packages/flutter/lib/src/material/input_decorator.dart - external/github.com/flutter/flutter - Git at Google

 // 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/foundation.dart';
 import 'package:flutter/widgets.dart';

 import 'colors.dart';
 import 'debug.dart';
 import 'theme.dart';

 const Duration _kTransitionDuration = const Duration(milliseconds: 200);
 const Curve _kTransitionCurve = Curves.fastOutSlowIn;

 // See the InputDecorator.build method, where this is used.
 class _InputDecoratorChildGlobalKey extends GlobalObjectKey {
   const _InputDecoratorChildGlobalKey(BuildContext value) : super(value);
 }

 /// Text and styles used to label an input field.
 ///
 /// The [TextField] and [InputDecorator] classes use [InputDecoration] objects
 /// to describe their decoration. (In fact, this class is merely the
 /// configuration of an [InputDecorator], which does all the heavy lifting.)
 ///
 /// See also:
 ///
 ///  * [TextField], which is a text input widget that uses an
 ///    [InputDecoration].
 ///  * [InputDecorator], which is a widget that draws an [InputDecoration]
 ///    around an arbitrary child widget.
 ///  * [Decoration] and [DecoratedBox], for drawing arbitrary decorations
 ///    around other widgets.
 @immutable
 class InputDecoration {
   /// Creates a bundle of text and styles used to label an input field.
   ///
   /// Sets the [isCollapsed] property to false. To create a decoration that does
   /// not reserve space for [labelText] or [errorText], use
   /// [InputDecoration.collapsed].
   const InputDecoration({
     this.icon,
     this.labelText,
     this.labelStyle,
     this.helperText,
     this.helperStyle,
     this.hintText,
     this.hintStyle,
     this.errorText,
     this.errorStyle,
     this.isDense: false,
     this.hideDivider: false,
     this.prefixText,
     this.prefixStyle,
     this.suffixText,
     this.suffixStyle,
   }) : isCollapsed = false;

   /// Creates a decoration that is the same size as the input field.
   ///
   /// This type of input decoration does not include a divider or an icon and
   /// does not reserve space for [labelText] or [errorText].
   ///
   /// Sets the [isCollapsed] property to true.
   const InputDecoration.collapsed({
     @required this.hintText,
     this.hintStyle,
   }) : icon = null,
        labelText = null,
        labelStyle = null,
        helperText = null,
        helperStyle = null,
        errorText = null,
        errorStyle = null,
        isDense = false,
        isCollapsed = true,
        hideDivider = true,
        prefixText = null,
        prefixStyle = null,
        suffixText = null,
        suffixStyle = null;

   /// An icon to show before the input field.
   ///
   /// The size and color of the icon is configured automatically using an
   /// [IconTheme] and therefore does not need to be explicitly given in the
   /// icon widget.
   ///
   /// See [Icon], [ImageIcon].
   final Widget icon;

   /// Text that describes the input field.
   ///
   /// When the input field is empty and unfocused, the label is displayed on
   /// top of the input field (i.e., at the same location on the screen where
   /// text my be entered in the input field). When the input field receives
   /// focus (or if the field is non-empty), the label moves above (i.e.,
   /// vertically adjacent to) the input field.
   final String labelText;

   /// The style to use for the [labelText] when the label is above (i.e.,
   /// vertically adjacent to) the input field.
   ///
   /// When the [labelText] is on top of the input field, the text uses the
   /// [hintStyle] instead.
   ///
   /// If null, defaults of a value derived from the base [TextStyle] for the
   /// input field and the current [Theme].
   final TextStyle labelStyle;

   /// Text that provides context about the field’s value, such as how the value
   /// will be used.
   ///
   /// If non-null, the text is displayed below the input field, in the same
   /// location as [errorText]. If a non-null [errorText] value is specified then
   /// the helper text is not shown.
   final String helperText;

   /// The style to use for the [helperText].
   final TextStyle helperStyle;

   /// Text that suggests what sort of input the field accepts.
   ///
   /// Displayed on top of the input field (i.e., at the same location on the
   /// screen where text my be entered in the input field) when the input field
   /// is empty and either (a) [labelText] is null or (b) the input field has
   /// focus.
   final String hintText;

   /// The style to use for the [hintText].
   ///
   /// Also used for the [labelText] when the [labelText] is displayed on
   /// top of the input field (i.e., at the same location on the screen where
   /// text my be entered in the input field).
   ///
   /// If null, defaults of a value derived from the base [TextStyle] for the
   /// input field and the current [Theme].
   final TextStyle hintStyle;

   /// Text that appears below the input field.
   ///
   /// If non-null, the divider that appears below the input field is red.
   final String errorText;

   /// The style to use for the [errorText].
   ///
   /// If null, defaults of a value derived from the base [TextStyle] for the
   /// input field and the current [Theme].
   final TextStyle errorStyle;

   /// Whether the input field is part of a dense form (i.e., uses less vertical
   /// space).
   ///
   /// Defaults to false.
   final bool isDense;

