所以我正在创建一个琐事游戏，我的问题是尝试向数据库添加问题。我认为如果整个表被删除并不重要但我似乎无法让它工作。我查看了无数的帖子，无法弄清楚我做错了什么。我的数据库已设置好，因此每个类别都是自己的表。
package com.triviagame;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.sql.SQLException;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class DataBaseHelper extends SQLiteOpenHelper{
//The Android's default system path of the application's database.
private static String DB_PATH = "/data/data/com.triviagame/databases/";
private static String DB_NAME = "mobile_trivia2.db";
private SQLiteDatabase myDataBase;
private final Context myContext;
private static final String DATABASE_TABLE = "geography";
private static final int DATABASE_VERSION = 3;
/* Constructor
* Takes and keeps a reference of the passed context in order to access to the application assets and resources.
* @param context
*/
public DataBaseHelper(Context context) {
super(context, DB_NAME, null, DATABASE_VERSION);
this.myContext = context;
}
/**
* Creates a empty database on the system and rewrites it with your own database.
* */
public void createDataBase() throws IOException{
boolean dbExist = checkDataBase();
if(dbExist){
//do nothing - database already exist
}
else{
//By calling this method and empty database will be created into the default system path
//of your application so we are going to be able to overwrite that database with our database.
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
/**
* Check if the database already exist to avoid re-copying the file each time you open the application.
* @return true if it exists, false if it doesn't
*/
private boolean checkDataBase(){
SQLiteDatabase checkDB = null;
try{
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}catch(SQLiteException e){
//database does't exist yet.
Log.e("DBHelper", "DataBase Does Not Exist closing returning null");
}
if(checkDB != null){
Log.e("DBHelper", "DataBase Exists closing checkDB");
checkDB.close();
}
return checkDB != null ? true : false;
}
/**
* Copies your database from your local assets-folder to the just created empty database in the
* system folder, from where it can be accessed and handled.
* This is done by transferring byte-stream.
* */
private void copyDataBase() throws IOException{
//Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DB_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DB_NAME;
//Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(outFileName);
//transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer))>0){
myOutput.write(buffer, 0, length);
}
//Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
}
public void openDataBase() throws SQLException{
//Open the database
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
@Override
public synchronized void close() {
if(myDataBase != null)
myDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
}
//Returns the question from the database using the category ID and the question ID passed to it
public String getQuestion( int categoryId, int questionId){
final String[] FROM = {"question"}; //string array of which columns to look through in the table
String categoryStr = "General"; //default value
//converts the numeric category ID to its corresponding String value
switch (categoryId){
case 0:
categoryStr = "geography"; break;
case 1:
categoryStr = "politics"; break;
case 2:
categoryStr = "History"; break;
case 3:
categoryStr = "sports"; break;
case 4:
categoryStr = "science"; break;
case 5:
categoryStr = "movies"; break;
case 6:
categoryStr = "General"; break;
default:
categoryStr = "General"; break;
}
Cursor cursor = myDataBase.query(categoryStr, FROM, "_id=="+questionId, null, null, null, null);//build the query, pass null for default filtering
cursor.moveToFirst();//move the cursor to the first index location in the result column
String result=cursor.getString(0);//return the first result column (index 0)
return result; //returns question
}
//Returns the correct answer according the the category ID and the question ID passed to it
public String getCorrectAnswer( int categoryId, int questionId){
final String[] FROM = {"correct"}; //string array of which columns to look through in the table
String categoryStr = "General"; //Default value
//converts the numeric category ID to its corresponding String value
switch (categoryId){
case 0:
