无法使用来自Future函数中参数的数据

debugcn 发表于 Dev

塞尔梅德·贝瓦里（Sermed Berwari）

我有页面将数据作为参数发送到其他页面，第二个页面在其中接收参数（Widget build（BuildContext context）），所以Future函数位于页面Class的开头，如下代码：

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';

class Days extends StatefulWidget {
  @override
  _DaysState createState() => _DaysState();
}

class _DaysState extends State<Days> {
  var cm_id;
  var d_id;
  var w_id;
  var u_id;
  Map rdata = {};
  Map data = {};
  List digrees;
  Future getDigrees() async {
    var url = 'http://10.0.2.2/jiyan/test/api/digrees/day_digree.php?u_id=' +
        u_id +
        '&m_id=' +
        cm_id +
        '&d_id=' +
        d_id;
    var response = await http.get(url);
    data = jsonDecode(response.body);
  }
  @override
  void initState() {
    super.initState();
    getDigrees();
  }
  @override
  Widget build(BuildContext context) {
    rdata = ModalRoute.of(context).settings.arguments;
    setState(() {
      cm_id = int.parse(rdata['current_m_id'].toString());
      d_id = int.parse(rdata['d_id'].toString());
      w_id = int.parse(rdata['w_id'].toString());
      u_id = int.parse(rdata['u_id'].toString());
    });
    return Scaffold()

现在，该函数无法接收这些数据，我该怎么办？

尼克拉斯·莱恩菲尔德

您应该考虑不要将所有内容作为成员变量置于状态中。尝试尽可能多地使用依赖项注入（将所需的所有内容用作方法参数）。
在Dart中，使用$这样的字符串连接很容易：

int a = 5;
int b = 10;
String result = "$a + $b = ${a+b}";

这是我建议的代码：

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';

class Days extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return FutureBuilder(
      future: fetchDigrees(context),
      builder: (context, snapshot) {
        if (snapshot.connectionState != ConnectionState.done) {
          return Center(
            child: Text("Loading...."),
          );
        }

        List digrees = snapshot.data;

        return Text(digrees.length.toString());
      },
    );
  }

  Future<List> fetchDigrees(BuildContext context) async {
    Map rdata = ModalRoute.of(context).settings.arguments;

    int cm_id = int.parse(rdata['current_m_id'].toString());
    int d_id = int.parse(rdata['d_id'].toString());
    int w_id = int.parse(rdata['w_id'].toString());
    int u_id = int.parse(rdata['u_id'].toString());

    var url =
        'http://10.0.2.2/jiyan/test/api/digrees/day_digree.php?u_id=$u_id&m_id=$cm_id&d_id=$d_id';
    var response = await http.get(url);
    var data = jsonDecode(response.body);

    return data["digrees"]; //or however you have to extract this from the json
  }
}

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