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a constraint becomes tight when its constraint’s minimum size value
equals its maximum size value.
in SwiftUI, views might expand to the available space or
limit their size to that of its content.
flutter widgets behave in similar manner.
however, in flutter parent widgets can offer unbounded constraints.
unbounded constraints set their maximum values to infinity.
if the child expands and it has unbounded constraints,
flutter returns an overflow warning:
to learn how constraints work in flutter,
see understanding constraints.
<topic_end>
<topic_start>
design system
because flutter targets multiple platforms, your app doesn’t need
to conform to any design system.
though this guide features material widgets,
your flutter app can use many different design systems:
if you’re looking for a great reference app that features a
custom design system, check out wonderous.
<topic_end>
<topic_start>
UI basics
this section covers the basics of UI development in
flutter and how it compares to SwiftUI.
this includes how to start developing your app, display static text,
create buttons, react to on-press events, display lists, grids, and more.
<topic_end>
<topic_start>
getting started
in SwiftUI, you use app to start your app.
another common SwiftUI practice places the app body within a struct
that conforms to the view protocol as follows:
to start your flutter app, pass in an instance of your app to
the runApp function.
<code_start>
void main() {
runApp(const MyApp());
}
<code_end>
app is a widget. the build method describes the part of the
user interface it represents.
it’s common to begin your app with a WidgetApp class,
like CupertinoApp.
<code_start>
class MyApp extends StatelessWidget {
const MyApp({super.key});
@override
widget build(BuildContext context) {
// returns a CupertinoApp that, by default,
// has the look and feel of an iOS app.
return const CupertinoApp(
home: HomePage(),
);
}
}
<code_end>
the widget used in HomePage might begin with the scaffold class.
scaffold implements a basic layout structure for an app.
<code_start>
class HomePage extends StatelessWidget {
const HomePage({super.key});
@override
widget build(BuildContext context) {
return const scaffold(
body: center(
child: text(
'hello, world!',
),
),
);
}
}
<code_end>
note how flutter uses the center widget.
SwiftUI renders a view’s contents in its center by default.
that’s not always the case with flutter.
scaffold doesn’t render its body widget at the center of the screen.
to center the text, wrap it in a center widget.
to learn about different widgets and their default behaviors, check out
the widget catalog.
<topic_end>
<topic_start>
adding buttons
in SwiftUI, you use the button struct to create a button.
to achieve the same result in flutter,
use the CupertinoButton class:
<code_start>
CupertinoButton(
onPressed: () {
// this closure is called when your button is tapped.
},
child: const Text('Do something'),
)
<code_end>
flutter gives you access to a variety of buttons with predefined styles.
the CupertinoButton class comes from the cupertino library.
widgets in the cupertino library use apple’s design system.
<topic_end>
<topic_start>