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// Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
import 'framework.dart';
import 'navigator.dart';
import 'will_pop_scope.dart';
/// An optional container for grouping together multiple form field widgets
/// (e.g. [TextField] widgets).
///
/// Each individual form field should be wrapped in a [FormField] widget, with
/// the [Form] widget as a common ancestor of all of those. Call methods on
/// [FormState] to save, reset, or validate each [FormField] that is a
/// descendant of this [Form]. To obtain the [FormState], you may use [Form.of]
/// with a context whose ancestor is the [Form], or pass a [GlobalKey] to the
/// [Form] constructor and call [GlobalKey.currentState].
///
/// {@tool snippet --template=stateful_widget_scaffold}
/// This example shows a [Form] with one [TextFormField] to enter an email
/// address and a [RaisedButton] to submit the form. A [GlobalKey] is used here
/// to identify the [Form] and validate input.
///
/// ![](https://flutter.github.io/assets-for-api-docs/assets/widgets/form.png)
///
/// ```dart
/// final _formKey = GlobalKey<FormState>();
///
/// @override
/// Widget build(BuildContext context) {
/// return Form(
/// key: _formKey,
/// child: Column(
/// crossAxisAlignment: CrossAxisAlignment.start,
/// children: <Widget>[
/// TextFormField(
/// decoration: const InputDecoration(
/// hintText: 'Enter your email',
/// ),
/// validator: (value) {
/// if (value.isEmpty) {
/// return 'Please enter some text';
/// }
/// return null;
/// },
/// ),
/// Padding(
/// padding: const EdgeInsets.symmetric(vertical: 16.0),
/// child: RaisedButton(
/// onPressed: () {
/// // Validate will return true if the form is valid, or false if
/// // the form is invalid.
/// if (_formKey.currentState.validate()) {
/// // Process data.
/// }
/// },
/// child: Text('Submit'),
/// ),
/// ),
/// ],
/// ),
/// );
/// }
/// ```
/// {@end-tool}
///
/// See also:
///
/// * [GlobalKey], a key that is unique across the entire app.
/// * [FormField], a single form field widget that maintains the current state.
/// * [TextFormField], a convenience widget that wraps a [TextField] widget in a [FormField].
class Form extends StatefulWidget {
/// Creates a container for form fields.
///
/// The [child] argument must not be null.
const Form({
Key key,
@required this.child,
this.autovalidate = false,
this.onWillPop,
this.onChanged,
}) : assert(child != null),
super(key: key);
/// Returns the closest [FormState] which encloses the given context.
///
/// Typical usage is as follows:
///
/// ```dart
/// FormState form = Form.of(context);
/// form.save();
/// ```
static FormState of(BuildContext context) {
final _FormScope scope = context.inheritFromWidgetOfExactType(_FormScope);
return scope?._formState;
}
/// The widget below this widget in the tree.
///
/// This is the root of the widget hierarchy that contains this form.
///
/// {@macro flutter.widgets.child}
final Widget child;
/// If true, form fields will validate and update their error text
/// immediately after every change. Otherwise, you must call
/// [FormState.validate] to validate.
final bool autovalidate;
/// Enables the form to veto attempts by the user to dismiss the [ModalRoute]
/// that contains the form.
///
/// If the callback returns a Future that resolves to false, the form's route
/// will not be popped.
///
/// See also:
///
/// * [WillPopScope], another widget that provides a way to intercept the
/// back button.
final WillPopCallback onWillPop;
/// Called when one of the form fields changes.
///
/// In addition to this callback being invoked, all the form fields themselves
/// will rebuild.
final VoidCallback onChanged;
@override
FormState createState() => FormState();
}
/// State associated with a [Form] widget.
///
/// A [FormState] object can be used to [save], [reset], and [validate] every
/// [FormField] that is a descendant of the associated [Form].
///
/// Typically obtained via [Form.of].
class FormState extends State<Form> {
int _generation = 0;
final Set<FormFieldState<dynamic>> _fields = <FormFieldState<dynamic>>{};
// Called when a form field has changed. This will cause all form fields
// to rebuild, useful if form fields have interdependencies.
void _fieldDidChange() {
if (widget.onChanged != null)
widget.onChanged();
_forceRebuild();
}
void _forceRebuild() {
setState(() {
++_generation;
});
}
void _register(FormFieldState<dynamic> field) {
_fields.add(field);
}
void _unregister(FormFieldState<dynamic> field) {
_fields.remove(field);
}
@override
Widget build(BuildContext context) {
if (widget.autovalidate)
_validate();
return WillPopScope(
onWillPop: widget.onWillPop,
child: _FormScope(
formState: this,
generation: _generation,
child: widget.child,
),
);
}
/// Saves every [FormField] that is a descendant of this [Form].
void save() {
for (FormFieldState<dynamic> field in _fields)
field.save();
}
/// Resets every [FormField] that is a descendant of this [Form] back to its
/// [FormField.initialState].
///
/// The [Form.onChanged] callback will be called.
///
/// If the form's [Form.autovalidate] property is true, the fields will all be
/// revalidated after being reset.
void reset() {
for (FormFieldState<dynamic> field in _fields)
field.reset();
_fieldDidChange();
}
/// Validates every [FormField] that is a descendant of this [Form], and
/// returns true if there are no errors.
///
/// The form will rebuild to report the results.
bool validate() {
_forceRebuild();
return _validate();
}
bool _validate() {
bool hasError = false;
for (FormFieldState<dynamic> field in _fields)
hasError = !field.validate() || hasError;
return !hasError;
}
}
class _FormScope extends InheritedWidget {
const _FormScope({
Key key,
Widget child,
FormState formState,
int generation,
}) : _formState = formState,
_generation = generation,
super(key: key, child: child);
final FormState _formState;
/// Incremented every time a form field has changed. This lets us know when
/// to rebuild the form.
final int _generation;
/// The [Form] associated with this widget.
