Question

给出一个类，如何从字段字典中创建它的实例？这是一个示例来说明我的问题：

from typing import Tuple, Mapping, Any


def new_instance(of: type, with_fields: Mapping[str, Any]):
    """How to implement this?"""
    return ...


class A:
    """Example class"""

    def __init__(self, pair: Tuple[int, int]):
        self.first = pair[0]
        self.second = pair[1]

    def sum(self):
        return self.first + self.second


# Example use of new_instance
a_instance = new_instance(
    of=A,
    with_fields={'first': 1, 'second': 2}
)

Answer 1

请参见How to create a class instance without calling initializer?绕过初始化程序。然后从字典中设置属性。

import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'home_page.dart';
import 'auth.dart';
import 'login_page.dart';

void main() => runApp(
  ChangeNotifierProvider<AuthService>(
    child: MyApp(),
    builder: (BuildContext context) {
      return AuthService();
    },
  ),
);

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(primarySwatch: Colors.blue),
      home: FutureBuilder<FirebaseUser>(
        future: Provider.of<AuthService>(context).getUser(),
        builder: (context, AsyncSnapshot<FirebaseUser> snapshot) {
          if (snapshot.connectionState == ConnectionState.done) {
            // log error to console
            if (snapshot.error != null) {
              print("error");
              return Text(snapshot.error.toString());
            }

            // redirect to the proper page
            return snapshot.hasData ? HomePage(snapshot.data) : LoginPage();
          } else {
            // show loading indicator
            return LoadingCircle();
          }
        },
      ),
    );
  }
}

class LoadingCircle extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Center(
      child: Container(
        child: CircularProgressIndicator(),
        alignment: Alignment(0.0, 0.0),
      ),
    );
  }

如何从字典实例化一个类

1 个答案: