如何在Dart中的流构建器中切换正在收听的流? [英] How can i switch the stream I am listening to in a streambuilder in Dart?
问题描述
基本上，当页面第一次加载时，我想使用1个按地理位置查询的流，但是要检查变量socialVisible为true的文档，然后当用户单击按钮进行切换时，我希望该流仍然通过以下方式查询地理位置，但现在使用profVisible字段检查文档.
Basically when the page first loads i want to use 1 stream that queries by geolocation but checks for documents where variable socialVisible is true, and then when the user clicks on a button to switch, i want the stream to instead still query by geolocation but now checks the documents with the field profVisible.
从理论上讲，这非常简单，每当按下相应的按钮时，我都会设置状态，以使socialPressed = true和profPressed = false，然后在streambuilder中，我使用三元运算符根据真实值来决定应使用哪个流of socialPressed和profPressed.
In theory this is very simple, whenever the corresponding button is pressed i set the state so that socialPressed=true and profPressed=false and then inside the streambuilder i used ternary operators to decide which stream should be used based on the truth values of socialPressed and profPressed.
但是，这仅在第一次单击时有效，socialPressed的初始值为true，因此初始流为社交流，然后当我单击以转到教授时，它将成功切换流.但是，在这段时间之后，当我尝试返回社交网站时，教授的所有文档都保留了，而不是被社交网站所取代?即使我将初始流切换为教授，也会发生这种情况，而且我不明白为什么会发生这种情况?
However, this only works on the first click, the initial value of socialPressed is true so the initial stream is the social one and then when i click to go to the prof one it switches streams successfully. However after this time when i try to go back to social all the documents from prof remain instead of being replaced by social? This happens even when i switched the initial stream to prof, and i do not understand why this is happening?
StreamBuilder(
stream:socialPressed==true?socStream:proStream,
builder:
(context, AsyncSnapshot<List<DocumentSnapshot>> snapshots) {
if (!snapshots.hasData) {
return Container(
alignment: FractionalOffset.center,
child: CircularProgressIndicator());
} else {
return Container(
child: Container(
child: (snapshots.data.length == 0)
Container(
height: MediaQuery.of(context).size.height * 2 / 3,
child: ListView.builder(
itemBuilder: (context, index) {
DocumentSnapshot doc = snapshots.data[index];
return UserTile('this is where i use the doc data')},
itemCount: snapshots.data.length,
),),));}},)
这是我代码的基本结构，我删除了不相关的信息.
This is the basic structure of my code, i have removed irrelevant info.
请求了按钮回调代码:
FloatingActionButton(
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.all(Radius.circular(16.0))),
onPressed: () {
setState(() {
likeType='social';
socialPressed=!socialPressed;
});
},
elevation: 0,
heroTag: 'socialButton',
backgroundColor: socialPressed==false?Colors.grey[100]:Color(0xFFe0bdff),
child: Icon(
Entypo.drink,
color: Color(0xFF8803fc),
),
),
FloatingActionButton(
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.all(Radius.circular(16.0))),
onPressed: () {
setState(() {
likeType='prof';
socialPressed=!socialPressed;
});
},
elevation: 0,
heroTag: 'profButton',
backgroundColor: socialPressed==true?Colors.grey[100]:Color(0xFFb9ebe9),
child: Row(
children: <Widget>[
SizedBox(
width: MediaQuery.of(context).size.width / 30,
),
Icon(
FontAwesome.graduation_cap,
color: Color(0xFF096664),
),
],
),
),
推荐答案
我也遇到了这个问题.我正在使用RX Dart，并尝试根据布尔变量切换流.
I too faced this issue. I am using RX Dart and tried to switch streams based on a boolean variable.
我最初是在流中使用PublishSubject.切换到行为主体"已为我解决了该问题.目前，我尚不足以了解其工作原理，但会尝试对其进行进一步探索，并在可能的情况下在此处进行编辑.
I was initially using PublishSubject for my stream. Switching to Behaviour Subject solved the issue for me. At this moment I don't have sufficient knowledge on why this works but would try to explore it further and edit here if possible.
先前的代码:
final _activeOrdersFetcher = PublishSubject<OrderListModel>();
final _completedOrdersFetcher = PublishSubject<OrderListModel>();
StreamBuilder<OrderListModel>(
stream: isActive
? _ordersBloc.getActiveOrders
: _ordersBloc.getCompletedOrders
新代码更改:
final _activeOrdersFetcher = BehaviorSubject<OrderListModel>();
final _completedOrdersFetcher = BehaviorSubject<OrderListModel>();
这篇关于如何在Dart中的流构建器中切换正在收听的流?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
