Flutter 如何刷新 StreamBuilder? [英] Flutter How to refresh StreamBuilder?
问题描述
考虑以下代码:
StreamBuilder<QuerySnapshot> _createDataStream(){
return StreamBuilder<QuerySnapshot>(
stream: Firestore.instance.collection("data").limit.(_myLimit).snapshots(),
builder: (context, snapshot){
return Text(_myLimit.toString);
}
);
}
我希望 StreamBuilder 在 _myLimit
变量更改时刷新.可以这样做:
I want that the StreamBuilder refreshes when the _myLimit
Variable changes.
It's possible doing it like this:
void _incrementLimit(){
setState(() =>_myLimit++);
}
我的问题是,除了 setState((){});
之外,是否还有另一种更快的方法.因为当 _myLimit
变量发生变化时,我不想回忆整个 build()
方法.
My Question is if there is another, faster way, except the setState((){});
one.
Because I don't want to recall the whole build()
method when the _myLimit
Variable changes.
我想出了另一种方式,但我觉得有一个更好的解决方案,因为我认为我没有使用 .periodic
功能,而且我得到了一个嵌套的 Stream 我不确定这是多么平常:
I figured out another Way but I feel like there is a even better solution because I think I don't make use of the .periodic
functionality and I got a nested Stream I'm not sure how usual this is:
Stream<int> myStream = Stream.periodic(Duration(), (_) => _myLimit);
...
@override
Widget build(BuildContext context){
...
return StreamBuilder<int>(
stream: myStream,
builder: (context, snapshot){
return _createDataStream;
},
),
...
}
<小时>
解决方案
import 'dart:async';
import 'package:flutter/material.dart';
void main() => runApp(new MyApp());
class MyApp extends StatefulWidget {
@override
State<StatefulWidget> createState() {
return new _MyAppState();
}
}
class _MyAppState extends State<MyApp> {
int myNum = 0;
final StreamController _myStreamCtrl = StreamController.broadcast();
Stream get onVariableChanged => _myStreamCtrl.stream;
void updateMyUI() => _myStreamCtrl.sink.add(myNum);
@override
void initState() {
super.initState();
}
@override
void dispose() {
_myStreamCtrl.close();
super.dispose();
}
@override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
body: Center(
child:
Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
StreamBuilder(
stream: onVariableChanged,
builder: (context, snapshot){
if(snapshot.connectionState == ConnectionState.waiting){
updateMyUI();
return Text(". . .");
}
return Text(snapshot.data.toString());
},
),
RaisedButton(
child: Text("Increment"),
onPressed: (){
myNum++;
updateMyUI();
},
)
],
),
)));
}
}
其他一些想法,StreamBuilder 的外观如何:
Some other ideas, how the StreamBuilder also could look like:
StreamBuilder(
stream: onVariableChanged,
builder: (context, snapshot){
if(snapshot.connectionState == ConnectionState.waiting){
return Text(myNum.toString());
}
return Text(snapshot.data.toString());
},
),
StreamBuilder(
stream: onVariableChanged,
initialData: myNum,
builder: (BuildContext context, AsyncSnapshot snapshot){
if(snapshot.data == null){
return Text("...");
}
return Text(snapshot.data.toString());
},
),
推荐答案
使用 broadcast
声明一个 StreamController
,然后为 Stream
设置一个友好名称这个 StreamController
的代码>,然后每次你想重建包装的小部件(StreamBuilder
的孩子只需使用 sink
属性code>StreamController 到 add
一个将触发 StreamBuilder
的新值.
Declare a StreamController
with broadcast
, then set a friendly name to the Stream
of this StreamController
, then everytime you want to rebuild the wraped widget (the child of the StreamBuilder
just use the sink
property of the StreamController
to add
a new value that will trigger the StreamBuilder
.
您可以使用 StreamBuilder
和 AsyncSnapshot
而无需设置类型.
You can use StreamBuilder
and AsyncSnapshot
without setting the type.
但是如果您在键入 snapshot.data.
时使用 StreamBuilder
和 AsyncSnapshot
,您将看到所有变量和UserModel
中的方法.