   /// Whether the decoration is the same size as the input field.
   ///
   /// A collapsed decoration cannot have [labelText], [errorText], an [icon], or
   /// a divider because those elements require extra space.
   ///
   /// To create a collapsed input decoration, use [InputDecoration..collapsed].
   final bool isCollapsed;

   /// Whether to hide the divider below the input field and above the error text.
   ///
   /// Defaults to false.
   final bool hideDivider;

   /// Optional text prefix to place on the line before the input.
   ///
   /// Uses the [prefixStyle]. Uses [hintStyle] if [prefixStyle] isn't
   /// specified. Prefix is not returned as part of the input.
   final String prefixText;

   /// The style to use for the [prefixText].
   ///
   /// If null, defaults to the [hintStyle].
   final TextStyle prefixStyle;

   /// Optional text suffix to place on the line after the input.
   ///
   /// Uses the [suffixStyle]. Uses [hintStyle] if [suffixStyle] isn't
   /// specified. Suffix is not returned as part of the input.
   final String suffixText;

   /// The style to use for the [suffixText].
   ///
   /// If null, defaults to the [hintStyle].
   final TextStyle suffixStyle;

   /// Creates a copy of this input decoration but with the given fields replaced
   /// with the new values.
   ///
   /// Always sets [isCollapsed] to false.
   InputDecoration copyWith({
     Widget icon,
     String labelText,
     TextStyle labelStyle,
     String helperText,
     TextStyle helperStyle,
     String hintText,
     TextStyle hintStyle,
     String errorText,
     TextStyle errorStyle,
     bool isDense,
     bool hideDivider,
     String prefixText,
     TextStyle prefixStyle,
     String suffixText,
     TextStyle suffixStyle,
   }) {
     return new InputDecoration(
       icon: icon ?? this.icon,
       labelText: labelText ?? this.labelText,
       labelStyle: labelStyle ?? this.labelStyle,
       helperText: helperText ?? this.helperText,
       helperStyle: helperStyle ?? this.helperStyle,
       hintText: hintText ?? this.hintText,
       hintStyle: hintStyle ?? this.hintStyle,
       errorText: errorText ?? this.errorText,
       errorStyle: errorStyle ?? this.errorStyle,
       isDense: isDense ?? this.isDense,
       hideDivider: hideDivider ?? this.hideDivider,
       prefixText: prefixText ?? this.prefixText,
       prefixStyle: prefixStyle ?? this.prefixStyle,
       suffixText: suffixText ?? this.suffixText,
       suffixStyle: suffixStyle ?? this.suffixStyle,
     );
   }

   @override
   bool operator ==(dynamic other) {
     if (identical(this, other))
       return true;
     if (other.runtimeType != runtimeType)
       return false;
     final InputDecoration typedOther = other;
     return typedOther.icon == icon
         && typedOther.labelText == labelText
         && typedOther.labelStyle == labelStyle
         && typedOther.helperText == helperText
         && typedOther.helperStyle == helperStyle
         && typedOther.hintText == hintText
         && typedOther.hintStyle == hintStyle
         && typedOther.errorText == errorText
         && typedOther.errorStyle == errorStyle
         && typedOther.isDense == isDense
         && typedOther.isCollapsed == isCollapsed
         && typedOther.hideDivider == hideDivider
         && typedOther.prefixText == prefixText
         && typedOther.prefixStyle == prefixStyle
         && typedOther.suffixText == suffixText
         && typedOther.suffixStyle == suffixStyle;
   }

   @override
   int get hashCode {
     return hashValues(
       icon,
       labelText,
       labelStyle,
       helperText,
       helperStyle,
       hintText,
       hintStyle,
       errorText,
       errorStyle,
       isDense,
       isCollapsed,
       hideDivider,
       prefixText,
       prefixStyle,
       suffixText,
       suffixStyle,
     );
   }

   @override
   String toString() {
     final List<String> description = <String>[];
     if (icon != null)
       description.add('icon: $icon');
     if (labelText != null)
       description.add('labelText: "$labelText"');
     if (helperText != null)
       description.add('helperText: "$helperText"');
     if (hintText != null)
       description.add('hintText: "$hintText"');
     if (errorText != null)
       description.add('errorText: "$errorText"');
     if (isDense)
       description.add('isDense: $isDense');
     if (isCollapsed)
       description.add('isCollapsed: $isCollapsed');
     if (hideDivider)
       description.add('hideDivider: $hideDivider');
     if (prefixText != null)
       description.add('prefixText: $prefixText');
     if (prefixStyle != null)
       description.add('prefixStyle: $prefixStyle');
     if (suffixText != null)
       description.add('suffixText: $suffixText');
     if (suffixStyle != null)
       description.add('suffixStyle: $suffixStyle');
     return 'InputDecoration(${description.join(', ')})';
   }
 }

