java - 为什么将我的应用程序安装到其他设备后会出现 IndexOutOfBoundsException？

Question

为什么我会收到此错误？

Caused by: java.lang.IndexOutOfBoundsException: Invalid index 1, size is 0
at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:255)                                                                                   
at java.util.ArrayList.get(ArrayList.java:308)
at com.example.muhammad.exquizme.PlayQuizActivity.displayQuestion(PlayQuizActivity.java:109)
at com.example.muhammad.exquizme.PlayQuizActivity.onCreate(PlayQuizActivity.java:62)
at android.app.Activity.performCreate(Activity.java:6092)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1112)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2481)
 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2608) 
 at android.app.ActivityThread.access$800(ActivityThread.java:178) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1470) 
at android.os.Handler.dispatchMessage(Handler.java:111) 
at android.os.Looper.loop(Looper.java:194) 
at android.app.ActivityThread.main(ActivityThread.java:5637) 
 at java.lang.reflect.Method.invoke(Native Method) 
 at java.lang.reflect.Method.invoke(Method.java:372) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:959) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:754) 

我的手机中已经出现此错误，并且已修复。然后我尝试在平板电脑设备中安装我的应用程序并运行它。当我按下按钮导航到 PlayQuizActivity 时，它崩溃了，并显示Caused by: java.lang.IndexOutOfBoundsException: Invalid index 1, size is 0。

这是PlayQuizActivity.java的代码:

公共(public)类 PlayQuizActivity 扩展了 AppCompatActivity {

private static final String QUESTION_MANAGER_URL = "http://mbcatubig.net16.net/ExQuiz%20Me/Quiz_Manager.php";
private int randomIndex, questionIndex = 1;
private SQLiteDatabaseHelper questionDatabase;
private RadioButton choiceBtnA, choiceBtnB, choiceBtnC, choiceBtnD;
private TextView questionTextView, qIndexView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_play_quiz);
    //questionDatabase = new SQLiteDatabaseHelper(this);

    qIndexView = (TextView) findViewById(R.id.currentNumber);
    questionTextView = (TextView) findViewById(R.id.questionTextView);
    choiceBtnA = (RadioButton) findViewById(R.id.choiceA);
    choiceBtnB = (RadioButton) findViewById(R.id.choiceB);
    choiceBtnC = (RadioButton) findViewById(R.id.choiceC);
    choiceBtnD = (RadioButton) findViewById(R.id.choiceD);

    //Get Network State
    ConnectivityManager connectivity = (ConnectivityManager) this.getSystemService(Context.CONNECTIVITY_SERVICE);
    boolean isConnected = false;
    if (connectivity != null) {
        NetworkInfo info = connectivity.getActiveNetworkInfo();
        if (info != null && info.isConnected()) {
            isConnected = true;
        }
    }

    if (isConnected) {
        getJSONFromURL();
        displayQuestion();
    } else {
        displayQuestion();
    }


    choiceBtnA.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            checkAnswers(0);
        }
    });

    choiceBtnB.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            checkAnswers(1);
        }
    });

    choiceBtnC.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            checkAnswers(2);
        }
    });

    choiceBtnD.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            checkAnswers(3);
        }
    });
}

private void displayQuestion() {

    qIndexView.setText("QUESTION " + questionIndex++ + " /10");
    randomIndex = new Random().nextInt(10);
    questionDatabase = new SQLiteDatabaseHelper(this);

    //Uncheck button
    choiceBtnA.setChecked(false);
    choiceBtnB.setChecked(false);
    choiceBtnC.setChecked(false);
    choiceBtnD.setChecked(false);
    if (questionIndex <= 10) {
        String question = questionDatabase.getQuestions().get(randomIndex).question; //this causes the error
        String[] choices = new String[4];
        choices[0] = questionDatabase.getQuestions().get(randomIndex).choices[0];
        choices[1] = questionDatabase.getQuestions().get(randomIndex).choices[1];
        choices[2] = questionDatabase.getQuestions().get(randomIndex).choices[2];
        choices[3] = questionDatabase.getQuestions().get(randomIndex).choices[3];
        questionTextView.setText(question);
        choiceBtnA.setText(choices[0]);
        choiceBtnB.setText(choices[1]);
        choiceBtnC.setText(choices[2]);
        choiceBtnD.setText(choices[3]);
    }
}

