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@override |
Widget build(BuildContext context) => const Scaffold(body: Signature()); |
} |
class Signature extends StatefulWidget { |
const Signature({super.key}); |
@override |
SignatureState createState() => SignatureState(); |
} |
class SignatureState extends State<Signature> { |
List<Offset?> _points = <Offset>[]; |
@override |
Widget build(BuildContext context) { |
return GestureDetector( |
onPanUpdate: (details) { |
setState(() { |
RenderBox? referenceBox = context.findRenderObject() as RenderBox; |
Offset localPosition = |
referenceBox.globalToLocal(details.globalPosition); |
_points = List.from(_points)..add(localPosition); |
}); |
}, |
onPanEnd: (details) => _points.add(null), |
child: CustomPaint( |
painter: SignaturePainter(_points), |
size: Size.infinite, |
), |
); |
} |
} |
class SignaturePainter extends CustomPainter { |
SignaturePainter(this.points); |
final List<Offset?> points; |
@override |
void paint(Canvas canvas, Size size) { |
var 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> |
How do I build custom widgets? |
In Android, you typically subclass View, 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). |
It is somewhat similar to implementing a custom ViewGroup |
in Android, where all the building blocks are already existing, |
but you provide a different behavior—for example, |
custom layout logic.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 { |
final String label; |
const CustomButton(this.label, {super.key}); |
@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> |
Intents |
<topic_end> |
<topic_start> |
What is the equivalent of an Intent in Flutter? |
In Android, there are two main use cases for Intents: navigating between |
Activities, and communicating with components. Flutter, on the other hand, |
does not have the concept of intents, although you can still start intents |
through native integrations (using a plugin).Flutter doesn’t really have a direct equivalent to activities and fragments; |
rather, in Flutter you navigate between screens, using a Navigator and |
Routes, all within the same Activity.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 an |
Activity, but it does not carry the same meaning. A navigator can push |
and pop routes to move from screen to screen. Navigators work like a stack |
on which you can push() new routes you want to navigate to, and from |
which you can pop() routes when you want to “go back”.In Android, you declare your activities inside the app’s AndroidManifest.xml.In Flutter, you have a couple options to navigate between pages:The following example builds a Map. |
<code_start>void main() { |
runApp(MaterialApp( |
home: const MyAppHome(), // Becomes the route named '/'. |
routes: <String, WidgetBuilder>{ |
'/a': (context) => const MyPage(title: 'page A'), |