 /// Displays the visual elements of a Material Design text field around an
 /// arbitrary widget.
 ///
 /// Use [InputDecorator] to create widgets that look and behave like a
 /// [TextField] but can be used to input information other than text.
 ///
 /// The configuration of this widget is primarily provided in the form of an
 /// [InputDecoration] object.
 ///
 /// Requires one of its ancestors to be a [Material] widget.
 ///
 /// See also:
 ///
 ///  * [TextField], which uses an [InputDecorator] to draw labels and other
 ///    visual elements around a text entry widget.
 ///  * [Decoration] and [DecoratedBox], for drawing arbitrary decorations
 ///    around other widgets.
 class InputDecorator extends StatelessWidget {
   /// Creates a widget that displayes labels and other visual elements similar
   /// to a [TextField].
   ///
   /// The [isFocused] and [isEmpty] arguments must not be null.
   const InputDecorator({
     Key key,
     @required this.decoration,
     this.baseStyle,
     this.textAlign,
     this.isFocused: false,
     this.isEmpty: false,
     this.child,
   }) : assert(isFocused != null),
        assert(isEmpty != null),
        super(key: key);

   /// The text and styles to use when decorating the child.
   final InputDecoration decoration;

   /// The style on which to base the label, hint, and error styles if the
   /// [decoration] does not provide explicit styles.
   ///
   /// If null, defaults to a text style from the current [Theme].
   final TextStyle baseStyle;

   /// How the text in the decoration should be aligned horizontally.
   final TextAlign textAlign;

   /// Whether the input field has focus.
   ///
   /// Determines the position of the label text and the color of the divider.
   ///
   /// Defaults to false.
   final bool isFocused;

   /// Whether the input field is empty.
   ///
   /// Determines the position of the label text and whether to display the hint
   /// text.
   ///
   /// Defaults to false.
   final bool isEmpty;

   /// The widget below this widget in the tree.
   final Widget child;

   @override
   void debugFillProperties(DiagnosticPropertiesBuilder description) {
     super.debugFillProperties(description);
     description.add(new DiagnosticsProperty<InputDecoration>('decoration', decoration));
     description.add(new EnumProperty<TextStyle>('baseStyle', baseStyle));
     description.add(new DiagnosticsProperty<bool>('isFocused', isFocused));
     description.add(new DiagnosticsProperty<bool>('isEmpty', isEmpty));
   }

   Color _getActiveColor(ThemeData themeData) {
     if (isFocused) {
       switch (themeData.brightness) {
         case Brightness.dark:
           return themeData.accentColor;
         case Brightness.light:
           return themeData.primaryColor;
       }
     }
     return themeData.hintColor;
   }

   Widget _buildContent(Color borderColor, double topPadding, bool isDense, Widget inputChild) {
     final double bottomPadding = isDense ? 8.0 : 1.0;
     const double bottomBorder = 2.0;
     final double bottomHeight = isDense ? 14.0 : 18.0;

     final EdgeInsets padding = new EdgeInsets.only(top: topPadding, bottom: bottomPadding);
     final EdgeInsets margin = new EdgeInsets.only(bottom: bottomHeight - (bottomPadding + bottomBorder));

     if (decoration.hideDivider) {
       return new Container(
         margin: margin + const EdgeInsets.only(bottom: bottomBorder),
         padding: padding,
         child: inputChild,
       );
     }

     return new AnimatedContainer(
       margin: margin,
       padding: padding,
       duration: _kTransitionDuration,
       curve: _kTransitionCurve,
       decoration: new BoxDecoration(
         border: new Border(
           bottom: new BorderSide(
             color: borderColor,
             width: bottomBorder,
           ),
         ),
       ),
       child: inputChild,
     );
   }

   @override
   Widget build(BuildContext context) {
     assert(debugCheckHasMaterial(context));
     final ThemeData themeData = Theme.of(context);

     final bool isDense = decoration.isDense;
     final bool isCollapsed = decoration.isCollapsed;
     assert(!isDense || !isCollapsed);

     final String labelText = decoration.labelText;
     final String helperText = decoration.helperText;
     final String hintText = decoration.hintText;
     final String errorText = decoration.errorText;

     final TextStyle baseStyle = this.baseStyle ?? themeData.textTheme.subhead;
     final TextStyle hintStyle = decoration.hintStyle ?? baseStyle.copyWith(color: themeData.hintColor);

     final Color activeColor = _getActiveColor(themeData);

     double topPadding = isCollapsed ? 0.0 : (isDense ? 12.0 : 16.0);

     final List<Widget> stackChildren = <Widget>[];

     // If we're not focused, there's no value, and labelText was provided,
     // then the label appears where the hint would. And we will not show
     // the hintText.
     final bool hasInlineLabel = !isFocused && labelText != null && isEmpty;

     if (labelText != null) {
       assert(!isCollapsed);
       final TextStyle labelStyle = hasInlineLabel ?
         hintStyle : (decoration.labelStyle ?? themeData.textTheme.caption.copyWith(color: activeColor));

       final double topPaddingIncrement = themeData.textTheme.caption.fontSize + (isDense ? 4.0 : 8.0);
       double top = topPadding;
       if (hasInlineLabel)
         top += topPaddingIncrement + baseStyle.fontSize - labelStyle.fontSize;

