目前正在关注有关 Android 中集成 SQLite 的测验应用程序的 YouTube 教程。链接在这里:https://www.youtube.com/watch?v=pEDVdSUuWXE
我一直在关注他的最细节，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 将不会启动。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;
}
}
这是用于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？
最佳答案
查询有问题吗？
没有。
您复制和测试的代码没有问题。
使用仅由一个按钮组成的 Activity MainActivity，可以单击该按钮来启动测验 Activity ，并通过问题启动测验 Activity 。
使用后退按钮返回到主 Activity ，然后单击该按钮显示下一个问题。
在我的主要 Activity 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);
}
});
}
}
问题很可能是您尚未在 list 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>
即您需要的
<activity android:name=".QuizActivity">
</activity>
将 QuizActivity 定义为可以启动的 Activity 。
Furthermore, my SQLite database won't insert the data hardcoded into it using the QuizActivity Java class.
如果仅在 QuizActivity 中访问数据库，则不会，
- 请注意，简单地实例化 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 方法隐式实现，也可以通过使用 getWritableDatabase 或 getReadableDatabase 显式实现)，数据库才会被创建，并且 onCreate 方法才会被硬调用。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 list 文件AndroidManifest.xml。
最好在重新运行之前删除应用程序数据或卸载应用程序。
关于java - 使用 SQLite 数据库时我的 Activity 无法打开，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/53546490/