categoryStr = "geography"; break;
case 1:
categoryStr = "politics"; break;
case 2:
categoryStr = "History"; break;
case 3:
categoryStr = "sports"; break;
case 4:
categoryStr = "science"; break;
case 5:
categoryStr = "movies"; break;
case 6:
categoryStr = "General"; break;
default:
categoryStr = "General";
}
Cursor cursor=myDataBase.query(categoryStr, FROM, "_id=="+questionId, null, null, null, null);//build the query, pass null for default filtering
cursor.moveToFirst();//move the cursor to the first index location in the result column
String result=cursor.getString(0);//return the first result column (index 0)
return result; //returns correct answer
}
//Returns the first wrong answer from the database according to the category ID and question ID passed to it
public String getWrongAnswer1( int categoryId, int questionId){
final String[] FROM = {"wrong1"}; //string array of which columns to look through in the table
String categoryStr = "General"; //default value
//converts the numeric category ID to its corresponding String value
switch (categoryId){
case 0:
categoryStr = "geography"; break;
case 1:
categoryStr = "politics"; break;
case 2:
categoryStr = "History"; break;
case 3:
categoryStr = "sports"; break;
case 4:
categoryStr = "science"; break;
case 5:
categoryStr = "movies"; break;
case 6:
categoryStr = "General"; break;
default:
categoryStr = "General";
}
Cursor cursor=myDataBase.query(categoryStr, FROM, "_id=="+questionId, null, null, null, null);//build the query, pass null for default filtering
cursor.moveToFirst();//move the cursor to the first index location in the result column
String result=cursor.getString(0);//return the first result column (index 0)
return result; //returns first wrong answer
}
//Returns the second wrong answer from the database according to the category ID and question ID passed to it
public String getWrongAnswer2( int categoryId, int questionId){
final String[] FROM = {"wrong2"}; //string array of which columns to look through in the table
String categoryStr = "General"; //default value
//converts the numeric category ID to its corresponding String value
switch (categoryId){
case 0:
categoryStr = "geography"; break;
case 1:
categoryStr = "politics"; break;
case 2:
categoryStr = "History"; break;
case 3:
categoryStr = "sports"; break;
case 4:
categoryStr = "science"; break;
case 5:
categoryStr = "movies"; break;
case 6:
categoryStr = "General"; break;
default:
categoryStr = "General";
}
Cursor cursor=myDataBase.query(categoryStr, FROM, "_id=="+questionId, null, null, null, null);//build the query, pass null for default filtering
cursor.moveToFirst();//move the cursor to the first index location in the result column
String result=cursor.getString(0);//return the first result column (index 0)
return result; //returns second wrong answer
}
//Returns the second wrong answer from the database according to the category ID and question ID passed to it
public String getWrongAnswer3( int categoryId, int questionId){
final String[] FROM = {"wrong3"}; //string array of which columns to look through in the table
String categoryStr = "General";
//converts the numeric category ID to its corresponding String value
switch (categoryId){
case 0:
categoryStr = "geography"; break;
case 1:
categoryStr = "politics"; break;
case 2:
categoryStr = "History"; break;
case 3:
categoryStr = "sports"; break;
case 4:
categoryStr = "science"; break;
case 5:
categoryStr = "movies"; break;
case 6:
categoryStr = "General"; break;
default:
categoryStr = "General";
}
Cursor cursor=myDataBase.query(categoryStr, FROM, "_id==" + questionId, null, null, null, null);//build the query, pass null for default filtering
cursor.moveToFirst();//move the cursor to the first index location in the result column
String result=cursor.getString(0);//return the first result column (index 0)
return result; //returns third wrong answer
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
if (oldVersion < 2) {
db.execSQL("DROP TABLE IF EXISTS "+DATABASE_TABLE);
onCreate(db);
}
}
}
答案 0 :(得分：4)
当现有数据库版本小于您在
中传递的版本时，始终会调用onUpgrade方法super(context, DB_NAME, null, DATABASE_VERSION);
您将3作为数据库版本传递。我假设您的旧版本是2，但您明确地希望升级仅适用于数据库OLDER而不是2.只需从onUpgrade中删除IF。
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS "+DATABASE_TABLE);
onCreate(db);
}