       stackChildren.add(
         new AnimatedPositioned(
           left: 0.0,
           top: top,
           duration: _kTransitionDuration,
           curve: _kTransitionCurve,
           child: new _AnimatedLabel(
             text: labelText,
             style: labelStyle,
             duration: _kTransitionDuration,
             curve: _kTransitionCurve,
           ),
         ),
       );

       topPadding += topPaddingIncrement;
     }

     if (hintText != null) {
       stackChildren.add(
         new Positioned(
           left: 0.0,
           right: 0.0,
           top: topPadding + baseStyle.fontSize - hintStyle.fontSize,
           child: new AnimatedOpacity(
             opacity: (isEmpty && !hasInlineLabel) ? 1.0 : 0.0,
             duration: _kTransitionDuration,
             curve: _kTransitionCurve,
             child: new Text(
               hintText,
               style: hintStyle,
               overflow: TextOverflow.ellipsis,
               textAlign: textAlign,
             ),
           ),
         ),
       );
     }

     Widget inputChild = new KeyedSubtree(
       // It's important that we maintain the state of our child subtree, as it
       // may be stateful (e.g. containing text selections). Since our build
       // function risks changing the depth of the tree, we preserve the subtree
       // using global keys.
       // GlobalObjectKey(context) will always be the same whenever we are built.
       // Additionally, we use a subclass of GlobalObjectKey to avoid clashes
       // with anyone else using our BuildContext as their global object key
       // value.
       key: new _InputDecoratorChildGlobalKey(context),
       child: child,
     );

     if (!hasInlineLabel && (!isEmpty || hintText == null) &&
         (decoration?.prefixText != null || decoration?.suffixText != null)) {
       final List<Widget> rowContents = <Widget>[];
       if (decoration.prefixText != null) {
         rowContents.add(
             new Text(decoration.prefixText,
             style: decoration.prefixStyle ?? hintStyle)
         );
       }
       rowContents.add(new Expanded(child: inputChild));
       if (decoration.suffixText != null) {
         rowContents.add(
             new Text(decoration.suffixText,
             style: decoration.suffixStyle ?? hintStyle)
         );
       }
       inputChild = new Row(children: rowContents);
     }

     if (isCollapsed) {
       stackChildren.add(inputChild);
     } else {
       final Color borderColor = errorText == null ? activeColor : themeData.errorColor;
       stackChildren.add(_buildContent(borderColor, topPadding, isDense, inputChild));
     }

     if (!isDense && (errorText != null || helperText != null)) {
       assert(!isCollapsed);
       final TextStyle captionStyle = themeData.textTheme.caption;
       final TextStyle subtextStyle = errorText != null
         ? decoration.errorStyle ?? captionStyle.copyWith(color: themeData.errorColor)
         : decoration.helperStyle ?? captionStyle.copyWith(color: themeData.hintColor);

       stackChildren.add(new Positioned(
         left: 0.0,
         right: 0.0,
         bottom: 0.0,
         child: new Text(
           errorText ?? helperText,
           style: subtextStyle,
           textAlign: textAlign,
           overflow: TextOverflow.ellipsis,
         ),
       ));
     }

     final Widget stack = new Stack(
       fit: StackFit.passthrough,
       children: stackChildren
     );

     if (decoration.icon != null) {
       assert(!isCollapsed);
       final double iconSize = isDense ? 18.0 : 24.0;
       final double iconTop = topPadding + (baseStyle.fontSize - iconSize) / 2.0;
       return new Row(
         crossAxisAlignment: CrossAxisAlignment.start,
         children: <Widget>[
           new Container(
             margin: new EdgeInsets.only(top: iconTop),
             width: isDense ? 40.0 : 48.0,
             child: IconTheme.merge(
               data: new IconThemeData(
                 color: isFocused ? activeColor : Colors.black45,
                 size: isDense ? 18.0 : 24.0,
               ),
               child: decoration.icon,
             ),
           ),
           new Expanded(child: stack),
         ],
       );
     } else {
       return new ConstrainedBox(
         constraints: const BoxConstraints(minWidth: double.INFINITY),
         child: stack,
       );
     }
   }
 }

 // Smoothly animate the label of an InputDecorator as the label
 // transitions between inline and caption.
 class _AnimatedLabel extends ImplicitlyAnimatedWidget {
   const _AnimatedLabel({
     Key key,
     this.text,
     @required this.style,
     Curve curve: Curves.linear,
     @required Duration duration,
   }) : assert(style != null),
        super(key: key, curve: curve, duration: duration);

   final String text;
   final TextStyle style;

   @override
   _AnimatedLabelState createState() => new _AnimatedLabelState();

   @override
   void debugFillProperties(DiagnosticPropertiesBuilder description) {
     super.debugFillProperties(description);
     style?.debugFillProperties(description);
   }
 }

 class _AnimatedLabelState extends AnimatedWidgetBaseState<_AnimatedLabel> {
   TextStyleTween _style;

   @override
   void forEachTween(TweenVisitor<dynamic> visitor) {
     _style = visitor(_style, widget.style, (dynamic value) => new TextStyleTween(begin: value));
   }

