java - 如何在Android SQLite中的现有表上添加列？

如何在现有表登录名中添加列。这是我的示例代码。
这是我的databaseadapter类：

public class DataBaseHelper extends SQLiteOpenHelper
{
    public DataBaseHelper(Context context, String name,CursorFactory factory, int version)
    {
               super(context, name, factory, version);
    }
    // Called when no database exists in disk and the helper class needs
    // to create a new one.
    @Override
    public void onCreate(SQLiteDatabase _db)
    {
            _db.execSQL(LoginDataBaseAdapter.DATABASE_CREATE);

    }
    // Called when there is a database version mismatch meaning that the version
    // of the database on disk needs to be upgraded to the current version.
    @Override
    public void onUpgrade(SQLiteDatabase _db, int _oldVersion, int _newVersion)
    {
            // Log the version upgrade.
            Log.w("TaskDBAdapter", "Upgrading from version " +_oldVersion + " to " +_newVersion + ", which will destroy all old data");


            // Upgrade the existing database to conform to the new version. Multiple
            // previous versions can be handled by comparing _oldVersion and _newVersion
            // values.
            // The simplest case is to drop the old table and create a new one.
            _db.execSQL("DROP TABLE IF EXISTS " + "TEMPLATE");
            // Create a new one.
            onCreate(_db);
    }

这是我的登录数据库适配器

public class LoginDataBaseAdapter
{
        static final String DATABASE_NAME = "login.db";
        static final int DATABASE_VERSION = 1;
        public static final int NAME_COLUMN = 1;
        // TODO: Create public field for each column in your table.
        // SQL Statement to create a new database.
        static final String DATABASE_CREATE = "create table "+"LOGIN"+
                                     "( " +"ID"+" integer primary key autoincrement,"+ "USERNAME  text,PASSWORD text); ";
        // Variable to hold the database instance
        public  SQLiteDatabase db;
        // Context of the application using the database.
        private final Context context;
        // Database open/upgrade helper
        private DataBaseHelper dbHelper;
        public  LoginDataBaseAdapter(Context _context)
        {
            context = _context;
            dbHelper = new DataBaseHelper(context, DATABASE_NAME, null, DATABASE_VERSION);
        }
        public  LoginDataBaseAdapter open() throws SQLException
        {
            db = dbHelper.getWritableDatabase();
            return this;
        }
        public void close()
        {
            db.close();
        }

        public  SQLiteDatabase getDatabaseInstance()
        {
            return db;
        }

        public void insertEntry(String userName,String password)
        {
           ContentValues newValues = new ContentValues();
            // Assign values for each row.
            newValues.put("USERNAME", userName);
            newValues.put("PASSWORD",password);

            // Insert the row into your table
            db.insert("LOGIN", null, newValues);
            ///Toast.makeText(context, "Reminder Is Successfully Saved", Toast.LENGTH_LONG).show();
        }
        public int deleteEntry(String UserName)
        {
            //String id=String.valueOf(ID);
            String where="USERNAME=?";
            int numberOFEntriesDeleted= db.delete("LOGIN", where, new String[]{UserName}) ;
           // Toast.makeText(context, "Number fo Entry Deleted Successfully : "+numberOFEntriesDeleted, Toast.LENGTH_LONG).show();
            return numberOFEntriesDeleted;
        }
        public String getSinlgeEntry(String userName1)
        {
            Cursor cursor=db.query("LOGIN", null, " USERNAME=?", new String[]{userName1}, null, null, null);
            if(cursor.getCount()<1) // UserName Not Exist
            {
                cursor.close();
                return "NOT EXIST";
            }
            cursor.moveToFirst();
            String password= cursor.getString(cursor.getColumnIndex("PASSWORD"));
            cursor.close();
            return password;
        }
        public void  updateEntry(String userName,String password)
        {
            // Define the updated row content.
            ContentValues updatedValues = new ContentValues();
            // Assign values for each row.
            updatedValues.put("USERNAME", userName);
            updatedValues.put("PASSWORD",password);

            String where="USERNAME = ?";
            db.update("LOGIN",updatedValues, where, new String[]{userName});
        }
}

如何添加列firstname（来自textview）、lastname（来自textview）、department（来自spinner）。

最佳答案

首先必须更新sqlite数据库版本，然后运行onupgrade（）方法，该方法将删除所有数据。然后将使用数据库创建字符串中定义的新架构重新生成表。
因此，随之而来的主要问题是，在删除表时，必须找到恢复表中已存在的数据的方法。不过，在这种情况发生之前，您确实需要运行onupgrade，因此请使用此方法作为一个点来保存您需要从数据库中保存的任何数据。

static final int DATABASE_VERSION = 2;

并更新数据库创建字符串。

关于java - 如何在Android SQLite中的现有表上添加列？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/17984367/