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Flutter_Documentation

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size if needed.In Flutter, use the Image.network constructor to include
an image from a URL.
<code_start>Image.network('https://docs.flutter.dev/assets/images/docs/owl.jpg');<code_end>
<topic_end>
<topic_start>
How do I install packages and package plugins?
Flutter supports using shared packages contributed by other developers to the
Flutter and Dart ecosystems. This allows you to quickly build your app without
having to develop everything from scratch. Packages that contain
platform-specific code are known as package plugins.In React Native, you would use yarn add {package-name} or
npm install --save {package-name} to install packages
from the command line.In Flutter, install a package using the following instructions:
<code_start>import 'package:flutter/material.dart';<code_end>
For more information, see Using Packages and
Developing Packages & Plugins.You can find many packages shared by Flutter developers in the
Flutter packages section of pub.dev.<topic_end>
<topic_start>
Flutter widgets
In Flutter, you build your UI out of widgets that describe what their view
should look like given their current configuration and state.Widgets are often composed of many small,
single-purpose widgets that are nested to produce powerful effects.
For example, the Container widget consists of
several widgets responsible for layout, painting, positioning, and sizing.
Specifically, the Container widget includes the LimitedBox,
ConstrainedBox, Align, Padding, DecoratedBox, and Transform widgets.
Rather than subclassing Container to produce a customized effect, you can
compose these and other simple widgets in new and unique ways.The Center widget is another example of how you can control the layout.
To center a widget, wrap it in a Center widget and then use layout
widgets for alignment, row, columns, and grids.
These layout widgets do not have a visual representation of their own.
Instead, their sole purpose is to control some aspect of another
widget’s layout. To understand why a widget renders in a
certain way, it’s often helpful to inspect the neighboring widgets.For more information, see the Flutter Technical Overview.For more information about the core widgets from the Widgets package,
see Flutter Basic Widgets,
the Flutter Widget Catalog,
or the Flutter Widget Index.<topic_end>
<topic_start>
Views
<topic_end>
<topic_start>
What is the equivalent of the View container?
In React Native, View is a container that supports layout with Flexbox,
style, touch handling, and accessibility controls.In Flutter, you can use the core layout widgets in the Widgets
library, such as Container, Column,
Row, and Center.
For more information, see the Layout Widgets catalog.<topic_end>
<topic_start>
What is the equivalent of FlatList or SectionList?
A List is a scrollable list of components arranged vertically.In React Native, FlatList or SectionList are used to render simple or
sectioned lists.ListView is Flutter’s most commonly used scrolling widget.
The default constructor takes an explicit list of children.
ListView is most appropriate for a small number of widgets.
For a large or infinite list, use ListView.builder,
which builds its children on demand and only builds
those children that are visible.
<code_start>var data = [
'Hello',
'World',
];
return ListView.builder(
itemCount: data.length,
itemBuilder: (context, index) {
return Text(data[index]);
},
);<code_end>
To learn how to implement an infinite scrolling list, see the official
infinite_list sample.<topic_end>
<topic_start>
How do I use a Canvas to draw or paint?
In React Native, canvas components aren’t present
so third party libraries like react-native-canvas are used.In Flutter, you can use the CustomPaint
and CustomPainter classes to draw to the canvas.The following example shows how to draw during the paint phase using the
CustomPaint widget. It implements the abstract class, CustomPainter,
and passes it to CustomPaint’s painter property.
CustomPaint subclasses must implement the paint()
and shouldRepaint() methods.
<code_start>class MyCanvasPainter extends CustomPainter {
const MyCanvasPainter();
@override
void paint(Canvas canvas, Size size) {
final Paint paint = Paint()..color = Colors.amber;
canvas.drawCircle(const Offset(100, 200), 40, paint);
final Paint paintRect = Paint()..color = Colors.lightBlue;
final Rect rect = Rect.fromPoints(
const Offset(150, 300),
const Offset(300, 400),
);
canvas.drawRect(rect, paintRect);
}
@override
bool shouldRepaint(MyCanvasPainter oldDelegate) => false;
}
class MyCanvasWidget extends StatelessWidget {
const MyCanvasWidget({super.key});
@override
Widget build(BuildContext context) {
return const Scaffold(
body: CustomPaint(painter: MyCanvasPainter()),
);
}