   @override
   Widget build(BuildContext context) {
     TextStyle style = _style.evaluate(animation);
     double scale = 1.0;
     if (style.fontSize != widget.style.fontSize) {
       // While the fontSize is transitioning, use a scaled Transform as a
       // fraction of the original fontSize. That way we get a smooth scaling
       // effect with no snapping between discrete font sizes.
       scale = style.fontSize / widget.style.fontSize;
       style = style.copyWith(fontSize: widget.style.fontSize);
     }

     return new Transform(
       transform: new Matrix4.identity()..scale(scale),
       child: new Text(
         widget.text,
         style: style,
       ),
     );
   }
 }
	// 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/foundation.dart';
	import 'package:flutter/widgets.dart';

	import 'colors.dart';
	import 'debug.dart';
	import 'theme.dart';

	const Duration _kTransitionDuration = const Duration(milliseconds: 200);
	const Curve _kTransitionCurve = Curves.fastOutSlowIn;

	// See the InputDecorator.build method, where this is used.
	class _InputDecoratorChildGlobalKey extends GlobalObjectKey {
	const _InputDecoratorChildGlobalKey(BuildContext value) : super(value);
	}

	/// Text and styles used to label an input field.
	///
	/// The [TextField] and [InputDecorator] classes use [InputDecoration] objects
	/// to describe their decoration. (In fact, this class is merely the
	/// configuration of an [InputDecorator], which does all the heavy lifting.)
	///
	/// See also:
	///
	/// * [TextField], which is a text input widget that uses an
	/// [InputDecoration].
	/// * [InputDecorator], which is a widget that draws an [InputDecoration]
	/// around an arbitrary child widget.
	/// * [Decoration] and [DecoratedBox], for drawing arbitrary decorations
	/// around other widgets.
	@immutable
	class InputDecoration {
	/// Creates a bundle of text and styles used to label an input field.
	///
	/// Sets the [isCollapsed] property to false. To create a decoration that does
	/// not reserve space for [labelText] or [errorText], use
	/// [InputDecoration.collapsed].
	const InputDecoration({
	this.icon,
	this.labelText,
	this.labelStyle,
	this.helperText,
	this.helperStyle,
	this.hintText,
	this.hintStyle,
	this.errorText,
	this.errorStyle,
	this.isDense: false,
	this.hideDivider: false,
	this.prefixText,
	this.prefixStyle,
	this.suffixText,
	this.suffixStyle,
	}) : isCollapsed = false;

	/// Creates a decoration that is the same size as the input field.
	///
	/// This type of input decoration does not include a divider or an icon and
	/// does not reserve space for [labelText] or [errorText].
	///
	/// Sets the [isCollapsed] property to true.
	const InputDecoration.collapsed({
	@required this.hintText,
	this.hintStyle,
	}) : icon = null,
	labelText = null,
	labelStyle = null,
	helperText = null,
	helperStyle = null,
	errorText = null,
	errorStyle = null,
	isDense = false,
	isCollapsed = true,
	hideDivider = true,
	prefixText = null,
	prefixStyle = null,
	suffixText = null,
	suffixStyle = null;

	/// An icon to show before the input field.
	///
	/// The size and color of the icon is configured automatically using an
	/// [IconTheme] and therefore does not need to be explicitly given in the
	/// icon widget.
	///
	/// See [Icon], [ImageIcon].
	final Widget icon;

	/// Text that describes the input field.
	///
	/// When the input field is empty and unfocused, the label is displayed on
	/// top of the input field (i.e., at the same location on the screen where
	/// text my be entered in the input field). When the input field receives
	/// focus (or if the field is non-empty), the label moves above (i.e.,
	/// vertically adjacent to) the input field.
	final String labelText;

	/// The style to use for the [labelText] when the label is above (i.e.,
	/// vertically adjacent to) the input field.
	///
	/// When the [labelText] is on top of the input field, the text uses the
	/// [hintStyle] instead.
	///
	/// If null, defaults of a value derived from the base [TextStyle] for the
	/// input field and the current [Theme].
	final TextStyle labelStyle;

	/// Text that provides context about the field’s value, such as how the value
	/// will be used.
	///
	/// If non-null, the text is displayed below the input field, in the same
	/// location as [errorText]. If a non-null [errorText] value is specified then
	/// the helper text is not shown.
	final String helperText;

	/// The style to use for the [helperText].
	final TextStyle helperStyle;

	/// Text that suggests what sort of input the field accepts.
	///
	/// Displayed on top of the input field (i.e., at the same location on the
	/// screen where text my be entered in the input field) when the input field
	/// is empty and either (a) [labelText] is null or (b) the input field has
	/// focus.
	final String hintText;

	/// The style to use for the [hintText].
	///
	/// Also used for the [labelText] when the [labelText] is displayed on
	/// top of the input field (i.e., at the same location on the screen where
	/// text my be entered in the input field).
	///
	/// If null, defaults of a value derived from the base [TextStyle] for the
	/// input field and the current [Theme].
	final TextStyle hintStyle;

	/// Text that appears below the input field.
	///
	/// If non-null, the divider that appears below the input field is red.
	final String errorText;