Form get form => _formState.widget;
@override
bool updateShouldNotify(_FormScope old) => _generation != old._generation;
}
/// Signature for validating a form field.
///
/// Returns an error string to display if the input is invalid, or null
/// otherwise.
///
/// Used by [FormField.validator].
typedef FormFieldValidator<T> = String Function(T value);
/// Signature for being notified when a form field changes value.
///
/// Used by [FormField.onSaved].
typedef FormFieldSetter<T> = void Function(T newValue);
/// Signature for building the widget representing the form field.
///
/// Used by [FormField.builder].
typedef FormFieldBuilder<T> = Widget Function(FormFieldState<T> field);
/// A single form field.
///
/// This widget maintains the current state of the form field, so that updates
/// and validation errors are visually reflected in the UI.
///
/// When used inside a [Form], you can use methods on [FormState] to query or
/// manipulate the form data as a whole. For example, calling [FormState.save]
/// will invoke each [FormField]'s [onSaved] callback in turn.
///
/// Use a [GlobalKey] with [FormField] if you want to retrieve its current
/// state, for example if you want one form field to depend on another.
///
/// A [Form] ancestor is not required. The [Form] simply makes it easier to
/// save, reset, or validate multiple fields at once. To use without a [Form],
/// pass a [GlobalKey] to the constructor and use [GlobalKey.currentState] to
/// save or reset the form field.
///
/// See also:
///
/// * [Form], which is the widget that aggregates the form fields.
/// * [TextField], which is a commonly used form field for entering text.
class FormField<T> extends StatefulWidget {
/// Creates a single form field.
///
/// The [builder] argument must not be null.
const FormField({
Key key,
@required this.builder,
this.onSaved,
this.validator,
this.initialValue,
this.autovalidate = false,
this.enabled = true,
}) : assert(builder != null),
super(key: key);
/// An optional method to call with the final value when the form is saved via
/// [FormState.save].
final FormFieldSetter<T> onSaved;
/// An optional method that validates an input. Returns an error string to
/// display if the input is invalid, or null otherwise.
///
/// The returned value is exposed by the [FormFieldState.errorText] property.
/// The [TextFormField] uses this to override the [InputDecoration.errorText]
/// value.
///
/// Alternating between error and normal state can cause the height of the
/// [TextFormField] to change if no other subtext decoration is set on the
/// field. To create a field whose height is fixed regardless of whether or
/// not an error is displayed, either wrap the [TextFormField] in a fixed
/// height parent like [SizedBox], or set the [TextFormField.helperText]
/// parameter to a space.
final FormFieldValidator<T> validator;
/// Function that returns the widget representing this form field. It is
/// passed the form field state as input, containing the current value and
/// validation state of this field.
final FormFieldBuilder<T> builder;
/// An optional value to initialize the form field to, or null otherwise.
final T initialValue;
/// If true, this form field will validate and update its error text
/// immediately after every change. Otherwise, you must call
/// [FormFieldState.validate] to validate. If part of a [Form] that
/// auto-validates, this value will be ignored.
final bool autovalidate;
/// Whether the form is able to receive user input.
///
/// Defaults to true. If [autovalidate] is true, the field will be validated.
/// Likewise, if this field is false, the widget will not be validated
/// regardless of [autovalidate].
final bool enabled;
@override
FormFieldState<T> createState() => FormFieldState<T>();
}
/// The current state of a [FormField]. Passed to the [FormFieldBuilder] method
/// for use in constructing the form field's widget.
class FormFieldState<T> extends State<FormField<T>> {
T _value;
String _errorText;
/// The current value of the form field.
T get value => _value;
/// The current validation error returned by the [FormField.validator]
/// callback, or null if no errors have been triggered. This only updates when
/// [validate] is called.
String get errorText => _errorText;
/// True if this field has any validation errors.
bool get hasError => _errorText != null;
/// Calls the [FormField]'s onSaved method with the current value.
void save() {
if (widget.onSaved != null)
widget.onSaved(value);
}
/// Resets the field to its initial value.
void reset() {
setState(() {
_value = widget.initialValue;
_errorText = null;
});
}
/// Calls [FormField.validator] to set the [errorText]. Returns true if there
/// were no errors.
bool validate() {
setState(() {
_validate();
});
return !hasError;
}
void _validate() {
if (widget.validator != null)
_errorText = widget.validator(_value);
}
/// Updates this field's state to the new value. Useful for responding to
/// child widget changes, e.g. [Slider]'s [Slider.onChanged] argument.
///
/// Triggers the [Form.onChanged] callback and, if the [Form.autovalidate]
/// field is set, revalidates all the fields of the form.
void didChange(T value) {
setState(() {
_value = value;
});
Form.of(context)?._fieldDidChange();
}
/// Sets the value associated with this form field.
///
/// This method should be only be called by subclasses that need to update
/// the form field value due to state changes identified during the widget
/// build phase, when calling `setState` is prohibited. In all other cases,
/// the value should be set by a call to [didChange], which ensures that
/// `setState` is called.
@protected
void setValue(T value) {
_value = value;
}
@override
void initState() {
super.initState();
_value = widget.initialValue;
}
@override
void deactivate() {
Form.of(context)?._unregister(this);
super.deactivate();
}
@override
Widget build(BuildContext context) {
// Only autovalidate if the widget is also enabled
if (widget.autovalidate && widget.enabled)
_validate();
Form.of(context)?._register(this);
return widget.builder(this);
}
}
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