text_form_field.dart

// Copyright 2015 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 'package:flutter/services.dart';
import 'package:flutter/widgets.dart';

import 'input_decorator.dart';
import 'text_field.dart';
import 'theme.dart';

/// A [FormField] that contains a [TextField].
///
/// This is a convenience widget that wraps a [TextField] widget in a
/// [FormField].
///
/// 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.
///
/// When a [controller] is specified, its [TextEditingController.text]
/// defines the [initialValue]. If this [FormField] is part of a scrolling
/// container that lazily constructs its children, like a [ListView] or a
/// [CustomScrollView], then a [controller] should be specified.
/// The controller's lifetime should be managed by a stateful widget ancestor
/// of the scrolling container.
///
/// If a [controller] is not specified, [initialValue] can be used to give
/// the automatically generated controller an initial value.
///
/// Remember to [dispose] of the [TextEditingController] when it is no longer needed.
/// This will ensure we discard any resources used by the object.
///
/// For a documentation about the various parameters, see [TextField].
///
/// {@tool sample}
///
/// Creates a [TextFormField] with an [InputDecoration] and validator function.
///
/// ![If the user enters valid text, the TextField appears normally without any warnings to the user](https://flutter.github.io/assets-for-api-docs/assets/material/text_form_field.png)
///
/// ![If the user enters invalid text, the error message returned from the validator function is displayed in dark red underneath the input](https://flutter.github.io/assets-for-api-docs/assets/material/text_form_field_error.png)
///
/// ```dart
/// TextFormField(
///   decoration: const InputDecoration(
///     icon: Icon(Icons.person),
///     hintText: 'What do people call you?',
///     labelText: 'Name *',
///   ),
///   onSaved: (String value) {
///     // This optional block of code can be used to run
///     // code when the user saves the form.
///   },
///   validator: (String value) {
///     return value.contains('@') ? 'Do not use the @ char.' : null;
///   },
/// )
/// ```
/// {@end-tool}
///
/// See also:
///
///  * <https://material.io/design/components/text-fields.html>
///  * [TextField], which is the underlying text field without the [Form]
///    integration.
///  * [InputDecorator], which shows the labels and other visual elements that
///    surround the actual text editing widget.
///  * Learn how to use a [TextEditingController] in one of our [cookbook recipe]s.(https://flutter.dev/docs/cookbook/forms/text-field-changes#2-use-a-texteditingcontroller)
class TextFormField extends FormField<String> {
  /// Creates a [FormField] that contains a [TextField].
  ///
  /// When a [controller] is specified, [initialValue] must be null (the
  /// default). If [controller] is null, then a [TextEditingController]
  /// will be constructed automatically and its `text` will be initialized
  /// to [initialValue] or the empty string.
  ///
  /// For documentation about the various parameters, see the [TextField] class
  /// and [new TextField], the constructor.
  TextFormField({
    Key key,
    this.controller,
    String initialValue,
    FocusNode focusNode,
    InputDecoration decoration = const InputDecoration(),
    TextInputType keyboardType,
    TextCapitalization textCapitalization = TextCapitalization.none,
    TextInputAction textInputAction,
    TextStyle style,
    StrutStyle strutStyle,
    TextDirection textDirection,
    TextAlign textAlign = TextAlign.start,
    TextAlignVertical textAlignVertical,
    bool autofocus = false,
    bool readOnly = false,
    ToolbarOptions toolbarOptions,
    bool showCursor,
    bool obscureText = false,
    bool autocorrect = true,
    bool enableSuggestions = true,
    bool autovalidate = false,
    bool maxLengthEnforced = true,
    int maxLines = 1,
    int minLines,
    bool expands = false,
    int maxLength,
    ValueChanged<String> onChanged,
    GestureTapCallback onTap,
    VoidCallback onEditingComplete,
    ValueChanged<String> onFieldSubmitted,
    FormFieldSetter<String> onSaved,
    FormFieldValidator<String> validator,
    List<TextInputFormatter> inputFormatters,
    bool enabled = true,
    double cursorWidth = 2.0,
    Radius cursorRadius,
    Color cursorColor,
    Brightness keyboardAppearance,
    EdgeInsets scrollPadding = const EdgeInsets.all(20.0),
    bool enableInteractiveSelection = true,
    InputCounterWidgetBuilder buildCounter,
  }) : assert(initialValue == null || controller == null),
       assert(textAlign != null),
       assert(autofocus != null),
       assert(readOnly != null),
       assert(obscureText != null),
       assert(autocorrect != null),
       assert(enableSuggestions != null),
       assert(autovalidate != null),
       assert(maxLengthEnforced != null),
       assert(scrollPadding != null),
       assert(maxLines == null || maxLines > 0),
       assert(minLines == null || minLines > 0),
       assert(
         (maxLines == null) || (minLines == null) || (maxLines >= minLines),
         'minLines can\'t be greater than maxLines',
       ),
       assert(expands != null),
       assert(
         !expands || (maxLines == null && minLines == null),
         'minLines and maxLines must be null when expands is true.',
       ),
       assert(!obscureText || maxLines == 1, 'Obscured fields cannot be multiline.'),
       assert(maxLength == null || maxLength > 0),
       assert(enableInteractiveSelection != null),
       super(
    key: key,
    initialValue: controller != null ? controller.text : (initialValue ?? ''),
    onSaved: onSaved,
    validator: validator,
    autovalidate: autovalidate,
    enabled: enabled,
    builder: (FormFieldState<String> field) {
      final _TextFormFieldState state = field;
      final InputDecoration effectiveDecoration = (decoration ?? const InputDecoration())
        .applyDefaults(Theme.of(field.context).inputDecorationTheme);
      void onChangedHandler(String value) {
        if (onChanged != null) {
          onChanged(value);
        }
        field.didChange(value);
      }
      return TextField(
        controller: state._effectiveController,
        focusNode: focusNode,
        decoration: effectiveDecoration.copyWith(errorText: field.errorText),
        keyboardType: keyboardType,
        textInputAction: textInputAction,
        style: style,
        strutStyle: strutStyle,
        textAlign: textAlign,
        textAlignVertical: textAlignVertical,
        textDirection: textDirection,
        textCapitalization: textCapitalization,
        autofocus: autofocus,
        toolbarOptions: toolbarOptions,
        readOnly: readOnly,
        showCursor: showCursor,
        obscureText: obscureText,
        autocorrect: autocorrect,
        enableSuggestions: enableSuggestions,
        maxLengthEnforced: maxLengthEnforced,
        maxLines: maxLines,
        minLines: minLines,
        expands: expands,
        maxLength: maxLength,
        onChanged: onChangedHandler,
        onTap: onTap,
        onEditingComplete: onEditingComplete,
        onSubmitted: onFieldSubmitted,
        inputFormatters: inputFormatters,
        enabled: enabled,
        cursorWidth: cursorWidth,
        cursorRadius: cursorRadius,
        cursorColor: cursorColor,
        scrollPadding: scrollPadding,
        keyboardAppearance: keyboardAppearance,
        enableInteractiveSelection: enableInteractiveSelection,
        buildCounter: buildCounter,
      );
    },
  );

