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[英]Firebase Flutter Dart :Class '_JsonQuerySnapshot' has no instance method '[]'. Receiver: Instance of '_JsonQuerySnapshot'
[英]dart/flutter - Class 'Datum' has no instance method '[]'
我有一個 Podo class,它從 API 獲取數據。 那工作正常。 在下拉字段中,我使用 id 的值並顯示名稱。
來自 api 響應的示例 Json 數據如下所示:
{"jsonapi":{"version":"1.0"},"data":[{"type":"testkit","id":"1","attributes":{"active":true,"testType":"type1","code":"T101","name":"TestName1","infos":{},}},{"type":"testkit","id":"2","attributes":{"active":true,"testType":"type2","code":"T102","name":"TestName2","productId":null,"infos":{}}}]}
對於快照:
child: FutureBuilder(
future: _testkit,
builder: (context,
AsyncSnapshot<TestkitList> snapshot) {
drowdownFieldWidget 代碼如下:
DropdownButtonFormField<String>(
hint:Text("Select Testkit Name"),
value: _selectedTestkit,
onChanged: (newValue) {
setState(() {
_selectedTestkit = newValue;
_selectedTestType = getTestType()// this I am trying to get the value of test type, but not working.
});
},
validator: (value) => value ==
null
? 'Please select the Testkit'
: null,
items: (snapshot.data.data)
.map((item) =>
DropdownMenuItem<
String>(
child: Text(
item.attributes.name
.length >
30
? item
.attributes
.name
.substring(
0, 30)
: item
.attributes
.name,
),
value: item.id,
))
.toList(),
);
}
}
}),
)),
現在除了選中項的 id 外,我還需要訪問attributes
下testType
的值
我嘗試通過創建 function getTestType()
來訪問該值,如下所示:
getTestType() async {
final List testkits = await responsetestkit.then((value) => value.data);
print("below line is printed in function getTestType");
print(testkits.runtimeType);
print(testkits);
var testtype =
testkits.firstWhere((testkit) => testkit["id"] == _selectedTestkit);
print(testtype);
}
此 function 返回錯誤 - Class 'Datum' has no instance method '[]'.
如果需要任何進一步的信息,請告訴我。
更新:Podo 文件的內容:
import 'dart:convert';
TestkitList testkitListFromMap(String str) => TestkitList.fromMap(json.decode(str));
String testkitListToMap(TestkitList data) => json.encode(data.toMap());
class TestkitList {
TestkitList({
this.jsonapi,
this.data,
});
Jsonapi jsonapi;
List<Datum> data;
factory TestkitList.fromMap(Map<String, dynamic> json) => TestkitList(
jsonapi: json["jsonapi"] == null ? null : Jsonapi.fromMap(json["jsonapi"]),
data: json["data"] == null ? null : List<Datum>.from(json["data"].map((x) => Datum.fromMap(x))),
);
Map<String, dynamic> toMap() => {
"jsonapi": jsonapi == null ? null : jsonapi.toMap(),
"data": data == null ? null : List<dynamic>.from(data.map((x) => x.toMap())),
};
}
class Datum {
Datum({
this.type,
this.id,
this.attributes,
});
String type;
String id;
Attributes attributes;
factory Datum.fromMap(Map<String, dynamic> json) => Datum(
type: json["type"] == null ? null : json["type"],
id: json["id"] == null ? null : json["id"],
attributes: json["attributes"] == null ? null : Attributes.fromMap(json["attributes"]),
);
Map<String, dynamic> toMap() => {
"type": type == null ? null : type,
"id": id == null ? null : id,
"attributes": attributes == null ? null : attributes.toMap(),
};
}
class Attributes {
Attributes({
this.active,
this.testType,
this.code,
this.name,
this.infos,
});
bool active;
String testType;
首先,您將getTestType
方法標記為async
,然后它只返回一個Future
並且需要then
或await
來獲取值:
onChanged: (newValue) async {
_selectedTestkit = newValue;
_selectedTestType = await getTestType();
setState(() {});
},
其次, getTestType
方法不返回任何值。 修復添加返回值:
getTestType() async {
final List testkits = await responsetestkit.then((value) => value.data);
print("below line is printed in function getTestType");
print(testkits.runtimeType);
print(testkits);
var testtype =
testkits.firstWhere((testkit) => testkit["id"] == _selectedTestkit);
print(testtype);
return testtype;
}
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