【发布时间】：2020-12-14 10:48:25
【问题描述】：
我对 Flutter 和 Firestore 非常陌生。所以我在 Firebase 存储上上传了一些照片。 Here is how storage looks
然后我将他们的下载 URL 粘贴到 firestore 数据库中。 Here is how firestore looks
但每次我尝试将它们放入我的应用程序时，我都会收到以下错误
════════ 小部件库捕获的异常══════════════════════════════ ════ 'package:flutter/src/painting/_network_image_io.dart'：断言失败：第 26 行 pos 14：'url != null'：不正确。 相关的导致错误的小部件是 未来建造者 但是其他数据正在读取并显示在小部件中。 这是我的代码：
import 'package:flutter/material.dart';
import 'package:hexcolor/hexcolor.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:dotted_line/dotted_line.dart';
class CourseList extends StatefulWidget {
@override
_CourseListState createState() => _CourseListState();
}
class _CourseListState extends State<CourseList> {
@override
Widget build(BuildContext context) {
return FutureBuilder(
future: FirebaseFirestore.instance
.collection('students')
.doc(FirebaseAuth.instance.currentUser.uid)
.get(),
builder: (BuildContext context, snapshot) {
if (snapshot.hasData) {
Map<String, dynamic> documentFields = snapshot.data.data();
return ListView(
shrinkWrap: true,
children: [
Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Stack(
overflow: Overflow.visible,
children: [
Positioned(
// top: 0,
child: Padding(
padding: const EdgeInsets.fromLTRB(0, 10, 0, 0),
child: Container(
width: 430,
height: 230,
decoration: BoxDecoration(
image: DecorationImage(
image: AssetImage("assets/hero.png"),
fit: BoxFit.cover,
),
),
),
),
),
Positioned(
top: 200,
left: 20,
right: 20,
child: Card(
color: Hexcolor('#3B3E43'),
elevation: 10,
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(10.0),
),
child: Padding(
padding: const EdgeInsets.all(15),
child: Column(
children: [
Text(
'Welcome to Class Information System',
textAlign: TextAlign.center,
style: TextStyle(
color: Colors.white,
fontFamily: 'ProductSans',
fontSize: 16,
fontWeight: FontWeight.bold,
),
),
SizedBox(
height: 10,
),
Text(
'UTM Class Management system offers UTM students a varity of features such as, managing and making real time class schedule, finding class venue with dynamic maps and finding all the lecturers office, phone and email all at one place!',
textAlign: TextAlign.center,
style: TextStyle(
color: Colors.grey[300],
fontFamily: 'ProductSans',
fontSize: 11,
),
),
SizedBox(
height: 15,
),
Column(
children: [
Row(
mainAxisAlignment:
MainAxisAlignment.spaceEvenly,
children: [
Image.asset(
'assets/001-school.png',
scale: 8,
),
SizedBox(
width: 0,
),
Image.asset(
'assets/002-teacher.png',
scale: 8,
),
SizedBox(
width: 0,
),
Image.asset(
'assets/003-calendar.png',
scale: 8,
),
],
),
SizedBox(
height: 10,
),
Row(
mainAxisAlignment:
MainAxisAlignment.spaceEvenly,
children: [
Text(
'Finding class\nvenue with\ndynamic maps',
textAlign: TextAlign.center,
style: TextStyle(
color: Colors.grey[300],
fontFamily: 'ProductSans',
fontSize: 10,
),
),
Text(
'Finding all the\nlecturers informations\nat one place!',
textAlign: TextAlign.center,
style: TextStyle(
color: Colors.grey[300],
fontFamily: 'ProductSans',
fontSize: 10,
),
),
Text(
'Make & Edit\nreal time\nclass schedule',
textAlign: TextAlign.center,
style: TextStyle(
color: Colors.grey[300],
fontFamily: 'ProductSans',
fontSize: 10,
),
),
],
),
],
)
],
),
),
),
),
],
),
SizedBox(
height: 220,
),
Padding(
padding: const EdgeInsets.fromLTRB(25, 10, 0, 0),
child: Text(
'Courses Taken',
textAlign: TextAlign.left,
style: TextStyle(
color: Hexcolor('#E69405'),
fontFamily: 'ProductSans',
fontSize: 18,
),
),
),
Padding(
padding: const EdgeInsets.fromLTRB(25, 10, 25, 5),
child: DottedLine(
direction: Axis.horizontal,
lineLength: double.infinity,
lineThickness: 1.0,
dashLength: 4.0,
dashColor: Hexcolor('#707070'),
dashRadius: 0.0,
dashGapLength: 6.0,
dashGapColor: Colors.transparent,
dashGapRadius: 0.0,
