I have 4 widgets named OptionCard (it's their Type) i'de like to iterate through them to check the value of their variables how can I do it ?
tried OptionCard.forEach but it doesn't work
This is not the way Flutter widgets are supposed to be used. Widgets (even StatefulWidgets) generally do not hold application state. They should only provide a view on state managed elsewhere.
There are many proven methods of application state management that are popular and well supported in Flutter.
Related
When creating a Flutter application,
we use a Navigator to move back and forth between screens.
In my application, I have some class instances that
I want to share with all child widgets in the hierarchy.
An example is a Data Base driver class (stateful)
which holds all functionality of reading/writing to the actual database.
Currently - the 'main' function is initializing it,
then the resulting object is passed through all
constructors of the participating widgets.
How do I make it behave like the Navigator
so it would be available in the global scope
without importing it or passing it through a chain of constructors?
I would gladly accept any other approaches,
and still, if you can also address the exact question - I would be grateful :)
I opened the code of Navigator, Stateless and Stateful widgets,
I tried to google for the source of that Navigator instance
but came up with nothing helpful.
Have you tried using InheritedWidget?
From the docs:
Base class for widgets that efficiently propagate information down the tree.
Create DataBaseDriver class as inherited Widget class, access it in its child class using context as DataBaseDriver.of(context)
I have a flutter application which uses a MultiProvider widget at the root of the widgets tree.
The problem is, I need to add a ChangeNotifierProvider to the MultiProvider widget, but later because I can't create it at the beginning (well I could but it makes more sense to do it later *).
How am I supposed to do?
(* for more details about why I would like to create the ChangeNotifierProvider later: The associated ChangeNotifier represents a bluetooth connection that will not be available at the start of the application.)
In these situations I create Provider with object which have some initial values and later I change initial values to actual.
I'm writing a Flutter app and planning to use GetX for state management (amongst other things). The common design pattern seems to be to use one dart file per view (screen) and for each view to have its own associated controller file.
However, what is the best approach when you have state that isn't just used within a single screen, but instead needs to be shared across screens? It seems wrong to import controllers from one view into the view or controller for another screen. Is there a better way?
Thanks
You can use GetxService: https://pub.flutter-io.cn/documentation/get_state_manager/latest/get_state_manager/GetxService-class.html
As it says: Unlike GetxController, which serves to control events on each of its pages, GetxService is not automatically disposed (nor can be removed with Get.delete()). It is ideal for situations where, once started, that service will remain in memory, such as Auth control for example. Only way to remove it is Get.reset().
I'm building my first Flutter app, in which I need to refresh a list of data, and every component has some modifiers.
This is the basic architecture.
A big list of data (about 5000 rows) is periodically refreshed from an API inside a RefresherWidget (which is a StatefulWidget that holds the list), and then passed along to the children.
Every RowWidget has a Switch (and Dialogs too) that modifies the data it represents.
Currently, the methods to modify the list are in the RefresherWidget, so I'm passing them as callback functions inside every children until reaching the onChanged callback of the Switch.
But I don't think it's a very clean solution, and I don't know how to implement a better one: I've tried thinking about passing these methods inside an InheritedWidget that stays between RefresherWidget and ListViewWidget, and referencing them using the of function, but I don't know about the perfomance hit I would get if the InheritedWidget gets rebuild.
Also, Streams and BLoCs seem very complicated for what I need to do.
How do you guys usually approach a problem like this?
This is definitely a situation for InheritedWidget or BuildContext in general.
I've tried [...] InheritedWidget [...] but I don't know about the perfomance hit I would get if the InheritedWidget gets rebuild.
You don't have to fear anything. InheritedWidget is built for this exact purpose.
Obtaining the InheritedWidget is very performant (O(1)). And only widgets that depends on the value gets rebuilt – which is optimal too.
Web view takes more than 4 sec to load the webpage. The same page takes less than 2 sec in Native app. Is there a way to speedup the load time. I tried both Official webview_flutter and flutter_webview_plugin.
If you app relies on WebView, just choose other tools: Swift for iOS & Kotlin for Android.
Here is why:
WebView actually does not load pages slow. Instead, creating the WebView widget is slow;
In order to solve 1, you might want use a cached WebView. Unfortunately, that is not easy. Layout changes (e.g. animation) might trigger a WebView "recreating" (the cached WebView becomes invalid/staled). And the "recreating" is very slow;
Flutter's widgets depend on "state" outside of the widgets, and widgets' creating are supposed to be fast/simple. Unfortunately, WebView (which is not a native widget) is not the case. WebView has its complex internal "state", a recreation simple discard everything and you returns to the WebView's initial state (initial URL). And it is very slow (Creating time + LoadTime: Network overhead);
It is very hard to create a "external state" outside a WebView, therefore after a WebView's recreating it cannot resume from the external state;
Since WebView's recreating is very slow, it totally kills animation and gives user a very bad experience. A solution might be put a WebView as your main page and never try to animate to a new WebView (just like a Wiki App Demo in YouTube).
Conclusion:
So, now, WebView in flutter is not ready and please don't consider use it seriously.
Discussion:
Flutter's widgets design is quite "unusual" since they are basically immutable. States outside widgets (external state) are used. When state changes, instead of modify the widget, Flutter choose to create a new widget based on the new state. Therefore, widgets are deigned to be light weighted so they can be created/destroyed very quickly. Unfortunately, WebView cannot fall into this category. WebView is as complex as the whole Flutter framework, so it cannot be a native widget but a plug-in. And WebView has its own internal state which is not compatible with the framework, which results in keep on being destroyed/recreated by the framework.
I am not sure why Flutter's widgets are designed in this way, maybe it is easier/faster for creating the framework? I saw some complex examples (~100 lines) using Redux/BLOC/Steam just in order to "change" a widget, which might just need a one-line of code in other frameworks.
Performance is also an issue. Rebuild a complex widgets tree is slow. Then you need writing a lot of code (Redux/BLOC/Stream/ScoppedModel...) in order to implement a partial widgets tree build.
Even for a very simple app, performance of Flutter is still not as good as native (https://thoughtbot.com/blog/examining-performance-differences-between-native-flutter-and-react-native-mobile-development). In fact, I'd like considering Flutter as "native" since it is compiled into machine code instead of Java's ByteCode.
Finally:
I am a new Flutter learner and start playing with Flutter for a couple of weeks. The widgets framework and the WebView plug-in just made me headache. A lot of time spent on the UI interface instead of the core logic of my app.
I am not saying Flutter is not good. Actually, I think it is the best cross-platform framework for iOS/Android. It just might be something (e.g. complex external widget like WebView) was not being taken into consideration while the framework was being designed. Hope the Flutter team can find a solution for this, maybe a special case for handling a complex external plug-in?
I will keep on learning/playing with Flutter.
And now Hybrid-Composition is default in webview_flutter 3.0.0:
https://pub.dev/packages/webview_flutter/changelog
Just tried it on my side and since it's not perfect, it's much more faster
cheers!
Updated to webview_flutter 1.0.x and adopted Hybrid-Composition. It performances much better on Android now.
Announcement: announcing-flutter-1-22-44f146009e5f
How to: webview_flutter
Docs: Hybrid-Composition