无法从 AS 中的 SQLite 数据库中获取数据

Question

我正在 Android Studio 中创建一个测验应用程序，因此我创建了一个包含问题的数据库。在助手 class 中，我有一个方法 getAllQuestions 将问题从数据库传输到数组列表，这样我就可以在 Main 中提取问题，在 Buttons 中提取 setText。但是，当我运行我的应用程序时，按钮和问题是空的，如果列表本身为空，应用程序不会抛出空指针等异常。

DB_Helper 方法：

private void addQuestions（问题数据库问题） {

    ContentValues cv =  new ContentValues();
    cv.put(QuestionTable.Column_Question,Questions.getQuestion());
    cv.put(QuestionTable.Column_Option1,Questions.getOption1());
    cv.put(QuestionTable.Column_Option2,Questions.getOption2());
    cv.put(QuestionTable.Column_Option3,Questions.getOption3());
    cv.put(QuestionTable.Column_Option4,Questions.getOption4());
    cv.put(QuestionTable.Column_Correct_Ans,Questions.getQuestion());
    db.insert(QuestionTable.Table_Name,null,cv);
}

public ArrayList getAllQuestions(){

    ArrayList<QuestionsDataBase> questionsList = new ArrayList<>();
    db = getReadableDatabase();
    String[] Projection ={
            QuestionTable._ID,
            QuestionTable.Column_Question,
            QuestionTable.Column_Option1,
            QuestionTable.Column_Option2,
            QuestionTable.Column_Option3,
            QuestionTable.Column_Option4,
            QuestionTable.Column_Correct_Ans
    };
    Cursor c = db.query(QuestionTable.Table_Name,
            Projection,
            null,
            null,
            null,
            null,
            null);
    if(c.moveToFirst()){
        do{
            QuestionsDataBase questions = new QuestionsDataBase();
            questions.setQuestion(c.getString(c.getColumnIndexOrThrow(QuestionTable.Column_Question)));
            questions.setOption1(c.getString(c.getColumnIndexOrThrow(QuestionTable.Column_Option1)));
            questions.setOption2(c.getString(c.getColumnIndexOrThrow(QuestionTable.Column_Option2)));
            questions.setOption3(c.getString(c.getColumnIndexOrThrow(QuestionTable.Column_Option3)));
            questions.setOption4(c.getString(c.getColumnIndexOrThrow(QuestionTable.Column_Option4)));
            questions.setCorrectAns(c.getInt(c.getColumnIndexOrThrow(QuestionTable.Column_Correct_Ans)));
            questionsList.add(questions);
            questionsList.add(questions);

        }while(c.moveToNext());
    }
    c.close();
    return questionsList;
}

MainActivity 中的方法：

私有无效 fecthDB(){

    DB_Helper db = new DB_Helper(this);
    questionList = db.getAllQuestions();
    startQuiz();
}

private void startQuiz() {

    questionTotalCount = questionList.size(); // the total amount of questions in the current quizactivity( is set to 10)
    Collections.shuffle(questionList); // shuffle the questions form the database that are stored in QuestionList
    showQuestions();

    nextbutton.setOnClickListener(view -> {
        if(!answered){
            if(option1.isChecked() || option2.isChecked() || option3.isChecked() || option4.isChecked())
                QuizOperations();
        }
    });

}

private void showQuestions() // 显示数据库中的问题和选项 {

    rbGroup.clearCheck();
    if(questionCounter< questionTotalCount) // if not all the questions yet answered set text to new questions
    {
        currentQuestions = questionList.get(questionCounter);
        questionCount.setText(currentQuestions.getQuestion());
        option1.setText(currentQuestions.getOption1());
        option2.setText(currentQuestions.getOption2());
        option3.setText(currentQuestions.getOption3());
        option4.setText(currentQuestions.getOption4());

        questionCounter ++; // +1 to question counter
        answered = false; // tye quiz is not yet completely answered while the current question is smaller then total
        nextbutton.setText("Next");

        questionCount.setText("Questions: " + questionCounter + "/" + questionTotalCount); // how many questions answered out of 10
    }
    else{// if all the questions are answered
        handler.postDelayed(() -> {
            Intent intent = new Intent(getApplicationContext(),QuizActivity.class); // open the next activity

        }, 500); // wait for a half second
    }
}

Answer 1

我相信您想在此处为 QuestionsDataBase 对象设置其他字段，而不是为数据库查询中的每一列设置 setQuestion()：

            questions.setQuestion(c.getString(c.getColumnIndexOrThrow(QuestionTable.Column_Option1)));
            questions.setQuestion(c.getString(c.getColumnIndexOrThrow(QuestionTable.Column_Option2)));
            questions.setQuestion(c.getString(c.getColumnIndexOrThrow(QuestionTable.Column_Option3)));
            questions.setQuestion(c.getString(c.getColumnIndexOrThrow(QuestionTable.Column_Option4)));
            questions.setQuestion(c.getString(c.getColumnIndexOrThrow(QuestionTable.Column_Correct_Ans)));

Thanks, edited it. Now it shows the options, but doesn't show the question itself.

您将文本设置为 questionCount 两次，后者会覆盖第一个。也许第一个应该改为设置问题文本视图。

无法从 AS 中的 SQLite 数据库中获取数据

Can't fetch data from SQLite database in AS

java

sqlite

android