),
),
SizedBox(
height: 15,
),
Card(
color: Hexcolor('#3B3E43'),
elevation: 10,
margin: EdgeInsets.fromLTRB(25, 0, 25, 20),
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(10.0),
),
child: Padding(
padding: const EdgeInsets.all(15),
child: ListView(
physics: ClampingScrollPhysics(),
shrinkWrap: true,
children: [
Row(
children: [
Expanded(
child: Padding(
padding:
const EdgeInsets.fromLTRB(10, 0, 0, 0),
child: CircleAvatar(
backgroundImage:
NetworkImage(documentFields['img1']),
radius: 28,
),
),
),
Expanded(
flex: 4,
child: Padding(
padding:
const EdgeInsets.fromLTRB(20, 0, 0, 0),
child: RichText(
text: TextSpan(
style: TextStyle(
fontFamily: 'ProductSans',
fontSize: 17,
),
text: documentFields['course1'],
children: <TextSpan>[
TextSpan(
text:
'\nSection: ${documentFields['section1']}',
style: TextStyle(
fontFamily: 'ProductSans',
fontSize: 14,
color: Colors.grey[400],
),
),
],
),
),
),
),
],
),
SizedBox(
height: 15,
),
DottedLine(
direction: Axis.horizontal,
lineLength: double.infinity,
lineThickness: 1.0,
dashLength: 10,
dashColor: Hexcolor('#707070'),
dashRadius: 0.0,
dashGapLength: 0,
dashGapColor: Colors.transparent,
dashGapRadius: 0.0,
),
SizedBox(
height: 15,
),
Row(
children: [
Expanded(
child: Padding(
padding:
const EdgeInsets.fromLTRB(10, 0, 0, 0),
child: CircleAvatar(
child: Image.network(
'${documentFields['img2']}'),
radius: 28,
),
),
),
Expanded(
flex: 4,
child: Padding(
padding:
const EdgeInsets.fromLTRB(20, 0, 0, 0),
child: RichText(
text: TextSpan(
style: TextStyle(
fontFamily: 'ProductSans',
fontSize: 17,
),
text: documentFields['course2'],
children: <TextSpan>[
TextSpan(
text:
'\nSection: ${documentFields['section2']}',
style: TextStyle(
fontFamily: 'ProductSans',
fontSize: 14,
color: Colors.grey[400],
),
),
],
),
),
),
),
],
),
SizedBox(
height: 15,
),
DottedLine(
direction: Axis.horizontal,
lineLength: double.infinity,
lineThickness: 1.0,
dashLength: 10,
dashColor: Hexcolor('#707070'),
dashRadius: 0.0,
dashGapLength: 0,
dashGapColor: Colors.transparent,
dashGapRadius: 0.0,
),
SizedBox(
height: 15,
),
Row(
children: [
Expanded(
child: Padding(
padding:
const EdgeInsets.fromLTRB(10, 0, 0, 0),
child: CircleAvatar(
child: Image.network(
'${documentFields['img3']}'),
radius: 28,
),
),
),
Expanded(
flex: 4,
child: Padding(
padding:
const EdgeInsets.fromLTRB(20, 0, 0, 0),
child: RichText(
text: TextSpan(
style: TextStyle(
fontFamily: 'ProductSans',
fontSize: 17,
),
text: documentFields['course3'],
children: <TextSpan>[
TextSpan(
text:
'\nSection: ${documentFields['section3']}',
style: TextStyle(
fontFamily: 'ProductSans',
fontSize: 14,
color: Colors.grey[400],
),
),
],
),
),
),
),
],
),
SizedBox(
height: 15,
),
DottedLine(
direction: Axis.horizontal,
lineLength: double.infinity,
lineThickness: 1.0,
dashLength: 10,
dashColor: Hexcolor('#707070'),
dashRadius: 0.0,
dashGapLength: 0,
dashGapColor: Colors.transparent,
dashGapRadius: 0.0,
),
SizedBox(
height: 15,
),
Row(
children: [
Expanded(
child: Padding(
padding:
const EdgeInsets.fromLTRB(10, 0, 0, 0),
child: CircleAvatar(
child: Image.network(
'${documentFields['img4']}'),
radius: 28,
),
),
),
Expanded(
flex: 4,
child: Padding(
padding:
const EdgeInsets.fromLTRB(20, 0, 0, 0),
child: RichText(
text: TextSpan(
style: TextStyle(
fontFamily: 'ProductSans',
fontSize: 17,
),
text: documentFields['course4'],
children: <TextSpan>[
TextSpan(
text:
'\nSection: ${documentFields['section4']}',
style: TextStyle(
fontFamily: 'ProductSans',
fontSize: 14,
color: Colors.grey[400],
),
),
],
),
),
),
),
],
),
],
),
),
)
],
),
],
);
}
return Center(child: CircularProgressIndicator());
},
);
}
}
任何帮助将不胜感激。谢谢！
【问题讨论】：
-
如果您手动设置url字符串，您的代码是否有效？
-
是的，它正在工作
-
我在question上发现了类似的代码问题
标签： flutter flutter-futurebuilder