我正在开发一个管理应用程序，因为我厌倦了从firebase返回用户数量，我从stackoverflow那里得到了很少的帮助，并且能够在终端上打印，但是在应用程序上返回null可以有人请帮助我。我的代码
class _AdminState extends State<Admin> {
Future<String> getUsersCount() async{
var length = -1;
await Firestore.instance.collection('users').getDocuments().then((myDocuments){
print("${myDocuments.documents.length}");
length = myDocuments.documents.length;
});
return Future.value(length.toString());
}
Page _selectedPage = Page.dashboard;
MaterialColor active = Colors.indigo;
MaterialColor notActive = Colors.grey;
final databaseReference = Firestore.instance;
bool isDelete= true;
var values;
TextEditingController categoryController = TextEditingController();
TextEditingController brandController = TextEditingController();
GlobalKey<FormState> _categoryFormKey = GlobalKey();
//GlobalKey<FormState> _brandFormKey = GlobalKey();
// BrandService _brandService = BrandService();
CategoryService _categoryService = CategoryService();
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Row(
children: <Widget>[
Expanded(
child: FlatButton.icon(
onPressed: () {
setState(() => _selectedPage = Page.dashboard);
},
icon: Icon(
Icons.dashboard,
color: _selectedPage == Page.dashboard
? active
: notActive,
),
label: Text('Dashboard'))),
Expanded(
child: FlatButton.icon(
onPressed: () {
setState(() => _selectedPage = Page.manage);
},
icon: Icon(
Icons.sort,
color:
_selectedPage == Page.manage ? active : notActive,
),
label: Text('Manage'))),
],
),
elevation: 0.0,
backgroundColor: Colors.white,
),
body: _loadScreen());
}
Widget _loadScreen() {
switch (_selectedPage) {
case Page.dashboard:
return FutureBuilder(
future: getUsersCount(),
builder: (BuildContext context, AsyncSnapshot<String> text) {
print(text);
if(text== "-1"){
return CircularProgressIndicator();
} else {
return Column(
children: <Widget>[
ListTile(
subtitle: Text('Admin View', textAlign: TextAlign.center,
style: TextStyle(fontSize: 29.0,
color: Colors.indigo,
fontWeight: FontWeight.bold),),
),
Expanded(child: GridView(
gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
crossAxisCount: 2,),
children: <Widget>[
Padding(
padding: const EdgeInsets.all(18.0), child: Card(
child: ListTile(title: FlatButton.icon(
onPressed: null,
icon: Icon(
Icons.directions_boat, color: Colors.black,),
label: Text("Boats", style: TextStyle(
fontSize: 9, color: Colors.indigo),)),
subtitle: Text('3', textAlign: TextAlign.center,
style: TextStyle(
color: active, fontSize: 50.0),)),
),
),
Padding(padding: const EdgeInsets.all(18.0),
child: Card(child: ListTile(
title: FlatButton.icon(
onPressed: null,
icon: Icon(
Icons.people, color: Colors.black,),
label: Text("Users", style: TextStyle(
fontSize: 9, color: Colors.indigo),)),
subtitle: Text(text.data != null ? text.data : '',
textAlign: TextAlign.center,
style: TextStyle(color: active, fontSize: 50.0),
)),
),
),
Padding(
padding: const EdgeInsets.all(22.0),
child: Card(
child: ListTile(
title: FlatButton.icon(
onPressed: null,
icon: Icon(
Icons.bookmark, color: Colors.black,),
label: Text("Bookings", style: TextStyle(
fontSize: 8, color: Colors.indigo),)),
subtitle: Text(
'120',
textAlign: TextAlign.center,
style: TextStyle(
color: active, fontSize: 50.0),
)),
),
),
],
),
),
],
);
} })
我返回的是空字符串值，但是当包含这组行Text(text.data ??'default value')时，我可以清除该错误，但仍然无法清除我的问题，请有人帮助我
最佳答案
您需要在从Firestore获取数据之前添加 await ，因为它是异步的，并且您不等待结果并返回已初始化为0的值
Future<String> getUsersCount() async {
var length = 0;
await Firestore.instance.collection('users').getDocuments().then((myDocuments){
print("${myDocuments.documents.length}");
length = myDocuments.documents.length;
});
return Future.value(length.toString());
}
如您所见，用户的值count(36)正在打印，但不会返回，因为在异步执行完成之前调用了return。
关于firebase - 返回Firebase Flutter中的集合数时出错？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/59291240/