private void checkAnswers(int index) {
    String answer = questionDatabase.getQuestions().get(randomIndex).choices[index], correctAnswer = questionDatabase.getQuestions().get(randomIndex).answer;
    if (answer.equals(correctAnswer)) {
        Toast.makeText(PlayQuizActivity.this, "Correct", Toast.LENGTH_SHORT).show();
        final Handler handler = new Handler();
        handler.postDelayed(new Runnable() {
            @Override
            public void run() {
                displayQuestion();
            }
        }, 2000);
        //Log.d("Is it correct?", "Correct");
    } else {
        Toast.makeText(PlayQuizActivity.this, "Incorrect", Toast.LENGTH_SHORT).show();
        final Handler handler = new Handler();
        handler.postDelayed(new Runnable() {
            @Override
            public void run() {
                displayQuestion();
            }
        }, 2000);
        //Log.d("Is it correct?", "Incorrect");
    }
}

private void getJSONFromURL() {
    class QuestionExtractorTask extends AsyncTask<Void, Void, String> {
        ProgressDialog loading;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            loading = ProgressDialog.show(PlayQuizActivity.this, "Loading questions...", null, true, true);
        }

        @Override
        protected String doInBackground(Void... params) {

            BufferedReader bufferedReader;
            try {
                URL url = new URL(QUESTION_MANAGER_URL);
                HttpURLConnection con = (HttpURLConnection) url.openConnection();
                StringBuilder sb = new StringBuilder();

                bufferedReader = new BufferedReader(new InputStreamReader(con.getInputStream()));

                String json;
                while ((json = bufferedReader.readLine()) != null) {
                    sb.append(json + "\n");
                }
                json = sb.toString().trim();

                return json;

            } catch (Exception e) {
                return null;
            }

        }

        @Override
        protected void onPostExecute(String jsonData) {
            super.onPostExecute(jsonData);
            loading.dismiss();
            QuestionJSONParser questionJsonParser = new QuestionJSONParser();
            questionJsonParser.extractJSON(jsonData);
        }
    }
    QuestionExtractorTask questionExtractorTask = new QuestionExtractorTask();
    questionExtractorTask.execute();
}


class QuestionJSONParser {
    private static final String ROOT_OBJECT = "questions", QUESTION = "question", CHOICES = "choices", CATEGORY = "category";

    public void extractJSON(String jsonData) {
        try {
            //Get the questions object
            JSONObject questions = new JSONObject(jsonData).getJSONObject(ROOT_OBJECT);
            //Get the questions' objects
            Collections.shuffle(uniqueRandomNumber(questions.length()));
            for (int counter = 0; counter < 10; counter++) {
                String[] choices = new String[4];


                System.out.println(uniqueRandomNumber(questions.length()));

                JSONObject theQuestionObject = questions.getJSONObject(uniqueRandomNumber(questions.length()).get(counter) + "");
                String question = theQuestionObject.getString(QUESTION), category = theQuestionObject.getString(CATEGORY), correctAnswer = "";

                //Log.d("question", question);
                JSONArray theChoicesArray = theQuestionObject.getJSONArray(CHOICES);

                //Get choice object from the choices object
                for (int i = 0; i < theChoicesArray.length(); i++) {
                    JSONObject choiceObject = theChoicesArray.getJSONObject(i);
                    choices[i] = choiceObject.optString("choice");
                    if (choiceObject.getInt("is_correct_choice") == 1) {
                        correctAnswer = choices[i];
                    }
                }
                //add in SQLite Database
                questionDatabase = new SQLiteDatabaseHelper(getApplicationContext());
                questionDatabase.addQuestion(new QuizQuestion(question, choices, correctAnswer, category));
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }

    public List uniqueRandomNumber(int length) {

        if (length != 0) {
            Integer[] arr = new Integer[length];
            for (int i = 0; i < arr.length; i++) {
                arr[i] = i + 1;
            }
            return Arrays.asList(arr);
        }
        return null;
    }

