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windows doesn’t support file name wildcarding.
instead, list the .arb files that were generated by the
intl_translation:extract_to_arb command.
the DemoLocalizations class uses the generated
initializeMessages() function
(defined in intl_messages_all.dart)
to load the localized messages and intl.message()
to look them up.
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more information
if you learn best by reading code,
check out the following examples.
if dart’s intl package is new to you,
check out using the dart intl tools.
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state management
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topics
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state management
info note
if you have written a mobile app using flutter
and wonder why your app’s state is lost
on a restart, check out restore state on android
or restore state on iOS.
if you are already familiar with state management in reactive apps,
you can skip this section, though you might want to review the
list of different approaches.
as you explore flutter,
there comes a time when you need to share application
state between screens, across your app.
there are many approaches you can take,
and many questions to think about.
in the following pages,
you will learn the basics of dealing with state in flutter apps.
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start thinking declaratively
if you’re coming to flutter from an imperative framework
(such as android SDK or iOS UIKit), you need to start
thinking about app development from a new perspective.
many assumptions that you might have don’t apply to flutter. for example, in
flutter it’s okay to rebuild parts of your UI from scratch instead of modifying
it. flutter is fast enough to do that, even on every frame if needed.
flutter is declarative. this means that flutter builds its user interface to
reflect the current state of your app:
when the state of your app changes
(for example, the user flips a switch in the settings screen),
you change the state, and that triggers a redraw of the user interface.
there is no imperative changing of the UI itself
(like widget.setText)—you change the state,
and the UI rebuilds from scratch.
read more about the declarative approach to UI programming
in the get started guide.
the declarative style of UI programming has many benefits.
remarkably, there is only one code path for any state of the UI.
you describe what the UI should look
like for any given state, once—and that is it.
at first,
this style of programming might not seem as intuitive as the
imperative style. this is why this section is here. read on.
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differentiate between ephemeral state and app state
this doc introduces app state, ephemeral state,
and how you might manage each in a flutter app.
in the broadest possible sense, the state of an app is everything that
exists in memory when the app is running. this includes the app’s assets,
all the variables that the flutter framework keeps about the UI,
animation state, textures, fonts, and so on. while this broadest
possible definition of state is valid, it’s not very useful for
architecting an app.
first, you don’t even manage some state (like textures).
the framework handles those for you. so a more useful definition of
state is “whatever data you need in order to rebuild your UI at any
moment in time”. second, the state that you do manage yourself can
be separated into two conceptual types: ephemeral state and app state.
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ephemeral state
ephemeral state (sometimes called UI state or local state)
is the state you can neatly contain in a single widget.
this is, intentionally, a vague definition, so here are a few examples.
other parts of the widget tree seldom need to access this kind of state.
there is no need to serialize it, and it doesn’t change in complex ways.
in other words, there is no need to use state management techniques
(scopedmodel, redux, etc.) on this kind of state.
all you need is a StatefulWidget.
below, you see how the currently selected item in a bottom navigation bar is
held in the _index field of the _MyHomepageState class.
in this example, _index is ephemeral state.
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class MyHomepage extends StatefulWidget {
const MyHomepage({super.key});
@override
State<MyHomepage> createState() => _MyHomepageState();