	/// The style to use for the [errorText].
	///
	/// If null, defaults of a value derived from the base [TextStyle] for the
	/// input field and the current [Theme].
	final TextStyle errorStyle;

	/// Whether the input field is part of a dense form (i.e., uses less vertical
	/// space).
	///
	/// Defaults to false.
	final bool isDense;

	/// Whether the decoration is the same size as the input field.
	///
	/// A collapsed decoration cannot have [labelText], [errorText], an [icon], or
	/// a divider because those elements require extra space.
	///
	/// To create a collapsed input decoration, use [InputDecoration..collapsed].
	final bool isCollapsed;

	/// Whether to hide the divider below the input field and above the error text.
	///
	/// Defaults to false.
	final bool hideDivider;

	/// Optional text prefix to place on the line before the input.
	///
	/// Uses the [prefixStyle]. Uses [hintStyle] if [prefixStyle] isn't
	/// specified. Prefix is not returned as part of the input.
	final String prefixText;

	/// The style to use for the [prefixText].
	///
	/// If null, defaults to the [hintStyle].
	final TextStyle prefixStyle;

	/// Optional text suffix to place on the line after the input.
	///
	/// Uses the [suffixStyle]. Uses [hintStyle] if [suffixStyle] isn't
	/// specified. Suffix is not returned as part of the input.
	final String suffixText;

	/// The style to use for the [suffixText].
	///
	/// If null, defaults to the [hintStyle].
	final TextStyle suffixStyle;

	/// Creates a copy of this input decoration but with the given fields replaced
	/// with the new values.
	///
	/// Always sets [isCollapsed] to false.
	InputDecoration copyWith({
	Widget icon,
	String labelText,
	TextStyle labelStyle,
	String helperText,
	TextStyle helperStyle,
	String hintText,
	TextStyle hintStyle,
	String errorText,
	TextStyle errorStyle,
	bool isDense,
	bool hideDivider,
	String prefixText,
	TextStyle prefixStyle,
	String suffixText,
	TextStyle suffixStyle,
	}) {
	return new InputDecoration(
	icon: icon ?? this.icon,
	labelText: labelText ?? this.labelText,
	labelStyle: labelStyle ?? this.labelStyle,
	helperText: helperText ?? this.helperText,
	helperStyle: helperStyle ?? this.helperStyle,
	hintText: hintText ?? this.hintText,
	hintStyle: hintStyle ?? this.hintStyle,
	errorText: errorText ?? this.errorText,
	errorStyle: errorStyle ?? this.errorStyle,
	isDense: isDense ?? this.isDense,
	hideDivider: hideDivider ?? this.hideDivider,
	prefixText: prefixText ?? this.prefixText,
	prefixStyle: prefixStyle ?? this.prefixStyle,
	suffixText: suffixText ?? this.suffixText,
	suffixStyle: suffixStyle ?? this.suffixStyle,
	);
	}

	@override
	bool operator ==(dynamic other) {
	if (identical(this, other))
	return true;
	if (other.runtimeType != runtimeType)
	return false;
	final InputDecoration typedOther = other;
	return typedOther.icon == icon
	&& typedOther.labelText == labelText
	&& typedOther.labelStyle == labelStyle
	&& typedOther.helperText == helperText
	&& typedOther.helperStyle == helperStyle
	&& typedOther.hintText == hintText
	&& typedOther.hintStyle == hintStyle
	&& typedOther.errorText == errorText
	&& typedOther.errorStyle == errorStyle
	&& typedOther.isDense == isDense
	&& typedOther.isCollapsed == isCollapsed
	&& typedOther.hideDivider == hideDivider
	&& typedOther.prefixText == prefixText
	&& typedOther.prefixStyle == prefixStyle
	&& typedOther.suffixText == suffixText
	&& typedOther.suffixStyle == suffixStyle;
	}

	@override
	int get hashCode {
	return hashValues(
	icon,
	labelText,
	labelStyle,
	helperText,
	helperStyle,
	hintText,
	hintStyle,
	errorText,
	errorStyle,
	isDense,
	isCollapsed,
	hideDivider,
	prefixText,
	prefixStyle,
	suffixText,
	suffixStyle,
	);
	}

	@override
	String toString() {
	final List<String> description = <String>[];
	if (icon != null)
	description.add('icon: $icon');
	if (labelText != null)
	description.add('labelText: "$labelText"');
	if (helperText != null)
	description.add('helperText: "$helperText"');
	if (hintText != null)
	description.add('hintText: "$hintText"');
	if (errorText != null)
	description.add('errorText: "$errorText"');
	if (isDense)
	description.add('isDense: $isDense');
	if (isCollapsed)
	description.add('isCollapsed: $isCollapsed');
	if (hideDivider)
	description.add('hideDivider: $hideDivider');
	if (prefixText != null)
	description.add('prefixText: $prefixText');
	if (prefixStyle != null)
	description.add('prefixStyle: $prefixStyle');
	if (suffixText != null)
	description.add('suffixText: $suffixText');
	if (suffixStyle != null)
	description.add('suffixStyle: $suffixStyle');
	return 'InputDecoration(${description.join(', ')})';
	}
	}

