我正在进行测验申请。我已经完成了一个预填充的数据库,其中包括questionNumber,主题,问题,correctAnswer,错Answer1,错Answer2和错Answer3作为其列(查看底部的图片)。我正在测试查询数据库是否可以工作,因此我创建了一个名为TestActivity的类及其相应的XML文件“ activity_test”。我包括一个按钮和一个textView。我的目标是查询数据库,并在单击按钮时在textView中显示它。我的问题是,在随SQLiteOpenHelper扩展的DatabaseHelper类中,创建了一个空数据库,而不是查询预先填充的数据库。我不知道我在哪里做错了,但是我高度怀疑这是CREATE_TABLE的错。我可能打错了字。我尝试重新键入和重新键入模式,但在textView中仍然没有显示记录。
在此测试中,我仅尝试查询“ wrongAnswers3”列,因为数据库有太多记录。
这是我的“ DatabaseAdapter”类
package com.example.quizalarm;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DatabaseAdapter {
static class DatabaseHelper extends SQLiteOpenHelper {
private static final String DATABASE_NAME="qasadb.db";
private static final String TABLE_NAME="qasaMultipleChoicequizdb";
private static final String QUESTION_NUMBER="questionNumber";
private static final String SUBJECT="subject";
private static final String QUESTION="question";
private static final String CORRECT_ANSWER="correctAnswer";
private static final String WRONG_ANSWER1="wrongAnswer1";
private static final String WRONG_ANSWER2="wrongAnswer2";
private static final String WRONG_ANSWER3="wrongAnswer3";
private static final String CREATE_TABLE="CREATE TABLE "+
TABLE_NAME+" ( "+
QUESTION_NUMBER+" INTEGER PRIMARY KEY AUTOINCREMENT, "+
SUBJECT+" TEXT, "+
QUESTION+" TEXT, "+
CORRECT_ANSWER+" TEXT, "+
WRONG_ANSWER1+" TEXT, " +
WRONG_ANSWER2+" TEXT, "+
WRONG_ANSWER3+" TEXT" +
")";
private static final String DROP_TABLE="DROP TABLE IF EXISTS "+TABLE_NAME;
private static final int DATABASE_VERSION=1;
private Context context;
//constructor
public DatabaseHelper(Context context){
super(context, DATABASE_NAME, null, DATABASE_VERSION);
this.context = context;
Message.message(context, "Constructor called");
}
@Override
public void onCreate(SQLiteDatabase db) {
try {
db.execSQL(CREATE_TABLE);
Message.message(context, "onCreate was called");
} catch (SQLException e){
Message.message(context, ""+e);
}
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
try {
Message.message(context, "onUpgrade was called");
db.execSQL(DROP_TABLE);
onCreate(db);
} catch (SQLException e){
e.printStackTrace();
}
}
}
DatabaseHelper helper;
public DatabaseAdapter (Context context){
helper = new DatabaseHelper(context);
}
public String getData(){
SQLiteDatabase db=helper.getWritableDatabase();
//select necessary columns from table
String[] columns={DatabaseHelper.WRONG_ANSWER3};
Cursor cursor=db.query(DatabaseHelper.TABLE_NAME, columns, null, null, null, null, null);
StringBuffer sb=new StringBuffer();
while (cursor.moveToNext()){
String cWA3 = cursor.getString(6);
sb.append(cWA3);
}
return sb.toString();
}
}
这是我的“ TestActivity”类
package com.example.quizalarm;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;
import androidx.appcompat.app.AppCompatActivity;
public class TestActivity extends AppCompatActivity {
DatabaseAdapter helper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_test);
helper = new DatabaseAdapter(this);
}
public void viewDetails(View view){
TextView textShowData = findViewById(R.id.textShowData);
String data = helper.getData();
textShowData.setText(data);
}
}
其“ qasaMultipleChoicequizdb”表的架构是创建表“ qasaMultipleChoicequizdb”(“ questionNumber”整数主键自动递增,“主题” TEXT,“问题” TEXT,“ correctAnswer” TEXT,“ wrongAnswer1” TEXT,“ wrongAnswer2” TEXT,“ wrongAnswer3” TEXT)
我对此代码的引用来自this playlist。零件/视频160-166)。
对我来说,使用SQLiteAssetHelper比使用SQLiteOpenHelper容易得多。您无需使用“ CREATE TABLE”架构,只需在build.gradle(模块:app)中添加特定的依赖项即可使用此功能。
这里是链接:https://www.javahelps.com/2015/04/import-and-use-external-database-in.html。
希望有帮助:)