Flutter Dart Form 源码

class Form extends StatefulWidget {
  /// Creates a container for form fields.
  ///
  /// The [child] argument must not be null.
  const Form({
    super.key,
    required this.child,
    this.onWillPop,
    this.onChanged,
    AutovalidateMode? autovalidateMode,
  }) : assert(child != null),
       autovalidateMode = autovalidateMode ?? AutovalidateMode.disabled;

  /// 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.dependOnInheritedWidgetOfExactType<_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.ProxyWidget.child}
  final Widget child;

  /// 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;

  /// Used to enable/disable form fields auto validation and update their error
  /// text.
  ///
  /// {@macro flutter.widgets.FormField.autovalidateMode}
  final AutovalidateMode autovalidateMode;

  @override
  FormState createState() => FormState();
}

这个构造函数接受了以下参数：

• key：表示组件的唯一标识符。它继承自 StatefulWidget 类，是可选的。
• child：表示组件的内容。它是必填的。
• onWillPop：当表单即将被弹出（例如用户点击了返回按钮）时调用的回调函数。它是可选的。
• onChanged：当表单内容发生改变时调用的回调函数。它是可选的。
• autovalidateMode：表示表单自动验证的模式。它是可选的，默认值为 AutovalidateMode.disabled。