android sqlite onUpgrade 不工作

Question

所以我正在创建一个问答游戏，我的问题是尝试将问题添加到数据库中。我认为是否删除整个表并不重要，但我似乎无法让它工作。我查看了无数帖子，无法弄清楚我做错了什么。我的数据库已设置为每个类别都有自己的表格。

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);
        }       
    }  
}

Answer 1

当现有数据库版本低于您传入的版本时，始终调用 onUpgrade 方法

super(context, DB_NAME, null, DATABASE_VERSION);

您传递 3 作为数据库版本。我假设您的旧版本是 2，但您明确希望升级仅适用于早于 2 的数据库。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);

}