}

}

我正在尝试找出解决此问题的方法。我考虑过一些导致错误的可能性。我想当从 url 中提取 json 然后解析它时，也许它不会将这些数据保存到我的 sqlite 数据库中，但这个问题已经解决了，所以我不知道这是如何发生的。它总是说尺寸是0。这是否意味着我需要坚持使用我的手机。我想这与sdk版本无关，不是吗？

这是我的SQLiteDatabaseHelper.class:

类 SQLiteDatabaseHelper 扩展 SQLiteOpenHelper {

private static final String[] TABLES = new String[]{"question", "question_choices", "stats"};

public SQLiteDatabaseHelper(Context context) {
    super(context, "QUESTION_DATABASE", null, 1);
}

@Override
public void onCreate(SQLiteDatabase db) {

    //Create Questions Table
    String CREATE_QUESTIONS_TABLE = "CREATE TABLE " + TABLES[0] + " (\n" +
            "  quiz_question_id INT  PRIMARY KEY,\n" +
            "  question TEXT ,\n" +
            "  choice_a TEXT,\n" +
            "  choice_b TEXT ,\n" +
            "  choice_c TEXT ,\n" +
            "  choice_d TEXT ,\n" +
            "  answer TEXT ,\n" +
            "   category TEXT)";
    db.execSQL(CREATE_QUESTIONS_TABLE);
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    db.execSQL("DROP TABLE IF EXISTS" + TABLES[0]);
    db.execSQL("DROP TABLE IF EXISTS" + TABLES[2]);
}

//Managing question for the quiz
public void addQuestion(QuizQuestion questions) {
    SQLiteDatabase db = this.getWritableDatabase();

    //Insert in question table
    ContentValues values = new ContentValues();
    values.put("question", questions.question);
    values.put("choice_a", questions.choices[0]);
    values.put("choice_b", questions.choices[1]);
    values.put("choice_c", questions.choices[2]);
    values.put("choice_d", questions.choices[3]);
    values.put("answer", questions.answer);
    values.put("category", questions.category);

    // Inserting Row
    db.insert(TABLES[0], null, values);
    db.close(); // Closing database connection
}

//Managing best scores and best category for stats

public List<QuizQuestion> getQuestions() {
    List<QuizQuestion> quizQuestionArrayList = new ArrayList<>();
    String selectQuery = "SELECT * FROM " + TABLES[0];
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.rawQuery(selectQuery, null);
    if (!cursor.isLast()) {
        while (cursor.moveToNext()) {
            //Log.d("cursor.getString(1)", cursor.getString(1));
            String[] choices = {cursor.getString(2), cursor.getString(3), cursor.getString(4), cursor.getString(5)};
            quizQuestionArrayList.add(new QuizQuestion(cursor.getString(1), choices, cursor.getString(6), cursor.getString(7)));
        }
    }

    db.close();
    return quizQuestionArrayList;
}

}

上面的代码处理 sqlite 数据库。如果我连接到互联网，我基本上想要在这里完成的任务是，它会将数据下载到我的 sqlite 数据库中，这样当它离线时，就可以访问它。我的手机上已经发生过这种情况，但在我的平板电脑上，它无法正常工作，如上面的错误所示。如果您需要更多详细信息，请告诉我。任何帮助表示赞赏。谢谢。

Answer 1

在我看来，你的数据库是空的。数据库助手的 onCreate 创建了一个表，但它从不向其中添加任何内容。

您的网络代码也不正确 - 您调用

    getJSONFromURL();
    displayQuestion();

但是 getJsonFromUrl 启动了一个异步任务。您不希望在任务完成之前调用 displayQuestion。 displayQuestion 只能在 onPostExecute 中调用，或者在过去下载过数据的情况下调用。