jsonapi的flutter下拉列表 [英] flutter dropdown from jsonapi

问题描述

此代码运行正常，并在列表视图中显示数据:

This code is working perfectly fine and showing data in listview:

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,
                              ),
                             
                            );
                          });

但是当我在下拉窗口小部件中使用它时，它会抛出错误:

but when I am using the same in dropdown widget, it is throwing error:

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'

但是在列表视图生成器中，我得到以下结果:

but in listview builder I am getting this result:

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:

I used to add a custom value in dropdown list like this:

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

，另一个将显示在下拉列表中.

and the other will show up in the dropdownlist.

但是当我尝试使用当前的未来方法时

but when I am trying in the present future method

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');
    }
  }

但是在这里我得到了一个错误-未为类型'Future'定义方法'add'.

but here I am getting the error - The method 'add' isn't defined for the type 'Future'.

推荐答案

更改此内容

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

对此:

 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');
    }

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