我有一个问题,我已经解决但我仍然想知道为什么
解决方案解决了它.
我编写了一个 Android应用程序,在我调试它几次后有一个sqlite数据库
db中的oncreate方法没有被调用(即使之前一切正常)
我将db版本号从1更改为2后,一切正常
即使我通过应用程序管理器卸载了应用程序,也删除了缓存
本地数据库信息.
我的问题如下 – 本地数据库数据是否保存在其他地方？
如果没有 – 为什么它只在我升级版本号后才有效
甚至当我删除所有与应用相关的数据时？

/**
 * A class to handle sqlite reads/writes of user related data to be collected
 */
public class UserDataManager extends sqliteOpenHelper {

    // Class Variables
    private final String TAG = UserDataManager.class.getSimpleName();

    // Database Version
    private static final int DATABASE_VERSION = 1;

    // Database Name
    public static final String DATABASE_NAME = "tmc";

    // Tables
    private static final String TABLE_USER = "user";

    // Tables and table columns names
    private String CREATE_USER_TABLE;
    private static final String COLUMN_USER_ID = "user_id";
    private static final String COLUMN_USER_MAIL = "email";
    private static final String COLUMN_USER_ACTIVE = "user_active";
    private static final String COLUMN_USER_NAME = "name";
    private static final String COLUMN_USER_PASSWORD = "password";
    private static final String COLUMN_USER_PHONE_NUMBER = "phone_number";

    /**
     * Class constructor
     * 
     * @param context
     *            The context to run in
     */
    public UserDataManager(Context context) {
        super(context,DATABASE_NAME,null,DATABASE_VERSION);
    }

    // Creating Tables
    @Override
    public void onCreate(sqliteDatabase db) {

        CREATE_USER_TABLE = "CREATE TABLE IF NOT EXISTS " + TABLE_USER + " ("
                + COLUMN_USER_ID + " INTEGER PRIMARY KEY NOT NULL,"
                + COLUMN_USER_MAIL + " VARCHAR(64) NOT NULL,"
                + COLUMN_USER_NAME + " VARCHAR(64) NOT NULL,"
                + COLUMN_USER_PASSWORD + " VARCHAR(64) NOT NULL,"
                + COLUMN_USER_PHONE_NUMBER + " VARCHAR(64) NOT NULL,"
                + COLUMN_USER_ACTIVE + " INT NOT NULL);";

        // create the tables
        db.execsql(CREATE_USER_TABLE);
    }

    // Upgrading database
    @Override
    public void onUpgrade(sqliteDatabase db,int oldVersion,int newVersion) {

        // Drop older table if existed
        db.execsql("DROP TABLE IF EXISTS " + TABLE_USER);

        // Create tables again
        onCreate(db);
    }

    /**
     * Adding a user to the database
     * 
     * @param userId
     *            The created user id
     * @param userName
     *            The user name
     * @param userEmail
     *            The user email
     * @param userPassword
     *            The user password
     * @param userPhoneNumber
     *            The user phone number
     * @param isActive
     *            Set to 1 if the user is active 0 otherwise
     * @return True if the user added successfully false otherwise
     */
    public boolean AddUser(int userId,String userName,String userEmail,String userPassword,String userPhoneNumber,boolean isActive) {

        // method variables
        long rowId;
        boolean pass = false;
        int active = isActive ? 1 : 0;
        sqliteDatabase db = null;
        ContentValues row = null;

        // try to add the user to the db
        try {
            row = new ContentValues();
            db = this.getWritableDatabase();
            db.delete(TABLE_USER,null);
            row.put(COLUMN_USER_ID,userId);
            row.put(COLUMN_USER_NAME,userName);
            row.put(COLUMN_USER_MAIL,userEmail);
            row.put(COLUMN_USER_PASSWORD,userPassword);
            row.put(COLUMN_USER_CAR_NUMBER,userPhoneNumber);
            row.put(COLUMN_USER_ACTIVE,active);
            rowId = db.insert(TABLE_USER,row);
            if (rowId > -1) {
                pass = true;
            }
        } catch (sqlException exception) {
            Log.e(TAG,exception.getMessage());
        } finally {
            if (db != null) {
                // close database connection
                db.close();
            }
        }
        return pass;
    }

    /**
     * Get the current registered user
     * 
     * @return The id of the column of the registered user
     */
    public int GetRegisteredUserId() {

        // method variables
        int columnIndex = -1;
        int userId = -1;
        sqliteDatabase db = null;
        Cursor cursor = null;

        // try to get the user from the database
        try {
            db = this.getReadableDatabase();
            cursor = db.query(TABLE_USER,new String[] { COLUMN_USER_ID },null);
            if (cursor != null) {
                boolean moved = cursor.moveToFirst();
                if (moved) {
                    columnIndex = cursor.getColumnIndex(COLUMN_USER_ID);
                    if (columnIndex > -1) {
                        userId = cursor.getInt(columnIndex);
                    }
                }
            }
        } catch (sqlException exception) {
            Log.e(TAG,exception.getMessage());
        } finally {
            if (cursor != null)
                // release cursor
                cursor.close();
            if (db != null)
                // close database connection
                db.close();
        }
        return userId;
    }

    /**
     * Get the current user email
     * 
     * @return The id of the column of the registered user
     */
    public String GetRegisteredUserEmail() {

        // method variables
        int columnIndex = -1;
        String userEmail = null;
        sqliteDatabase db = null;
        Cursor cursor = null;

        // try to get the user from the database
        try {
            db = this.getReadableDatabase();
            cursor = db.query(TABLE_USER,new String[] { COLUMN_USER_MAIL },null);
            if (cursor != null) {
                boolean moved = cursor.moveToFirst();
                if (moved) {
                    columnIndex = cursor.getColumnIndex(COLUMN_USER_MAIL);
                    if (columnIndex > -1) {
                        userEmail = cursor.getString(columnIndex);
                    }
                }
            }
        } catch (sqlException exception) {
            Log.e(TAG,exception.getMessage());
        } finally {
            if (cursor != null)
                // release cursor
                cursor.close();
            if (db != null)
                // close database connection
                db.close();
        }
        return userEmail;
    }

    /**
     * Get the current user password
     * 
     * @return The password of the current logged user
     */
    public String GetRegisteredUserPassword() {

        // method variables
        int columnIndex = -1;
        String userPassword = null;
        sqliteDatabase db = null;
        Cursor cursor = null;

        // try to get the user from the database
        try {
            db = this.getReadableDatabase();
            cursor = db.query(TABLE_USER,new String[] { COLUMN_USER_PASSWORD },null);
            if (cursor != null) {
                boolean moved = cursor.moveToFirst();
                if (moved) {
                    columnIndex = cursor.getColumnIndex(COLUMN_USER_PASSWORD);
                    if (columnIndex > -1) {
                        userPassword = cursor.getString(columnIndex);
                    }
                }
            }
        } catch (sqlException exception) {
            Log.e(TAG,exception.getMessage());
        } finally {
            if (cursor != null)
                // release cursor
                cursor.close();
            if (db != null)
                // close database connection
                db.close();
        }
        return userPassword;
    }

    /**
     * Get number of rows in the user table
     * 
     * @return the number of the rows in the user table (How many users are
     *         saved in the DB)
     */
    public int GetRowCount() {

        // method variables
        int rowsCount = 0;
        sqliteDatabase db = null;
        Cursor cursor = null;

        // try to get the user from the database
        try {
            db = this.getReadableDatabase();
            cursor = db.query(TABLE_USER,null);
            if (cursor != null) {
                boolean moved = cursor.moveToFirst();
                if (moved) {
                    do {
                        rowsCount++;
                    } while (cursor.moveToNext());
                }
            }
        } catch (sqlException exception) {
            Log.e(TAG,exception.getMessage());
        } finally {
            if (cursor != null)
                // release cursor
                cursor.close();
            if (db != null)
                // close database connection
                db.close();
        }
        return rowsCount;
    }

    /**
     * Remove a user from the database
     * 
     * @param userId
     *            The user id
     */
    public void logoutUser() {

        // method variables
        sqliteDatabase db = null;

        // try to remove a user from the database
        try {
            db = this.getWritableDatabase();
            onUpgrade(db,DATABASE_VERSION,DATABASE_VERSION);
        } catch (sqlException exception) {
            Log.e(TAG,exception.getMessage());
        } finally {
            if (db != null) {
                // close database connection
                db.close();
            }
        }
    }

    /**
     * Set a user to be active or not
     * 
     * @param isActive
     *            1 if the cigarette is active 0 otherwise
     * @return True if the cigarette active field has changed false otherwise
     */
    public boolean SetUserActive(boolean isActive) {
        // method variables
        int rowsAffected;
        int active = isActive ? 1 : 0;
        long userId;
        String userIdString;
        boolean pass = true;
        sqliteDatabase db = null;
        ContentValues values = null;

        // try to remove a device from the database
        try {
            userId = GetRegisteredUserId();
            if (userId > -1) {
                userIdString = String.valueOf(userId);
                db = this.getWritableDatabase();
                values = new ContentValues();
                values.put(COLUMN_USER_ACTIVE,active);
                rowsAffected = db.update(TABLE_USER,values,COLUMN_USER_ID
                        + " = ?",new String[] { userIdString });
                if (rowsAffected != 1) {
                    pass = false;
                }
            }
        } catch (sqlException exception) {
            Log.e(TAG,exception.getMessage());
        } finally {
            if (db != null) {
                // close database connection
                db.close();
            }
        }
        return pass;
    }
}

笔记 –
1.请注意我的设备已植根,所以在将数据插入数据库后我将更改数据库的777权限,以便我可以从手机中取出它以查看其中的内容(即查询是否通过)
2.抛出的错误是“android.database.sqlite.sqliteException：no such table：user”

巧克力饼干将被授予任何答案… =)

try {
       File sd = Environment.getExternalStorageDirectory();
       File data = Environment.getDataDirectory();
        if (sd.canWrite()) {
        String currentDBPath = "/data/data/" + getPackageName() + "/databases/ZnameDB"; //Your DATABASE_NAME
        String backupDBPath = "ZnameDB_Dev.db"; //DATABASE_COPY_NAME UNDER SDCARD
        File currentDB = new File(currentDBPath);
        File backupDB = new File(sd,backupDBPath);
        if (currentDB.exists()) {
        FileChannel src = new FileInputStream(currentDB).getChannel();
        FileChannel dst = new FileOutputStream(backupDB).getChannel();
        dst.transferFrom(src,src.size());
        src.close();
        dst.close();
        Toast.makeText(SettingsActivity.this,"Database Transfered!",Toast.LENGTH_SHORT).show();
          }
         }
     } catch (Exception e) {
        Log.e(TAG,e.toString());
    }