英文:
How to skip Null value from List<dynamic> in flutter
问题
以下是您提供的代码的中文翻译：
// 忽略文件的警告: prefer_const_constructors, prefer_const_literals_to_create_immutables
import 'package:campuslib/controllers/content_controller.dart';
import 'package:campuslib/utils/colors.dart';
import 'package:campuslib/utils/dimensions.dart';
import 'package:campuslib/utils/routers.dart';
import 'package:campuslib/widgets/big_text.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:get/get.dart';
class DepartmentBody extends StatefulWidget {
const DepartmentBody({Key? key}) : super(key: key);
@override
State<DepartmentBody> createState() => _DepartmentBodyState();
}
class _DepartmentBodyState extends State<DepartmentBody> {
final ContentController _contentController = Get.put(ContentController());
late Map<String, String> deptFullName = {
"cse": "计算机科学与工程",
"eee": "电气与电子工程",
"math": "数学",
"sta": "统计学",
"nonacademic": "非学术",
"islamic": "伊斯兰学",
"acce": "应用化学与化学工程",
};
@override
Widget build(BuildContext context) {
return Obx(() {
if (!(_contentController.dept.value.data != null)) {
return CircularProgressIndicator();
} else {
var deptList = _contentController.dept.value.data?.getDepartments;
return _initDeptBody(deptList);
}
});
}
Widget _initDeptBody(var deptList) {
return Expanded(
child: Column(
children: [
SizedBox(
height: 20,
),
BigText(
text: "部门",
fontWeight: FontWeight.bold,
size: 20,
),
Obx(() => (!_contentController.isLoadingForDept.value)
? Expanded(
child: Container(
padding: EdgeInsets.fromLTRB(20, 15, 20, 0),
decoration: BoxDecoration(
borderRadius: BorderRadius.only(
topLeft: Radius.circular(40),
topRight: Radius.circular(40),
),
),
child: ListView.builder(
itemCount: deptList?.length,
padding: EdgeInsets.zero,
physics: BouncingScrollPhysics(),
shrinkWrap: true,
itemBuilder: (context, index) =>
_buildDepartmentItem(deptList, index),
),
),
)
: CircularProgressIndicator())
],
),
);
}
Widget _buildDepartmentItem(var deptList, int index) {
final String? currentString = deptList[index];
if (currentString != null) {
return Container(
height: Dimension.deptNameContainer(context),
margin: EdgeInsets.fromLTRB(0, 0, 0, 20),
child: ClipRRect(
borderRadius: BorderRadius.circular(15),
child: Stack(
alignment: AlignmentDirectional.center,
children: [
Container(
width: MediaQuery.of(context).size.width,
decoration: BoxDecoration(
image: DecorationImage(
fit: BoxFit.cover,
image: AssetImage("assets/images/${deptList[index]}.jpg"),
),
),
),
Card(
elevation: 0.0,
margin: EdgeInsets.zero,
color: Color.fromARGB(202, 25, 24, 24),
child: Container(
height: MediaQuery.of(context).size.height,
width: MediaQuery.of(context).size.width,
child: InkWell(
onTap: () {
// 导航到部门路线
Get.toNamed(MyRouters.departmentRoute, arguments: {
"deptBanner": deptList[index],
"deptName": deptFullName[deptList[index]],
});
},
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
ListTile(
title: Text(
deptFullName[deptList?[index]]!,
textAlign: TextAlign.center,
style: TextStyle(
color: AppColors.lightColor,
fontWeight: FontWeight.w500,
// fontSize: 18,
),
),
),
],
),
),
),
),
],
),
),
);
} else {
return Container();
}
}
}
希望这个翻译对您有所帮助。如果您需要任何进一步的协助，请随时告诉我。
英文:
Summary:<br/>
I have a List of dynamic data such as {"CSE", "EEE", null, "ACCE"}.
Now I want to show these data through ListView builder except the null.
But I can't skip the null value. It gives:
Exception has occurred. (type 'Null' is not a subtype of type 'String' in type cast)
My code is given below and I tried other method too, which I give in the screenshots.
