SetState不更新对话框

我正在尝试为用户填写费用表格，我想获取费用类别。我已经创建了包含所有项目和所有项目的下拉按钮，但是我希望用户能够输入自定义类别。为此，我创建了一个名为other的类别，当用户单击该类别时，下拉按钮将替换为TextField和Icon按钮，如果用户选择改为选择该类别，则再次显示Dropdown。除“图标”按钮外，其他所有功能均正常。它什么也没做，有人可以向我解释为什么吗？

码：

import 'package:flutter/material.dart';

class UserPage extends StatefulWidget {
  @override
  _UserPageState createState() => _UserPageState();
}

class _UserPageState extends State<UserPage> {
  List<List> categories = [
    ['food', Icon(Icons.fastfood)],
    ['clothing', Icon(Icons.shopping_basket)],
    ['electronics', Icon(Icons.computer)],
    ['accessories', Icon(Icons.blur_circular)],
    ['transportation', Icon(Icons.local_taxi)],
    ['gain', Icon(Icons.attach_money)],
    ['other', Icon(Icons.radio_button_unchecked)]
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text('Add Purchase Dialog'),
        ),
        body: Center(
            child: IconButton(
          icon: Icon(Icons.add_circle),
          onPressed: () {
            createPurchase(context);
          },
        )));
  }

  void createPurchase(BuildContext context) {
    final _formKey = GlobalKey<FormState>();
    final priceController = TextEditingController();
    final otherCategoryController = TextEditingController();

    var _selectedCategory;
    bool otherSelected = false;
    double dialogHeight = 187;

    List<DropdownMenuItem> menuItems = [];
    for (var category in categories) {
      menuItems.add(DropdownMenuItem(
          value: (category[0] != 'other')
              ? category[0]
              : otherCategoryController.text,
          child: Row(
            children: <Widget>[
              category[1],
              SizedBox(width: 5),
              Text(category[0]),
            ],
          )));
    }

    showDialog(
        context: context,
        builder: (context) => Dialog(
              shape: RoundedRectangleBorder(
                  borderRadius: BorderRadius.circular(20.0)),
              child: StatefulBuilder(
                builder: (BuildContext context, StateSetter setState) {
                  return Container(
                    padding: EdgeInsets.fromLTRB(20, 10, 20, 0),
                    height: dialogHeight,
                    width: 300,
                    child: Column(
                      children: <Widget>[
                        Text('Add a purchase'),
                        Form(
                          key: _formKey,
                          child: Column(
                            mainAxisAlignment: MainAxisAlignment.center,
                            children: <Widget>[
                              otherSelected
                                  ? Row(
                                      children: <Widget>[
                                        SizedBox(
                                            width: 184,
                                            height: 20,
                                            child: TextFormField(
                                              controller:
                                                  otherCategoryController,
                                              decoration: InputDecoration(
                                                  hintText: 'Other Category'),
                                            )),
                                        IconButton(
                                            icon: Icon(Icons.arrow_drop_down),
                                            onPressed: () {
                                              setState() => otherSelected =
                                                  !otherSelected;
                                            })
                                      ],
                                    )
                                  : DropdownButtonFormField(
                                      hint: Text('Category'),
                                      items: menuItems,
                                      onChanged: (category) => setState(() {
                                        _selectedCategory = category;
                                        (category == 'other')
                                            ? otherSelected = true
                                            : null;
                                      }),
                                      value: _selectedCategory,
                                      validator: (val) => (val == null)
                                          ? 'Select a category'
                                          : null,
                                    ),
                              TextFormField(
                                decoration: InputDecoration(hintText: 'Amount'),
                                controller: priceController,
                                keyboardType: TextInputType.number,
                                validator: (val) =>
                                    (val == null) ? 'enter an amount' : null,
                              ),
                              Row(
                                mainAxisAlignment: MainAxisAlignment.end,
                                children: <Widget>[
                                  FlatButton(
                                      child: Text('Continue'), onPressed: null),
                                ],
                              ),
                            ],
                          ),
                        )
                      ],
                    ),
                  );
                },
              ),
            ));
  }
}

非常感谢您的帮助。