i am working on flutter project Apply Getx and MVC Arcitecture but when i am getting stream from firestore first it got null values but when hot reload on that page values will goes in to place how to remove this Error, Almost in All type of modules I have to face this Error.
I am trying init State but Ui build first than function in Init State.
It is quite normal for StreamBuilders or FutureBuilders to call their builder function with null values.
The reason is that the build function may be called at any time, irrespective of the stream or future's state.
You should use the hasData property of the snapshot to check for valid data, and handle the case of null data, e.g. by returning a SizedBox widget.
StreamBuilder(
stream: yourStream,
builder: (context, snapshot) {
if (snapshot.hasData) {
return yourWidget();
} else {
return const SizedBox();
}
},
);
Related
I'm trying get a callback after my context build, i already tried with "WidgetsBinding.instance!.addPostFrameCallback", but not works because i have a StreamBuilder and the first load of snapshot data it is null.
I expected exists a callback of StreamBuilder after data completely load and build loaded, here is my code:
StreamBuilder(
stream: this.paymentInfoFormPresenter.key,
builder: (context, snapshot) {
final _formKey = snapshot.data;
if (_formKey == null) {
return Container();
}
return Text('example');
}
);
And i don't find anything about on internet... i hope someone can help me.
To resolve this issue, i needed change the "Text('example')" to an external widget, and added "WidgetsBinding.instance!.addPostFrameCallback" inside of this external widget
a Flutter beginner here so if my question is stupid don't mind it...
How can I convert a Stream to a Future?
I have a Stream that just calls the requested URL multiple times because it's a Stream. I want to be able to get the data and not the loading state... Because I always just get loading forever
Is there something like Future.fromStream() function somewhere and I'm missing it?
Can I achieve this?
I didn't provide any code because I think it's not needed if you need the code, I can edit the question
Stream has firstWhere method, this will return Future
_profileService.profileStream.firstWhere((element) => false);
Stream and Future are two different concepts.
As you are using, stream is keeping the data updated, and Future is just one time.
Example of using stream: Shopping Cart, listing of items
Example of using future: getUserDetails after login.
If you're using stream, then you can use streambuilder to build your UI
StreamBuilder<User>(
stream: userBloc.author, // your stream here
builder:
(BuildContext context, AsyncSnapshot<User> snapshot) {
if (snapshot.connectionState == ConnectionState.active && snapshot.hasData) {
// do your work here
} else {
return CircularprogressIndicator();
}
},
)
I am using FutureBuilder inside my Build method and the FutureBuilder keeps firing up again and again. I only want to call FutureBuilder once until my future is loaded and then call another function as soon as it is done. This is my Build function -
#override
Widget build(BuildContext context) {
return FutureBuilder(
future: parsings(),
builder:
(BuildContext context, AsyncSnapshot<dynamic> snapshot) {
switch (snapshot.connectionState) {
case ConnectionState.waiting:
return LoadingState(context);
default:
if (snapshot.hasError)
return new Text(
'Error in snapshot: \n${snapshot.error}');
else {
return func1();
}
}
},
);
}
As i said, my Build function keeps on building again and again.
Before this, i was using my future inside initState but because of that, my actual page that i wanted to return gave null values all over until the API was called. I dont want to see null values at all so i wanted to use FutureBuilder and display LoadingState() until the API was called and then show my page which has all the called values and doesnt show null values. Any help would be appreciated.
EDIT: The detailed issue i am facing is as the build function is being called again and again, i am seeing my LoadingState() again and again, that is, LoadingState() is appearing and then func1() is appearing then again, LoadingState(), then func1() and so on. this process does not stop at all. Also, i do not want to use parsings() in initState because on doing so, before the API is called, the func1() shows null values in my data and as soon as it is called, the build function changes its values to the values called from API. I don't want to see it like that which is why i wanted to use FutureBuilder.
I'm currently working on an app and I want to get some data of a user's friends. Ideally, after sign in, this information is loaded up onto the screen for viewing.
I initially made my function call to do this within the "build" method of my HomeScreen, but this caused an infinite loop as the function call ended with "notifyListeners()".
That being said, where should I place my call to avoid a loop, while still having the UI update once the data has been fetched from the database?
You should have a look at the FutureBuilder widget, which provides great functionality to load async data and show the result once available. While the data is loading, or if your code runs into an error, you can show a different widget. Essentially it works like this:
FutureBuilder<String>(
future: _yourFuture,
builder: (context, snapshot) {
switch (snapshot.connectionState) {
case ConnectionState.active:
case ConnectionState.waiting:
// Return loading indicator
return Container();
case ConnectionState.done:
if (snapshot.hasError) {
// Return error
return Container();
} else if (snapshot.hasData) {
// Data loaded => use snapshot.data to access it
return Container();
}
}
})
I would not recommend to load data during initState(), since this method cannot be async and thus, you cannot await your result.
I hope that helps.
I want to populate my lists by making API calls when moving to a screen in flutter. I tried calling the async function in the init state however it takes time to load the data of course, and that leads to a null error.
I tried using a future builder in my view. However, I want to make multiple API calls and I don't think that is possible with one future builder. And I would like to avoid having different future builders for each list.
Is there a neat way to do this?
Also is it advisable to load data and pass it on from the previous screen.. since I would like to avoid the loading time?
current code
FutureBuilder(
future: getAllData,
initialData: [],
builder: (context, snapshot) {
if (!snapshot.hasData || snapshot.data.isEmpty) return Center(child: CircularProgressIndicator(valueColor: new AlwaysStoppedAnimation<Color>(Colors.red),));
else {
return createNewTaskView(context, snapshot.data);
}
}),
init method
#override
void initState() {
this.getAllData = getSocieties();
}