如何在Flutter中使用下拉列表中的API？

Question

工作条件下的输出 Flutter/Dart 程序员您好，我是 Flutter 新手。下面关于下拉列表的代码可以在没有 API 的情况下工作，但我希望 API 数据显示在下拉列表中......我需要帮助

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

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter DropDownButton',
      theme: ThemeData(
        primarySwatch: Colors.green,
      ),
      home: const MyHomePage(),
      debugShowCheckedModeBanner: false,
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  String selectValue = "";
  List categoryItemlist = [];

  //List categoryItemlist = List();  //it is not working

  // ***********************************************************
  // Fetch data from JSON/API File
  Future getAllCategory() async {
    var baseUrl = "https://gssskhokhar.com/api/classes/";

    http.Response response = await http.get(Uri.parse(baseUrl));

    if (response.statusCode == 200) {
      var jsonData = json.decode(response.body);
      setState(() {
        categoryItemlist = jsonData;
      });
    }
    print(categoryItemlist);
  }

  @override
  void initState() {
    super.initState();
    getAllCategory();
  }
  // ***********************************************************

// Initial Selected Value
  String dropdownvalue = 'Item 1';

// List of items in our dropdown menu
  var items = [
    'Item 1',
    'Item 2',
    'Item 3',
    'Item 4',
    'Item 5',
  ];
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text("DropDown List"),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            DropdownButton(
              // Initial Value
              value: dropdownvalue,

              // Down Arrow Icon
              icon: const Icon(Icons.keyboard_arrow_down),

              // Array list of items
              items: items.map((String items) {
                return DropdownMenuItem(
                  value: items,
                  child: Text(items),
                );
              }).toList(),
              // After selecting the desired option,it will
              // change button value to selected value
              onChanged: (String? newValue) {
                setState(() {
                  dropdownvalue = newValue!;
                });
              },
            ),
          ],
        ),
      ),
    );
  }
}

输出图片附有工作条件，但没有 API/JSON。但我希望 API 数据显示在下拉列表中......

Answer 1

用于FutureBuilder构建需要Future价值的小部件。

DropDownMenuIems您可以从方法中返回新列表，getAllCategory()而不是更新旧项目。喜欢：

Future<List<String>> getAllCategory() async {
    var baseUrl = "https://gssskhokhar.com/api/classes/";

    http.Response response = await http.get(Uri.parse(baseUrl));

    if (response.statusCode == 200) {
      List<String> items = [];
      var jsonData = json.decode(response.body) as List;
      for (var element in jsonData) {
        items.add(element["ClassName"]);
      }
      return items;
    } else {
      //Handle Errors
      throw response.statusCode;
    }
  }

然后你可以getAllCategory()作为 的未来给予FutureBuilder。FutureBuilder将根据提供的构建不同的小部件Future。你可以返回，CircularProgressIndicator直到未来没有价值。获得您的后，DropDownMenuItems您可以归还您的DropDownMenu。喜欢：

           FutureBuilder<List<String>>(
              future: getAllCategory(),
              builder: (context, snapshot) {
                if (snapshot.hasData) {
                  var data = snapshot.data!;
                  return DropdownButton(
                    // Initial Value
                    value: dropdownvalue ?? data[0],

                    // Down Arrow Icon
                    icon: const Icon(Icons.keyboard_arrow_down),

                    // Array list of items
                    items: data.map((String items) {
                      return DropdownMenuItem(
                        value: items,
                        child: Text(items),
                      );
                    }).toList(),
                    // After selecting the desired option,it will
                    // change button value to selected value
                    onChanged: (String? newValue) {
                      setState(() {
                        dropdownvalue = newValue!;
                      });
                    },
                  );
                } else {
                  return const CircularProgressIndicator();
                }
              },
            )

完整代码：

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

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter DropDownButton',
      theme: ThemeData(
        primarySwatch: Colors.green,
      ),
      home: const MyHomePage(),
      debugShowCheckedModeBanner: false,
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  String? dropdownvalue;

  Future<List<String>> getAllCategory() async {
    var baseUrl = "https://gssskhokhar.com/api/classes/";

    http.Response response = await http.get(Uri.parse(baseUrl));

    if (response.statusCode == 200) {
      List<String> items = [];
      var jsonData = json.decode(response.body) as List;
      for (var element in jsonData) {
        items.add(element["ClassName"]);
      }
      return items;
    } else {
      throw response.statusCode;
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text("DropDown List"),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            FutureBuilder<List<String>>(
              future: getAllCategory(),
              builder: (context, snapshot) {
                if (snapshot.hasData) {
                  var data = snapshot.data!;
                  return DropdownButton(
                    // Initial Value
                    value: dropdownvalue ?? data[0],

                    // Down Arrow Icon
                    icon: const Icon(Icons.keyboard_arrow_down),

                    // Array list of items
                    items: data.map((String items) {
                      return DropdownMenuItem(
                        value: items,
                        child: Text(items),
                      );
                    }).toList(),
                    // After selecting the desired option,it will
                    // change button value to selected value
                    onChanged: (String? newValue) {
                      setState(() {
                        dropdownvalue = newValue!;
                      });
                    },
                  );
                } else {
                  return const CircularProgressIndicator();
                }
              },
            ),
          ],
        ),
      ),
    );
  }
}