	/// Displays the visual elements of a Material Design text field around an
	/// arbitrary widget.
	///
	/// Use [InputDecorator] to create widgets that look and behave like a
	/// [TextField] but can be used to input information other than text.
	///
	/// The configuration of this widget is primarily provided in the form of an
	/// [InputDecoration] object.
	///
	/// Requires one of its ancestors to be a [Material] widget.
	///
	/// See also:
	///
	/// * [TextField], which uses an [InputDecorator] to draw labels and other
	/// visual elements around a text entry widget.
	/// * [Decoration] and [DecoratedBox], for drawing arbitrary decorations
	/// around other widgets.
	class InputDecorator extends StatelessWidget {
	/// Creates a widget that displayes labels and other visual elements similar
	/// to a [TextField].
	///
	/// The [isFocused] and [isEmpty] arguments must not be null.
	const InputDecorator({
	Key key,
	@required this.decoration,
	this.baseStyle,
	this.textAlign,
	this.isFocused: false,
	this.isEmpty: false,
	this.child,
	}) : assert(isFocused != null),
	assert(isEmpty != null),
	super(key: key);

	/// The text and styles to use when decorating the child.
	final InputDecoration decoration;

	/// The style on which to base the label, hint, and error styles if the
	/// [decoration] does not provide explicit styles.
	///
	/// If null, defaults to a text style from the current [Theme].
	final TextStyle baseStyle;

	/// How the text in the decoration should be aligned horizontally.
	final TextAlign textAlign;

	/// Whether the input field has focus.
	///
	/// Determines the position of the label text and the color of the divider.
	///
	/// Defaults to false.
	final bool isFocused;

	/// Whether the input field is empty.
	///
	/// Determines the position of the label text and whether to display the hint
	/// text.
	///
	/// Defaults to false.
	final bool isEmpty;

	/// The widget below this widget in the tree.
	final Widget child;

	@override
	void debugFillProperties(DiagnosticPropertiesBuilder description) {
	super.debugFillProperties(description);
	description.add(new DiagnosticsProperty<InputDecoration>('decoration', decoration));
	description.add(new EnumProperty<TextStyle>('baseStyle', baseStyle));
	description.add(new DiagnosticsProperty<bool>('isFocused', isFocused));
	description.add(new DiagnosticsProperty<bool>('isEmpty', isEmpty));
	}

	Color _getActiveColor(ThemeData themeData) {
	if (isFocused) {
	switch (themeData.brightness) {
	case Brightness.dark:
	return themeData.accentColor;
	case Brightness.light:
	return themeData.primaryColor;
	}
	}
	return themeData.hintColor;
	}

	Widget _buildContent(Color borderColor, double topPadding, bool isDense, Widget inputChild) {
	final double bottomPadding = isDense ? 8.0 : 1.0;
	const double bottomBorder = 2.0;
	final double bottomHeight = isDense ? 14.0 : 18.0;

	final EdgeInsets padding = new EdgeInsets.only(top: topPadding, bottom: bottomPadding);
	final EdgeInsets margin = new EdgeInsets.only(bottom: bottomHeight - (bottomPadding + bottomBorder));

	if (decoration.hideDivider) {
	return new Container(
	margin: margin + const EdgeInsets.only(bottom: bottomBorder),
	padding: padding,
	child: inputChild,
	);
	}

	return new AnimatedContainer(
	margin: margin,
	padding: padding,
	duration: _kTransitionDuration,
	curve: _kTransitionCurve,
	decoration: new BoxDecoration(
	border: new Border(
	bottom: new BorderSide(
	color: borderColor,
	width: bottomBorder,
	),
	),
	),
	child: inputChild,
	);
	}

	@override
	Widget build(BuildContext context) {
	assert(debugCheckHasMaterial(context));
	final ThemeData themeData = Theme.of(context);

	final bool isDense = decoration.isDense;
	final bool isCollapsed = decoration.isCollapsed;
	assert(!isDense \|\| !isCollapsed);

	final String labelText = decoration.labelText;
	final String helperText = decoration.helperText;
	final String hintText = decoration.hintText;
	final String errorText = decoration.errorText;

	final TextStyle baseStyle = this.baseStyle ?? themeData.textTheme.subhead;
	final TextStyle hintStyle = decoration.hintStyle ?? baseStyle.copyWith(color: themeData.hintColor);

	final Color activeColor = _getActiveColor(themeData);

	double topPadding = isCollapsed ? 0.0 : (isDense ? 12.0 : 16.0);

	final List<Widget> stackChildren = <Widget>[];

