在Flutter中如何给下拉按钮赋值？

0qx6xfy6 于 2023-02-16 发布在 Flutter

关注(0)|答案(2)|浏览(151)

假设您有一个来自API字符串列表，现在您希望在DropdownButton中显示该列表，假设您的列表如下所示

homepage_categories": [
    {
    "id": 1,
    "name": "Electronics",
    "slug": "electronics",
    "icon": "fas fa-anchor",
    "image": "uploads/custom-images/electronics-2022-11-19-02-48-28-5548.png"
    },
    {
    "id": 2,
    "name": "Game",
    "slug": "game",
    "icon": "fas fa-gamepad",
    "image": "uploads/custom-images/game-2022-11-19-02-48-48-6382.png"
    },
    {
    "id": 3,
    "name": "Mobile",
    "slug": "mobile",
    "icon": "fas fa-mobile-alt",
    "image": "uploads/custom-images/mobile-2022-11-19-02-49-20-2538.png"
    },
    {
    "id": 4,
    "name": "Lifestyle",
    "slug": "lifestyle",
    "icon": "fas fa-home",
    "image": "uploads/custom-images/lifestyle-2022-11-19-02-49-38-3139.png"
    },
]

从这个API你可以很容易地获取.

因此，问题是如何将默认/初始值（如“选择类别”或其他值）分配到该列表中

我试过了...

late List<CategoryModel> category;
  late String value;

  @override
  void initState() {
    category = context.read<CategoryBrandCubit>().categoryBrandModel.category;
    value = category.first.id.toString();
    super.initState();
  }

DropdownButton<String>(
          hint: const Text('Select Status'),
          isExpanded: true,
          icon: const Icon(Icons.keyboard_arrow_down_rounded),
          underline: const SizedBox(),
          value: value,
          onChanged: (String? val) {
            value = val!;
            bloc.add(StoreProductEventCategory(value));
            print('catVal: $value');
          },
        
          items: category
              .map(
                (e) => DropdownMenuItem<String>(
                  value: e.id.toString(),
                  child: Text(e.name),
                ),
              )
              .toList(),
        ),

flutter

来源：https://stackoverflow.com/questions/75451326/how-to-assign-initial-value-in-dropdownbutton-in-flutter

2条答案

按热度按时间

knpiaxh11#

试试这个：

DropdownButton<String>(
                            hint: const Text('Select Status'),
                            isExpanded: true,
                            icon: const Icon(
                                Icons.keyboard_arrow_down_rounded),
                            underline: const SizedBox(),
                            value: "default",
                            onChanged: (String? val) {},
                            items: [
                              const DropdownMenuItem(
                                alignment: Alignment.center,
                                value: "default",
                                enabled: false,
                                child: Text("Select Your role"),
                              ),
                              ...category
                                  .map(
                                    (e) => DropdownMenuItem<String>(
                                      value: e.id.toString(),
                                      child: Text(e.name),
                                    ),
                                  )
                                  .toList()
                            ],
                          ),

赞(0）回复(0）举报 2023-02-16

bn31dyow2#

DropdownButton的默认值对应于value字段。如果我们看一下代码，我们会发现您分配了值，但它是空的：

late String value; // this is empty

DropdownButton<String>(
          hint: const Text('Select Status'),
          isExpanded: true,
          icon: const Icon(Icons.keyboard_arrow_down_rounded),
          underline: const SizedBox(),
          value: value, // always the current value
          onChanged: (String? val) {
            value = val!;
            bloc.add(StoreProductEventCategory(value));
            print('catVal: $value');
          },

你要做的就是给value赋一个初始值，你可以这样做：value = homepage_categories[0].name
如果您看一下官方的flutter文档，您还可以看到value字段的描述如下：
value → T？：当前选定下拉菜单项的值。
您可以阅读更多关于它的内容here并查看完整的示例。

赞(0）回复(0）举报 2023-02-16

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在Flutter中如何给下拉按钮赋值？

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