Question

此代码运行良好并在列表视图中显示数据：

return ListView.builder(
                          itemCount: snapshot.data.data.length,
                          itemBuilder: (context, index) {
                            print(snapshot.data.data[index]);
                            return ListTile(
                              title:
                                Text(snapshot.data.data[index].id.toString()),
                              subtitle: Text(
                                snapshot.data.data[index].attributes.name==null?'Not Set':snapshot.data.data[index].attributes.name,
                              ),
                             
                            );
                          });

但是当我在下拉小部件中使用相同的时，它会抛出错误：

return DropdownButton<String>(
                     hint: Text("Select"),
                     value: _selectedTestkit,
                     onChanged: (newValue) {
                     setState(() {
                     _selectedTestkit = newValue;
                                              });
                                            },
    items: snapshot.data.data.map((item) =>
    DropdownMenuItem<String>(
              child: Text(item.id),
                value:item.id,
        )).toList(),
                                          );
                                        }
                                    }
                                  }),
                            ),

这是我得到的错误：

There should be exactly one item with [DropdownButton]'s value: . 
Either zero or 2 or more [DropdownMenuItem]s were detected with the same value
'package:flutter/src/material/dropdown.dart':
Failed assertion: line 855 pos 15: 'items == null || items.isEmpty || value == null ||
              items.where((DropdownMenuItem<T> item) {
                return item.value == value;
              }).length == 1'

但在列表视图构建器中我得到了这个结果：

1 testname1
2 testname2
3 testname3
4 testname4

更新：

我曾经在下拉列表中添加自定义值，如下所示：

List data = json.decode(response.body);
data.add('other');

另一个将显示在下拉列表中。

但是当我尝试现在的未来方法时

Future<TestkitList> fetchTestkitId() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();    
    Uri testkiturl = Uri.https(staging_url, "testkits");
    
    final response = await http.get(testkiturl, headers: {
      'Accept-Type': 'application/json',
      "Content-Type": "application/json",      

    if (response.statusCode == 200) {
      // If the server did return a 200 OK response,
      // then parse the JSON.
      print(response.body);
      print('this was printed before json decode');
      var responsetestkit = Future.value(testkitListFromMap(response.body));

      responsetestkit.add('other');//here I am trying to add a custom item for dropdown
      setState(() {
        _testkit = responsetestkit;
        print(_testkit);
      });
    } else {
      // If the server did not return a 200 OK response,
      // then throw an exception.
      print(response.body);
      throw Exception('Failed to load TESTKITLIST');
    }
  }

但在这里我收到错误 - The method 'add' isn't defined for the type 'Future'.

Answer 1

改变这个

 if (response.statusCode == 200) {      
      return Future.value(testkitListFromMap(response.body));
    } else {     
      throw Exception('Failed to load TESTKITLIST');
    }

为此：

 if (response.statusCode == 200) {      
      return Future.value(testkitListFromMap(response.body["data"]));//you need to add "data" to access your items based on your data class.
    } else {     
      throw Exception('Failed to load TESTKITLIST');
    }

来自 jsonapi 的颤振下拉菜单

1 个答案: