Query Firestore和Streambuilder()的Flutter Firebase问题

Question

我正在尝试搜索与TextField中的文本匹配的文档，并使用Streambuilder显示它们。由于我是一个颤振初学者，我没有找到关于如何做到这一点的有用视频和教程。

我正试着做这样的事情：

Widget body(BuildContext context) {
if(textControllerSearch.text != "") {
if(textFocusNodeSearch.hasFocus == false) {
return ClipRRect(
borderRadius: BorderRadius.all(Radius.circular(15)),
child: StreamBuilder<QuerySnapshot>(
stream: FirebaseFirestore.instance
.collection('users')
.doc(firebaseUser!.uid.toString())
.collection("recipes")
.where("recipeName", arrayContains: textControllerSearch.text.trim())
.limit(3)
.snapshots(),
builder: (context, snapshot) {
return ListView.builder(
itemCount: snapshot.data!.docs.length,
itemBuilder: (context, index) {
DocumentSnapshot documentSnapshot = snapshot.data!.docs[index];
return ListTile(title: Text(documentSnapshot['recipeName']));
});
},
),
);
} else {
return Container(
alignment: Alignment.topCenter,
child: Column(
mainAxisAlignment: MainAxisAlignment.start,
children: [
Container(
child: Lottie.asset("assets/lottie/search_bubble.json", width: MediaQuery.of(context).size.width * 0.5, fit: BoxFit.fitWidth),
),
Container(
child: Text(
"Searching...",
textAlign: TextAlign.center,
style: TextStyle(
color: Color(0xFFEC8E00).withOpacity(0.5),
fontSize: 10,
),
),
),
],
),
);
}
} else {
return Container();
}
}

文本字段：

TextFormField(
focusNode: textFocusNodeSearch,
textAlign: TextAlign.left,
keyboardType: TextInputType.name,
controller: textControllerSearch,
autofocus: true,
onFieldSubmitted: (value) {
setState(() {});
},
onChanged: (value) {
if(textControllerSearch.text.trim() == "") {
setState(() {
notSearching = true;
});
} else {
setState(() {
notSearching = false;
});
}
},
style: TextStyle(
fontFamily: 'Font',
fontSize: 16,
color: Colors.white.withOpacity(0.75),
),
obscureText: false,
cursorColor: Color(0xFFEC8E00),
decoration: InputDecoration(
border: InputBorder.none,
hintText: 'Search',
hintStyle: TextStyle(
fontSize: 14,
color: Colors.white.withOpacity(0.75),
fontFamily: 'Font',
),
),
),

我得到了这个错误，但我不能清楚地理解什么是错误以及是什么导致了问题：

The following _CastError was thrown building StreamBuilder<QuerySnapshot<Object?>>(dirty, state: _StreamBuilderBaseState<QuerySnapshot<Object?>, AsyncSnapshot<QuerySnapshot<Object?>>>#6bf78):
Null check operator used on a null value

Answer 1

根据您的日志，错误在这里：

child: StreamBuilder<QuerySnapshot>(
stream: FirebaseFirestore.instance
.collection('users')
.doc(firebaseUser!.uid.toString())
.collection("recipes")
.where("recipeName", arrayContains: textControllerSearch.text.trim())
.limit(3)
.snapshots(),
builder: (context, snapshot) {
return ListView.builder(
itemCount: snapshot.data!.docs.length,
itemBuilder: (context, index) {
DocumentSnapshot documentSnapshot = snapshot.data!.docs[index];
return ListTile(title: Text(documentSnapshot['recipeName']));
});

你设置好了！在snapshot.data上，检查snapshot.ddata是否与null不同。

Answer 2

这是因为某个地方有一个null值。尝试更换

return ListView.builder(
itemCount: snapshot.data!.docs.length,
itemBuilder: (context, index) {
DocumentSnapshot documentSnapshot = snapshot.data!.docs[index];
return ListTile(title: Text(documentSnapshot['recipeName']));
});

带snapshot.data?.docs[index];

Answer 3

child: StreamBuilder<QuerySnapshot>(
stream: FirebaseFirestore.instance
.collection('users')
.doc(firebaseUser!.uid.toString())
.collection("recipes")
.where("recipeName", arrayContains: textControllerSearch.text.toString().trim()) //add toString()
.limit(3)
.snapshots(),
builder: (context, snapshot) {
return ListView.builder(
itemCount: snapshot.data!.docs.length,
itemBuilder: (context, index) {
DocumentSnapshot documentSnapshot = snapshot.data!.docs[index];
return ListTile(title: Text(documentSnapshot['recipeName'].toString())); //add toString()
});