// ignore_for_file: prefer_const_constructors, prefer_const_literals_to_create_immutables
import 'package:campuslib/controllers/content_controller.dart';
import 'package:campuslib/utils/colors.dart';
import 'package:campuslib/utils/dimensions.dart';
import 'package:campuslib/utils/routers.dart';
import 'package:campuslib/widgets/big_text.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:get/get.dart';
class DepartmentBody extends StatefulWidget {
const DepartmentBody({Key? key}) : super(key: key);
@override
State<DepartmentBody> createState() => _DepartmentBodyState();
}
class _DepartmentBodyState extends State<DepartmentBody> {
final ContentController _contentController = Get.put(ContentController());
late Map<String, String> deptFullName = {
"cse": "Computer Science and Engineering",
"eee": "Electrical and Electronic Engineering",
"math": "Mathematics",
"sta": "Statistics",
"nonacademic": "Non Academic",
"islamic": "Islamic",
"acce": "Applied Chemistry & Chemical Engineering",
};
@override
Widget build(BuildContext context) {
return Obx(() {
if (!(_contentController.dept.value.data != null)) {
return CircularProgressIndicator();
} else {
var deptList = _contentController.dept.value.data?.getDepartments;
return _initDeptBody(deptList);
}
});
}
Widget _initDeptBody(var deptList) {
return Expanded(
child: Column(
children: [
SizedBox(
height: 20,
),
BigText(
text: "Departments",
fontWeight: FontWeight.bold,
size: 20,
),
Obx(() => (!_contentController.isLoadingForDept.value)
? Expanded(
child: Container(
padding: EdgeInsets.fromLTRB(20, 15, 20, 0),
decoration: BoxDecoration(
borderRadius: BorderRadius.only(
topLeft: Radius.circular(40),
topRight: Radius.circular(40),
),
),
child: ListView.builder(
itemCount: deptList?.length,
padding: EdgeInsets.zero,
physics: BouncingScrollPhysics(),
shrinkWrap: true,
itemBuilder: (context, index) =>
_buildDepartmentItem(deptList, index),
),
),
)
: CircularProgressIndicator())
],
),
);
}
Widget _buildDepartmentItem(var deptList, int index) {
final String? currentString = deptList[index];
if (currentString != null) {
return Container(
height: Dimension.deptNameContainer(context),
margin: EdgeInsets.fromLTRB(0, 0, 0, 20),
child: ClipRRect(
borderRadius: BorderRadius.circular(15),
child: Stack(
alignment: AlignmentDirectional.center,
children: [
Container(
width: MediaQuery.of(context).size.width,
decoration: BoxDecoration(
image: DecorationImage(
fit: BoxFit.cover,
image: AssetImage("assets/images/${deptList[index]}.jpg"),
),
),
),
Card(
elevation: 0.0,
margin: EdgeInsets.zero,
color: Color.fromARGB(202, 25, 24, 24),
child: Container(
height: MediaQuery.of(context).size.height,
width: MediaQuery.of(context).size.width,
child: InkWell(
onTap: () {
// Navigator.name(context, MyRouters.departmentRoute);
Get.toNamed(MyRouters.departmentRoute, arguments: {
"deptBanner": deptList[index],
"deptName": deptFullName[deptList[index]],
});
},
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
ListTile(
title: Text(
deptFullName[deptList?[index]]!,
textAlign: TextAlign.center,
style: TextStyle(
color: AppColors.lightColor,
fontWeight: FontWeight.w500,
// fontSize: 18,
),
),
),
],
),
),
),
),
],
),
),
);
} else {
return Container();
}
}
}
Screenshots:
Flutter doctor:
答案1
得分: 1
你可以筛选掉空值，将它们转换为列表，如下所示：
List<String> validDeptList = deptList?.where((dept) => dept != null).toList() ?? [];
以这种方式，validDeptList 只包含非空值。
英文:
You can filter the null value to cast them in the list like
List<String> validDeptList = deptList?.where((dept) => dept != null).toList() ?? [];
In this form, validDeptList have only non-null values.
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