  /// Controls the text being edited.
  ///
  /// If null, this widget will create its own [TextEditingController] and
  /// initialize its [TextEditingController.text] with [initialValue].
  final TextEditingController controller;

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

class _TextFormFieldState extends FormFieldState<String> {
  TextEditingController _controller;

  TextEditingController get _effectiveController => widget.controller ?? _controller;

  @override
  TextFormField get widget => super.widget;

  @override
  void initState() {
    super.initState();
    if (widget.controller == null) {
      _controller = TextEditingController(text: widget.initialValue);
    } else {
      widget.controller.addListener(_handleControllerChanged);
    }
  }

  @override
  void didUpdateWidget(TextFormField oldWidget) {
    super.didUpdateWidget(oldWidget);
    if (widget.controller != oldWidget.controller) {
      oldWidget.controller?.removeListener(_handleControllerChanged);
      widget.controller?.addListener(_handleControllerChanged);

      if (oldWidget.controller != null && widget.controller == null)
        _controller = TextEditingController.fromValue(oldWidget.controller.value);
      if (widget.controller != null) {
        setValue(widget.controller.text);
        if (oldWidget.controller == null)
          _controller = null;
      }
    }
  }

  @override
  void dispose() {
    widget.controller?.removeListener(_handleControllerChanged);
    super.dispose();
  }

  @override
  void reset() {
    super.reset();
    setState(() {
      _effectiveController.text = widget.initialValue;
    });
  }

  void _handleControllerChanged() {
    // Suppress changes that originated from within this class.
    //
    // In the case where a controller has been passed in to this widget, we
    // register this change listener. In these cases, we'll also receive change
    // notifications for changes originating from within this class -- for
    // example, the reset() method. In such cases, the FormField value will
    // already have been set.
    if (_effectiveController.text != value)
      didChange(_effectiveController.text);
  }
}