Flutter-下拉值 [英] Flutter - Dropdown value

问题描述

我需要在flutter下拉列表中使用字符串作为值。但是返回

I need use a string as a value in the flutter dropdown. But returns

引发了另一个异常：
'package：flutter / src / material / dropdown.dart'：失败的断言：行
609 pos 15：'items == null || items.isEmpty ||值== null ||
items.where（（（DropdownMenuItem item）=> item.value == value）.length
== 1'：不正确。

Another exception was thrown: 'package:flutter/src/material/dropdown.dart': Failed assertion: line 609 pos 15: 'items == null || items.isEmpty || value == null || items.where((DropdownMenuItem item) => item.value == value).length == 1': is not true.

完整日志此处。

代码为

items: dataMaker.map((item) {
                          return new DropdownMenuItem<String>(
                            child: new Text(item['fabricante'],
                                textAlign: TextAlign.center),
                            value: item['fabricante'], //FAIL
                          );
                        }).toList(),

所以我的问题在：如何使用字符串作为项目值？另一个解决方案是获取下拉菜单中的文本，但我不知道该怎么做。

So my question in: How can i use a string as item value? Another solution is get the text of dropdown but i don´t know how.

-解决方案-

使用此代码，我可以在dataMaker列表中找到与下拉菜单具有相同文本的所有元素。

With this code I can find all the elements in the dataMaker list that have the same text as the drop-down menu.

 var test =dataMaker.firstWhere((fabricante) => fabricante["id"].toString() == dropdownSelectionMaker);              
 dataModelo = dataMaker.where((modelo) => modelo["fabricante"] == test["fabricante"]).toList();   

推荐答案

我不确定库如何进行比较但我发现尽管该值在他的列表中，但仍返回错误，因此我不得不进行一些手动比较。注意： BuildingType 只是一个自定义数据类型。
这是我的案例的神奇之处：
value：selectedType == null吗？ selectedType：buildingTypes.where（（i）=> i.name == selectedType.name）。首先作为BuildingType，

I'm not sure how the library does the comparison but I found that though the value was in he list it still returned the error, so I had to do some manual comparison. NOTE: BuildingType is just a custom data type. Here's the magical line for my case: value: selectedType == null ? selectedType : buildingTypes.where( (i) => i.name == selectedType.name).first as BuildingType,

return DropdownButton<T>(
  hint: Text("Select Building type"),
  value: selectedType == null ? selectedType : buildingTypes.where( (i) => i.name == selectedType.name).first as BuildingType,
  onChanged: handleBuildingTypeChange,
  items: abcList.map((T value) {
    return DropdownMenuItem<T>(
      value: value,
      child: Row(
        children: <Widget>[
          SizedBox(
            width: 10,
          ),
          Text(
            value.name,
            style: TextStyle(color: Colors.black),
          ),
        ],
      ),
    );
  }).toList(),
);

这篇关于Flutter-下拉值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！