But if you use StreamBuilder<UserModel>
and AsyncSnapshot<UserModel>
when you type snapshot.data.
you will see all variables and methods from the UserModel
.
final StreamController<UserModel> _currentUserStreamCtrl = StreamController<UserModel>.broadcast();
Stream<UserModel> get onCurrentUserChanged => _currentUserStreamCtrl.stream;
void updateCurrentUserUI() => _currentUserStreamCtrl.sink.add(_currentUser);
StreamBuilder<UserModel>(
stream: onCurrentUserChanged,
builder: (BuildContext context, AsyncSnapshot<UserModel> snapshot) {
if (snapshot.data != null) {
print('build signed screen, logged as: ' + snapshot.data.displayName);
return blocs.pageView.pagesView; //pageView containing signed page
}
print('build login screen');
return LoginPage();
//print('loading');
//return Center(child: CircularProgressIndicator());
},
)
通过这种方式,您可以使用 StatelessWidget
并刷新单个子小部件
(例如具有不同颜色的图标)而无需使用 setState
(重建整个页面).
This way you can use a StatelessWidget
and refresh just a single sub-widget
(an icon with a different color, for example) without using setState
(that rebuilds the entire page).
对于性能,流是最好的方法.
For performance, streams are the best approach.
我正在使用 BLoC 架构
方法,因此最好在 homePageBloc.dart(具有包含所有业务逻辑的普通控制器类)中声明变量并在 homePage.dart 中创建 StreamBuilder(具有扩展无状态/有状态小部件并负责 UI 的类).
I'm using BLoC architecture
approach, so it's much better to declare the variables in a homePageBloc.dart (that has a normal controller class with all business logic) and create the StreamBuilder in the homePage.dart (that has a class that extends Stateless/Stateful widget and is responsible for the UI).
我的UserModel.dart
,你可以用DocumentSnapshot
代替Map
如果您使用的是 Firebase 中的 Cloud Firestore 数据库.
My UserModel.dart
, you can use DocumentSnapshot
instead of Map<String, dynamic>
if you are using Cloud Firestore database from Firebase.
class UserModel {
/// Document ID of the user on database
String _firebaseId = "";
String get firebaseId => _firebaseId;
set firebaseId(newValue) => _firebaseId = newValue;
DateTime _creationDate = DateTime.now();
DateTime get creationDate => _creationDate;
DateTime _lastUpdate = DateTime.now();
DateTime get lastUpdate => _lastUpdate;
String _displayName = "";
String get displayName => _displayName;
set displayName(newValue) => _displayName = newValue;
String _username = "";
String get username => _username;
set username(newValue) => _username = newValue;
String _photoUrl = "";
String get photoUrl => _photoUrl;
set photoUrl(newValue) => _photoUrl = newValue;
String _phoneNumber = "";
String get phoneNumber => _phoneNumber;
set phoneNumber(newValue) => _phoneNumber = newValue;
String _email = "";
String get email => _email;
set email(newValue) => _email = newValue;
String _address = "";
String get address => _address;
set address(newValue) => _address = newValue;
bool _isAdmin = false;
bool get isAdmin => _isAdmin;
set isAdmin(newValue) => _isAdmin = newValue;
/// Used on first login
UserModel.fromFirstLogin() {
_creationDate = DateTime.now();
_lastUpdate = DateTime.now();
_username = "";
_address = "";
_isAdmin = false;
}
/// Used on any login that isn't the first
UserModel.fromDocument(Map<String, String> userDoc) {
_firebaseId = userDoc['firebaseId'] ?? '';
_displayName = userDoc['displayName'] ?? '';
_photoUrl = userDoc['photoUrl'] ?? '';
_phoneNumber = userDoc['phoneNumber'] ?? '';
_email = userDoc['email'] ?? '';
_address = userDoc['address'] ?? '';
_isAdmin = userDoc['isAdmin'] ?? false;
_username = userDoc['username'] ?? '';
//_lastUpdate = userDoc['lastUpdate'] != null ? userDoc['lastUpdate'].toDate() : DateTime.now();
//_creationDate = userDoc['creationDate'] != null ? userDoc['creationDate'].toDate() : DateTime.now();
}
void showOnConsole(String header) {
print('''
$header
currentUser.firebaseId: $_firebaseId
currentUser.username: $_username
currentUser.displayName: $_displayName
currentUser.phoneNumber: $_phoneNumber
currentUser.email: $_email
currentUser.address: $_address
currentUser.isAdmin: $_isAdmin
'''
);
}
String toReadableString() {
return
"displayName: $_displayName; "
"firebaseId: $_firebaseId; "
"email: $_email; "
"address: $_address; "
"photoUrl: $_photoUrl; "
"phoneNumber: $_phoneNumber; "
"isAdmin: $_isAdmin; ";
}
}
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