flutter - 元素类型 'String'无法分配给列表类型 'DropdownMenuItem'

Question

我想用一些字符串填充Flutter中的DropdownButton，但出现错误
The element type 'String' can't be assigned to the list type 'DropdownMenuItem<String>'在使用字符串提交列​​表时

这是我的代码片段:

DropdownButton<String>(
  value: filter.getFilterPersonality(),
  onChanged: (String newValue){filter.setFilterPersonality(newValue);},
  items: ["-"],
),

我究竟做错了什么？

Answer 1

items应该是List的DropdownMenuItem<String>，而不是仅带有“-”的List<String>。

DropdownButton<String>(
      value: dropdownValue,
      icon: Icon(Icons.arrow_downward),
      iconSize: 24,
      elevation: 16,
      style: TextStyle(color: Colors.deepPurple),
      underline: Container(
        height: 2,
        color: Colors.deepPurpleAccent,
      ),
      onChanged: (String newValue) {
        setState(() {
          dropdownValue = newValue;
        });
      },
      items: <String>['One', 'Two', 'Free', 'Four']
          .map<DropdownMenuItem<String>>((String value) {
        return DropdownMenuItem<String>(
          value: value,
          child: Text(value),
        );
      }).toList(),
    );

看这里:
https://api.flutter.dev/flutter/material/DropdownMenuItem/DropdownMenuItem.html