我对 Flutter 和 Firestore 很陌生。所以我在 Firebase 存储上上传了一些照片。 这是存储的外观
然后我将他们的下载 URL 粘贴到 firestore 数据库中。 这是firestore的样子
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═════════════════════════════␕═'包════' :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 FutureBuilder 但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！