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),
ElevatedButton(
child: const Text('Submit'),
onPressed: () {
showDialog(
context: context,
builder: (context) {
return AlertDialog(
title: const Text('Alert'),
content: Text('You typed ${_controller.text}'),
);
});
},
),
]);
}<code_end>
In this example, when a user clicks on the submit button an alert dialog
displays the current text entered in the text field.
This is achieved using an AlertDialog
widget that displays the alert message, and the text from
the TextField is accessed by the text property of the
TextEditingController.<topic_end>
<topic_start>
How do I use Form widgets?
In Flutter, use the Form widget where
TextFormField widgets along with the submit
button are passed as children.
The TextFormField widget has a parameter called
onSaved that takes a callback and executes
when the form is saved. A FormState
object is used to save, reset, or validate
each FormField that is a descendant of this Form.
To obtain the FormState, you can use Form.of()
with a context whose ancestor is the Form,
or pass a GlobalKey to the Form constructor and call
GlobalKey.currentState().
<code_start>@override
Widget build(BuildContext context) {
return Form(
key: formKey,
child: Column(
children: <Widget>[
TextFormField(
validator: (value) {
if (value != null && value.contains('@')) {
return null;
}
return 'Not a valid email.';
},
onSaved: (val) {
_email = val;
},
decoration: const InputDecoration(
hintText: 'Enter your email',
labelText: 'Email',
),
),
ElevatedButton(
onPressed: _submit,
child: const Text('Login'),
),
],
),
);
}<code_end>
The following example shows how Form.save() and formKey
(which is a GlobalKey), are used to save the form on submit.
<code_start>void _submit() {
final form = formKey.currentState;
if (form != null && form.validate()) {
form.save();
showDialog(
context: context,
builder: (context) {
return AlertDialog(
title: const Text('Alert'),
content: Text('Email: $_email, password: $_password'));
},
);
}
}<code_end>
<topic_end>
<topic_start>
Platform-specific code
When building a cross-platform app, you want to re-use as much code as
possible across platforms. However, scenarios might arise where it
makes sense for the code to be different depending on the OS.
This requires a separate implementation by declaring a specific platform.In React Native, the following implementation would be used:In Flutter, use the following implementation:
<code_start>final platform = Theme.of(context).platform;
if (platform == TargetPlatform.iOS) {
return 'iOS';
}
if (platform == TargetPlatform.android) {
return 'android';
}
if (platform == TargetPlatform.fuchsia) {
return 'fuchsia';
}
return 'not recognized ';<code_end>
<topic_end>