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instead, when the user has entered invalid data,
update the state, and pass a new InputDecoration object.
<code_start>
import 'package:flutter/material.dart';
void main() {
runApp(const SampleApp());
}
class SampleApp extends StatelessWidget {
/// this widget is the root of your application.
const SampleApp({super.key});
@override
widget build(BuildContext context) {
return const MaterialApp(
title: 'sample app',
home: SampleAppPage(),
);
}
}
class SampleAppPage extends StatefulWidget {
const SampleAppPage({super.key});
@override
State<SampleAppPage> createState() => _SampleAppPageState();
}
class _SampleAppPageState extends State<SampleAppPage> {
string? _errorText;
string? _getErrorText() {
return _errorText;
}
bool isEmail(String em) {
const string emailRegexp =
r'^(([^<>()[\]\\.,;:\s@\"]+(\.[^<>()[\]\\.,;:\s@\"]+)*)|'
r'(\".+\"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|'
r'(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$';
final RegExp regExp = RegExp(emailRegexp);
return regExp.hasMatch(em);
}
@override
widget build(BuildContext context) {
return scaffold(
appBar: AppBar(title: const Text('Sample app')),
body: center(
child: TextField(
onSubmitted: (text) {
setState(() {
if (!isemail(text)) {
_errorText = 'error: this is not an email';
} else {
_errorText = null;
}
});
},
decoration: InputDecoration(
hintText: 'this is a hint',
errorText: _getErrorText(),
),
),
),
);
}
}
<code_end>
<topic_end>
<topic_start>
flutter plugins
<topic_end>
<topic_start>
interacting with hardware, third party services, and the platform
<topic_end>
<topic_start>
how do i interact with the platform, and with platform native code?
flutter doesn’t run code directly on the underlying platform;
rather, the dart code that makes up a flutter app is run natively
on the device, “sidestepping” the SDK provided by the platform.
that means, for example, when you perform a network request in dart,
it runs directly in the dart context.
you don’t use the android or iOS APIs
you normally take advantage of when writing native apps.
your flutter app is still hosted in a native app’s
ViewController or activity as a view,
but you don’t have direct access to this, or the native framework.
this doesn’t mean flutter apps can’t interact with those native APIs,
or with any native code you have. flutter provides platform channels
that communicate and exchange data with the
ViewController or activity that hosts your flutter view.
platform channels are essentially an asynchronous messaging mechanism
that bridges the dart code with the host ViewController
or activity and the iOS or android framework it runs on.
you can use platform channels to execute a method on the native side,
or to retrieve some data from the device’s sensors, for example.
in addition to directly using platform channels,
you can use a variety of pre-made plugins
that encapsulate the native and dart code for a specific goal.
for example, you can use a plugin to access
the camera roll and the device camera directly from flutter,
without having to write your own integration.
plugins are found on pub.dev,
dart and flutter’s open source package repository.
some packages might support native integrations on iOS,
or android, or both.
if you can’t find a plugin on pub.dev that fits your needs,