5.14

public class UserDao {
    private SQLiteOpenHelper helper;

    public UserDao(Context context) {
        helper = new SQLiteOpenHelper(context, "userser", null, 1);
    }

    //添加数据
    public long addUser(User user) {
        //1.获取数据库对象
        SQLiteDatabase database = helper.getWritableDatabase();
        //那些列为空，可以设置为空
        ContentValues values = new ContentValues();
        //key是数据表的列名，value是要放进去的值
        values.put("username", user.getUsername());
        values.put("password", user.getPassword());
        values.put("age", user.getAge());
        //第一个参数表明，第二个参数自动赋值为null的列名，第三个参数数据
        //返回值long,插入成功行号，插入失败-1
        long i = database.insert("users", null, values);
        //关闭数据库
        database.close();
        return i;
    }

    //删除
    public int deleteUser(String username) {
        //1.获取数据库对象
        SQLiteDatabase database = helper.getWritableDatabase();
        //第一个参数表明，第二个参数为删除条件，第三个参数为第二个参数中占位符所需值组成的字符串数组
        int i = database.delete("users", "username=?", new String[]{username + ""});
        //关闭数据库
        database.close();
        return i;
    }

    //修改
    public int updateUser(User user) {
        //1.获取数据库对象
        SQLiteDatabase database = helper.getWritableDatabase();
        //那些列为空，可以设置为空
        ContentValues values = new ContentValues();
        //key是数据表的列名，value是要放进去的值
        values.put("username", user.getUsername());
        values.put("password", user.getPassword());
        values.put("age", user.getAge());
        //第一个参数表明，第二个参数新数据，第三个参数是条件
        int i = database.update("users", values, "username=?", new String[]{user.getUsername()});
        //关闭数据库
        database.close();
        return i;
    }

    //查询
    public ArrayList queryAll() {
        ArrayList list = new ArrayList();
        SQLiteDatabase database = helper.getWritableDatabase();
        Cursor cursor = database.query("users", null, null, null, null, null, null);
        list = convertFromCursor(cursor);
        return list;
    }

    //通过对Cursor对象遍历查询结果，并将其范围为一个list集合
    private ArrayList convertFromCursor(Cursor cursor) {
        ArrayList list = new ArrayList();
        if (cursor != null && cursor.moveToFirst()) {
            //通过游标遍历这个集合
            do {
                @SuppressLint("Range") int id = cursor.getInt(cursor.getColumnIndex("id"));
                @SuppressLint("Range") String username = cursor.getString(cursor.getColumnIndex("username"));
                @SuppressLint("Range") String password = cursor.getString(cursor.getColumnIndex("password"));
                @SuppressLint("Range") int age = cursor.getInt(cursor.getColumnIndex("age"));
                User user = new User(id, username, password, age);
                list.add(user);
            } while (cursor.moveToNext());
        }
        return list;
    }
}