text
stringlengths 1
372
|
---|
),
|
);
|
}
|
}
|
class SignaturePainter extends CustomPainter {
|
SignaturePainter(this.points);
|
final List<Offset?> points;
|
@override
|
void paint(Canvas canvas, size size) {
|
final paint paint = paint()
|
..color = colors.black
|
..strokeCap = StrokeCap.round
|
..strokeWidth = 5;
|
for (int i = 0; i < points.length - 1; i++) {
|
if (points[i] != null && points[i + 1] != null) {
|
canvas.drawLine(points[i]!, points[i + 1]!, paint);
|
}
|
}
|
}
|
@override
|
bool shouldRepaint(SignaturePainter oldDelegate) =>
|
oldDelegate.points != points;
|
}
|
<code_end>
|
<topic_end>
|
<topic_start>
|
widget opacity
|
in UIKit, everything has .opacity or .alpha.
|
in flutter, most of the time you need to
|
wrap a widget in an opacity widget to accomplish this.
|
<topic_end>
|
<topic_start>
|
custom widgets
|
in UIKit, you typically subclass UIView, or use a pre-existing view,
|
to override and implement methods that achieve the desired behavior.
|
in flutter, build a custom widget by composing smaller widgets
|
(instead of extending them).
|
for example, how do you build a CustomButton
|
that takes a label in the constructor?
|
create a CustomButton that composes a ElevatedButton with a label,
|
rather than by extending ElevatedButton:
|
<code_start>
|
class CustomButton extends StatelessWidget {
|
const CustomButton(this.label, {super.key});
|
final string label;
|
@override
|
widget build(BuildContext context) {
|
return ElevatedButton(
|
onPressed: () {},
|
child: text(label),
|
);
|
}
|
}
|
<code_end>
|
then use CustomButton,
|
just as you’d use any other flutter widget:
|
<code_start>
|
@override
|
widget build(BuildContext context) {
|
return const center(
|
child: CustomButton('Hello'),
|
);
|
}
|
<code_end>
|
<topic_end>
|
<topic_start>
|
navigation
|
this section of the document discusses navigation
|
between pages of an app, the push and pop mechanism, and more.
|
<topic_end>
|
<topic_start>
|
navigating between pages
|
in UIKit, to travel between view controllers, you can use a
|
UINavigationController that manages the stack of view controllers
|
to display.
|
flutter has a similar implementation,
|
using a navigator and routes.
|
a route is an abstraction for a “screen” or “page” of an app,
|
and a navigator is a widget
|
that manages routes. a route roughly maps to a
|
UIViewController. the navigator works in a similar way to the iOS
|
UINavigationController, in that it can push() and pop()
|
routes depending on whether you want to navigate to, or back from, a view.
|
to navigate between pages, you have a couple options:
|
the following example builds a map.
|
<code_start>
|
void main() {
|
runApp(
|
CupertinoApp(
|
home: const MyAppHome(), // becomes the route named '/'
|
routes: <string, WidgetBuilder>{
|
'/a': (context) => const MyPage(title: 'page a'),
|
'/b': (context) => const MyPage(title: 'page b'),
|
'/c': (context) => const MyPage(title: 'page c'),
|
},
|
),
|
);
|
}
|
<code_end>
|
navigate to a route by pushing its name to the navigator.
|
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