flutter下拉按钮选择问题

Question

大家好，我刚刚开始flutter，我正在一个小项目中单击dropdownbutton，整个按钮同时更改，以及如何将下拉餐点放在右边？ （检查GIF）

，我想让文本在单元格内部更可读，这是代码，并且要预先感谢。

   import 'package:flutter/material.dart';

class Check_lists extends StatefulWidget {
  String sug_one;
  String sug_two;
  Check_lists(this.sug_one, this.sug_two);

  @override
  State<Check_lists> createState() => _Check_listsState();
}

class _Check_listsState extends State<Check_lists> {
  String dropdownValue = "Not Done";
  int index = 0;
  List<String> propositions = <String>[
    "Single line spacing",
    "Title set below the 2 top margin",
    "Title not exceeding 15 words (including articles,prepositions and conjunctions)",
    "Title in uppercase",
    "Title arranged in an inverted pyramid",
    "All parts centered, and in boldface",
    "4 line skips (5 enter presses) between parts",
    "First name, middle initial(s), last name format for the author’s names",
    "Leader's name followed by members names",
    "alphabetized by surname",
    "Date of proposal stated as month, day, year",
    "Start of pagination"
  ];
  //List<String> answer = ["Done", "partially Done", "Not Done"];
  List<String> selectedItemValue = <String>[];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          backgroundColor: const Color.fromRGBO(82, 113, 255, 25),
          title: Row(
            children: [
              Container(
                  padding: const EdgeInsets.all(10.0),
                  child: const Text('CHEKILI Table of Content'))
            ],
          ),
        ),
        body: Column(
          children: <Widget>[
            Flexible(
              child: ListView.builder(
                itemCount: propositions.length,
                itemExtent: 50.0,
                itemBuilder: (BuildContext context, int index) {
                  for (int i = 0; i < propositions.length; i++) {
                    selectedItemValue.add("Not Done");
                  }
                  return ListTile(
                    title: Text("${propositions[index]}"),
                    leading: _dropdown(),
                  );
                },
              ),
            ),
          ],
        ));
  }

  Widget _dropdown() {
    return DropdownButton<String>(
      isExpanded: false,
      value: selectedItemValue[index].toString(),
      items: _dropDownItem(),
      onChanged: (value) {
        selectedItemValue[index] = value as String;
        setState(() {});
      },
    );
  }

  List<DropdownMenuItem<String>> _dropDownItem() {
    List<String> ddl = ["Not Done", "Partially Done", "Done"];
    return ddl
        .map((value) => DropdownMenuItem(
              value: value,
              child: Text(value),
            ))
        .toList();
  }
}

Answer 1

因为您使用的是index类的变量。

将索引传递到_Dropdown功能如下。

@override
Widget build(BuildContext context) {
  return Scaffold(
      appBar: AppBar(
        backgroundColor: const Color.fromRGBO(82, 113, 255, 25),
        title: Row(
          children: [
            Container(
                padding: const EdgeInsets.all(10.0),
                child: const Text('CHEKILI Table of Content'))
          ],
        ),
      ),
      body: Column(
        children: <Widget>[
          Flexible(
            child: ListView.builder(
              itemCount: propositions.length,
              itemExtent: 50.0,
              itemBuilder: (BuildContext context, int index) {
                for (int i = 0; i < propositions.length; i++) {
                  selectedItemValue.add("Not Done");
                }
                return ListTile(
                  title: Text("${propositions[index]}"),
                  leading: _dropdown(index), // <-- HERE
                );
              },
            ),
          ),
        ],
      ));
}

Widget _dropdown(int index) { // <-- HERE
  return DropdownButton<String>(
    isExpanded: false,
    value: selectedItemValue[index].toString(),
    items: _dropDownItem(),
    onChanged: (value) {
      selectedItemValue[index] = value as String;
      setState(() {});
    },
  );
}

其他注意事项：

不要将循环放置在列表中添加一些值，例如selectionItemvalue.add（“ not done”）; 在listView.builder中。

由于列表项目出现在屏幕上时，因此调用了构建器，因此selectedItemvalue将被添加过多。
因此，在initstate函数下启动列表如下。

@override
void initState() {
  super.initState();
  selectedItemValue.addAll(List.filled(propositions.length, "Not Done"));
}