intent.putExtra("COINS", coins);
        intent.putExtras(bundle);
        startActivity(intent);
    }

    public void loser()
    {
        Intent oldintent = getIntent();
        Bundle oldbundle = oldintent.getExtras();
        int gambleamount = oldintent.getIntExtra("GAMBLE", 1);
        int coins = oldintent.getIntExtra("COINS", 1);
        ArrayList<Integer> coinHistory = oldbundle.getIntegerArrayList("COIN_HISTORY");

        Intent intent = new Intent(this, MainActivity.class);
        Bundle bundle = new Bundle();
        bundle.putIntegerArrayList("COIN_HISTORY", coinHistory);
        intent.putExtra("WINNER", false);
        intent.putExtra("GAMBLE", gambleamount);
        intent.putExtra("COINS", coins);
        intent.putExtras(bundle);
        startActivity(intent);
    }
}

I appreciate any help anyone may be able to provide.

Luke

UPDATE: Here's my logcat...or at least what I believe is the relevant portion. I grabbed the text it gave me once the crash happened.

04-06 16:10:39.091 3897-3897/? I/art: Late-enabling -Xcheck:jni
04-06 16:10:39.322 3897-3897/com.example.getcoins W/System: ClassLoader referenced unknown path: /data/app/com.example.getcoins-1/lib/arm64
04-06 16:10:39.363 3897-3897/com.example.getcoins I/InstantRun: Starting Instant Run Server for com.example.getcoins
04-06 16:10:42.158 3897-3897/com.example.getcoins W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
04-06 16:10:42.643 3897-3897/com.example.getcoins D/AndroidRuntime: Shutting down VM
04-06 16:10:42.645 3897-3897/com.example.getcoins E/AndroidRuntime: FATAL EXCEPTION: main
                                                                    Process: com.example.getcoins, PID: 3897
                                                                    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.getcoins/com.example.getcoins.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.util.ArrayList.add(java.lang.Object)' on a null object reference
                                                                        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2671)
                                                                        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2736)
                                                                        at android.app.ActivityThread.-wrap12(ActivityThread.java)
                                                                        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1478)
                                                                        at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                        at android.os.Looper.loop(Looper.java:154)
                                                                        at android.app.ActivityThread.main(ActivityThread.java:6154)
                                                                        at java.lang.reflect.Method.invoke(Native Method)
                                                                        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
                                                                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:757)
                                                                     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.util.ArrayList.add(java.lang.Object)' on a null object reference
                                                                        at com.example.getcoins.MainActivity.onCreate(MainActivity.java:50)
                                                                        at android.app.Activity.performCreate(Activity.java:6683)
                                                                        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1140)
                                                                        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2624)
                                                                        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2736) 
                                                                        at android.app.ActivityThread.-wrap12(ActivityThread.java) 
                                                                        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1478) 
                                                                        at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                        at android.os.Looper.loop(Looper.java:154) 
                                                                        at android.app.ActivityThread.main(ActivityThread.java:6154) 
                                                                        at java.lang.reflect.Method.invoke(Native Method) 
                                                                        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867) 
                                                                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:757) 

UPDATE:

First off, thank you for your responses! This has been very educational for me! I'd like to run by my current logic of what I think is going on to see if I'm on the right track. It seems like when the app is first compiled onto my phone, everything is okay (ie the global variables in main activity are seen and dealt with correctly).

However, after looking at the link Pavel B. suggested I look at, it seems that through this process... A simplified illustration of the activity lifecycle.

...once I kill the app and open it back up, it goes straight to the onCreate() method (and seems to have skipped the global variables defined above it). Is this what is going on?

I have voted up comments I have found helpful but it says since my reputation is less than 15 it won't be public.

Thank you again SO much!!

Luke

Answer 1

this may or may not solve your issue, but when you call your 'gamble' activity from your main activity, you should be using startActivityForResult() and register a callback receiver to handle the result...

ie you're currently 'starting' your main activity over itself instead of just passing results back to it via setResult

see:

https://developer.android.com/training/basics/intents/result.html

and

https://developer.android.com/reference/android/os/ResultReceiver.html

UPDATE:

consider creating a static final request code you can use:

public static final int REQUEST_CODE_GAMBLE = 172;

change your getCoin methods to startActivityForResult(), using your static request code:

public void getOneCoin(View view){
    Intent intent = new Intent(this, gamble.class);
    Bundle bundle = new Bundle();
    bundle.putIntegerArrayList("COIN_HISTORY", coinsOverTime);
    intent.putExtra("GAMBLE", 1);
    intent.putExtra("COINS", coins);
    intent.putExtras(bundle);
    startActivityForResult(intent, REQUEST_CODE_GAMBLE);
}

then override onActivityResult() in your MainActivity:

@Override
protected void onActivityResult(final int requestCode, final int resultCode, final Intent intent){
super.onActivityResult(requestCode, resultCode, intent);
    if(requestCode == REQUEST_CODE_GAMBLE){
        if(resultCode == RESULT_OK){

            //do all that same stuff you were doing in onCreate() in your MainActivity
            //i.e. :
            coins = intent.getIntExtra("COINS", 1);
            //etc

        }
    }


}

then in your winner() and loser() methods in the gamble activity, simply set the result and call finish():

public void winner()
{
    Intent oldintent = getIntent();
    Bundle oldbundle = oldintent.getExtras();
    int gambleamount = oldintent.getIntExtra("GAMBLE", 1);
    int coins = oldintent.getIntExtra("COINS", 1);
    ArrayList<Integer> coinHistory = oldbundle.getIntegerArrayList("COIN_HISTORY");
    Intent intent = new Intent();
    Bundle bundle = new Bundle();
    bundle.putIntegerArrayList("COIN_HISTORY", coinHistory);
    intent.putExtra("WINNER", true);
    intent.putExtra("GAMBLE", gambleamount);
    intent.putExtra("COINS", coins);
    intent.putExtras(bundle);
    getParent().setResult(Activity.RESULT_OK, intent);
    finish();
}

When your gamble activity "finishes", it will send all that intent data to your MainActivity's new onActivityResult() method, and you can do with it what you'd like there

Answer 2

It seems that the error is that Your coinsOverTime array is null. It works fine when Your activity is started with an intent in which this array is stored as an extra, but this is not the case when your app is going off screen and returning.

When You are pressing home, Your activity should save its state and restore it as it comes back on screen. Pls read Saving and restoring activity state section here: https://developer.android.com/guide/components/activities/activity-lifecycle.html

Answer 3

Just put if(coinsOverTime != null) before coinsOverTime.add(coins); every where. This crash happens because the coinsOverTime array is Null pointer when your activity be resumed.