使用 SQLite 数据库时我的活动不会打开

Question

目前正在关注有关集成 SQLite 的 Android 测验应用的 YouTube 教程。链接在这里：https://www.youtube.com/watch?v=pEDVdSUuWXE

我一直在关注他的细节，但是当我在 Android Studio 的模拟器上启动我的应用程序时，当我按下启动 Activity 上的按钮时，预期的 Activity 不会启动。此外，我的 SQLite 数据库不会使用 QuizActivity Java 类将硬编码的数据插入其中。

这是我的代码

QuizDBHelper.java

package com.faith.mobilequiz;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import com.faith.mobilequiz.QuizContract.*;

import java.util.ArrayList;
import java.util.List;

public class QuizDBHelper extends SQLiteOpenHelper {
    private static final String DATABASE_NAME = "MobileQuiz.db";
    private static final int DATABASE_VERSION = 1;

    private SQLiteDatabase db;

     public QuizDBHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
         this.db = db;

        final String SQL_CREATE_QUESTIONS_TABLE = "CREATE TABLE " +
                QuestionsTable.TABLE_NAME + " ( " +
                QuestionsTable._ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
                QuestionsTable.COLUMN_QUESTION + " TEXT, " +
                QuestionsTable.COLUMN_OPTION1 + " TEXT, " +
                QuestionsTable.COLUMN_OPTION2 + " TEXT, " +
                QuestionsTable.COLUMN_OPTION3 + " TEXT, " +
                QuestionsTable.COLUMN_ANSWER_NUMBER + " INTEGER " +
                ")";

         db.execSQL(SQL_CREATE_QUESTIONS_TABLE);
         fillQuestionsTable();

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
          db.execSQL("DROP TABLE IF EXISTS " + QuestionsTable.TABLE_NAME);
          onCreate(db);
    }

    private void fillQuestionsTable() {
        Question q1 = new Question("A is correct", "A", "B", "C", 1);
        addQuestion(q1);
        Question q2 = new Question("B is correct", "A", "B", "C", 2);
        addQuestion(q2);
        Question q3 = new Question("C is correct", "A", "B", "C", 3);
        addQuestion(q3);
        Question q4 = new Question("A is correct again", "A", "B", "C", 1);
        addQuestion(q4);
        Question q5 = new Question("B is correct again", "A", "B", "C", 2);
        addQuestion(q5);
    }

    private void addQuestion(Question question) {
        ContentValues cv = new ContentValues();
        cv.put(QuestionsTable.COLUMN_QUESTION, question.getQuestion());
        cv.put(QuestionsTable.COLUMN_OPTION1, question.getOption1());
        cv.put(QuestionsTable.COLUMN_OPTION2, question.getOption2());
        cv.put(QuestionsTable.COLUMN_OPTION3, question.getOption3());
        cv.put(QuestionsTable.COLUMN_ANSWER_NUMBER, question.getAnswerNum());
        db.insert(QuestionsTable.TABLE_NAME, null, cv);
    }

    public List<Question> getAllQuestions() {
         List<Question> questionList = new ArrayList<>();
         db = getReadableDatabase();
         Cursor c = db.rawQuery("SELECT * FROM " + QuestionsTable.TABLE_NAME, null);

         if(c.moveToFirst()) {
             do {
                 Question question = new Question();
                 question.setQuestion(c.getString(c.getColumnIndex(QuestionsTable.COLUMN_QUESTION)));
                 question.setOption1(c.getString(c.getColumnIndex(QuestionsTable.COLUMN_OPTION1)));
                 question.setOption2(c.getString(c.getColumnIndex(QuestionsTable.COLUMN_OPTION2)));
                 question.setOption3(c.getString(c.getColumnIndex(QuestionsTable.COLUMN_OPTION3)));
                 question.setAnswerNum(c.getInt(c.getColumnIndex(QuestionsTable.COLUMN_ANSWER_NUMBER)));
                 questionList.add(question);
             } while(c.moveToNext());
         }

         c.close();
         return questionList;


    }
}

这是 QuizActivity.java

package com.faith.mobilequiz;

import android.content.res.ColorStateList;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.Button;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.TextView;

import java.util.Collections;
import java.util.List;

public class QuizActivity extends AppCompatActivity {
    private TextView textViewQuestion;
    private TextView textViewScore;
    private TextView textViewQuestionCount;
    private TextView textViewTimer;
    private RadioGroup rbGroup;
    private RadioButton rb1;
    private RadioButton rb2;
    private RadioButton rb3;
    private Button buttonConfirmNext;

    private ColorStateList textColorDefaultRb;

    private List<Question> questionList;
    private int questionCounter;
    private int questionCountTotal;
    private Question currentQuestion;

    private int score;
    private boolean answered;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_quiz);

        textViewQuestion = findViewById(R.id.txtQuestion);
        textViewScore = findViewById(R.id.txtScore);
        textViewQuestionCount = findViewById(R.id.txtQuestionCount);
        textViewTimer = findViewById(R.id.txtTimer);
        rbGroup = findViewById(R.id.radioGroup);
        rb1 = findViewById(R.id.radioBtn1);
        rb2 = findViewById(R.id.radioBtn2);
        rb3 = findViewById(R.id.radioBtn3);
        buttonConfirmNext = findViewById(R.id.btnConfirmNext);

        textColorDefaultRb = rb1.getTextColors();

        QuizDBHelper dbHelper = new QuizDBHelper(this);
        questionList = dbHelper.getAllQuestions();
        questionCountTotal = questionList.size();
        Collections.shuffle(questionList);

        showNextQuestion();

    }

    private void showNextQuestion() {
        rb1.setTextColor(textColorDefaultRb);
        rb2.setTextColor(textColorDefaultRb);
        rb3.setTextColor(textColorDefaultRb);
        rbGroup.clearCheck();

        if(questionCounter < questionCountTotal) {
            currentQuestion = questionList.get(questionCounter);

            textViewQuestion.setText(currentQuestion.getQuestion());
            rb1.setText(currentQuestion.getOption1());
            rb2.setText(currentQuestion.getOption2());
            rb3.setText(currentQuestion.getOption3());
            questionCounter++;
            textViewQuestionCount.setText("Question: " + questionCounter + "/" + questionCountTotal);
            answered = false;
            buttonConfirmNext.setText("Confirm");

        } else {
            finishQuiz();
        }
    }

    private void finishQuiz() {
        finish();
    }
}

查询有问题吗？

Answer 1

查询有问题吗？

没有。

复制和测试的代码很好。

使用仅由一个按钮组成的 MainActivity 活动，可以单击该按钮以启动测验活动，从而启动带有问题的测验活动。

使用后退按钮返回主活动并单击按钮显示下一个问题。

在我的主要活动中：-

public class MainActivity extends AppCompatActivity {
    Button mQuizButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
        mQuizButton = this.findViewById(R.id.quizbutton);
        mQuizButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent i = new Intent(MainActivity.this,QuizActivity.class);
                startActivity(i);
            }
        });
    }
}

问题很可能是您没有在清单中定义 QuizActivity。

例如:-

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".QuizActivity">
    </activity>
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

即你需要的

    <activity android:name=".QuizActivity">
    </activity>

将 QuizActivity 定义为可以启动的活动。

此外，我的 SQLite 数据库不会将硬编码的数据插入 它使用 QuizActivity Java 类。

如果仅在 QuizActivity 中访问数据库，则不会，

• 请注意，仅实例化 QuizDBHelper 并不会真正创建数据库，

直到尝试获取可写或可读数据库（这可以通过 SQliteDatabase 方法隐含，或者可以通过使用 getWritableDatabase 或 getReadableDatabase 显式）创建数据库并且硬调用 onCreate 方法然后添加编码问题（它确实添加了它们）。

所以我相信您只需要相应地编辑清单文件 AndroidManifest.xml。

最好在重新运行之前删除应用数据或卸载应用。