	// If we're not focused, there's no value, and labelText was provided,
	// then the label appears where the hint would. And we will not show
	// the hintText.
	final bool hasInlineLabel = !isFocused && labelText != null && isEmpty;

	if (labelText != null) {
	assert(!isCollapsed);
	final TextStyle labelStyle = hasInlineLabel ?
	hintStyle : (decoration.labelStyle ?? themeData.textTheme.caption.copyWith(color: activeColor));

	final double topPaddingIncrement = themeData.textTheme.caption.fontSize + (isDense ? 4.0 : 8.0);
	double top = topPadding;
	if (hasInlineLabel)
	top += topPaddingIncrement + baseStyle.fontSize - labelStyle.fontSize;

	stackChildren.add(
	new AnimatedPositioned(
	left: 0.0,
	top: top,
	duration: _kTransitionDuration,
	curve: _kTransitionCurve,
	child: new _AnimatedLabel(
	text: labelText,
	style: labelStyle,
	duration: _kTransitionDuration,
	curve: _kTransitionCurve,
	),
	),
	);

	topPadding += topPaddingIncrement;
	}

	if (hintText != null) {
	stackChildren.add(
	new Positioned(
	left: 0.0,
	right: 0.0,
	top: topPadding + baseStyle.fontSize - hintStyle.fontSize,
	child: new AnimatedOpacity(
	opacity: (isEmpty && !hasInlineLabel) ? 1.0 : 0.0,
	duration: _kTransitionDuration,
	curve: _kTransitionCurve,
	child: new Text(
	hintText,
	style: hintStyle,
	overflow: TextOverflow.ellipsis,
	textAlign: textAlign,
	),
	),
	),
	);
	}

	Widget inputChild = new KeyedSubtree(
	// It's important that we maintain the state of our child subtree, as it
	// may be stateful (e.g. containing text selections). Since our build
	// function risks changing the depth of the tree, we preserve the subtree
	// using global keys.
	// GlobalObjectKey(context) will always be the same whenever we are built.
	// Additionally, we use a subclass of GlobalObjectKey to avoid clashes
	// with anyone else using our BuildContext as their global object key
	// value.
	key: new _InputDecoratorChildGlobalKey(context),
	child: child,
	);

	if (!hasInlineLabel && (!isEmpty \|\| hintText == null) &&
	(decoration?.prefixText != null \|\| decoration?.suffixText != null)) {
	final List<Widget> rowContents = <Widget>[];
	if (decoration.prefixText != null) {
	rowContents.add(
	new Text(decoration.prefixText,
	style: decoration.prefixStyle ?? hintStyle)
	);
	}
	rowContents.add(new Expanded(child: inputChild));
	if (decoration.suffixText != null) {
	rowContents.add(
	new Text(decoration.suffixText,
	style: decoration.suffixStyle ?? hintStyle)
	);
	}
	inputChild = new Row(children: rowContents);
	}

	if (isCollapsed) {
	stackChildren.add(inputChild);
	} else {
	final Color borderColor = errorText == null ? activeColor : themeData.errorColor;
	stackChildren.add(_buildContent(borderColor, topPadding, isDense, inputChild));
	}

	if (!isDense && (errorText != null \|\| helperText != null)) {
	assert(!isCollapsed);
	final TextStyle captionStyle = themeData.textTheme.caption;
	final TextStyle subtextStyle = errorText != null
	? decoration.errorStyle ?? captionStyle.copyWith(color: themeData.errorColor)
	: decoration.helperStyle ?? captionStyle.copyWith(color: themeData.hintColor);

	stackChildren.add(new Positioned(
	left: 0.0,
	right: 0.0,
	bottom: 0.0,
	child: new Text(
	errorText ?? helperText,
	style: subtextStyle,
	textAlign: textAlign,
	overflow: TextOverflow.ellipsis,
	),
	));
	}

	final Widget stack = new Stack(
	fit: StackFit.passthrough,
	children: stackChildren
	);

	if (decoration.icon != null) {
	assert(!isCollapsed);
	final double iconSize = isDense ? 18.0 : 24.0;
	final double iconTop = topPadding + (baseStyle.fontSize - iconSize) / 2.0;
	return new Row(
	crossAxisAlignment: CrossAxisAlignment.start,
	children: <Widget>[
	new Container(
	margin: new EdgeInsets.only(top: iconTop),
	width: isDense ? 40.0 : 48.0,
	child: IconTheme.merge(
	data: new IconThemeData(
	color: isFocused ? activeColor : Colors.black45,
	size: isDense ? 18.0 : 24.0,
	),
	child: decoration.icon,
	),
	),
	new Expanded(child: stack),
	],
	);
	} else {
	return new ConstrainedBox(
	constraints: const BoxConstraints(minWidth: double.INFINITY),
	child: stack,
	);
	}
	}
	}

	// Smoothly animate the label of an InputDecorator as the label
	// transitions between inline and caption.
	class _AnimatedLabel extends ImplicitlyAnimatedWidget {
	const _AnimatedLabel({
	Key key,
	this.text,
	@required this.style,
	Curve curve: Curves.linear,
	@required Duration duration,
	}) : assert(style != null),
	super(key: key, curve: curve, duration: duration);

	final String text;
	final TextStyle style;

	@override
	_AnimatedLabelState createState() => new _AnimatedLabelState();

	@override
	void debugFillProperties(DiagnosticPropertiesBuilder description) {
	super.debugFillProperties(description);
	style?.debugFillProperties(description);
	}
	}

	class _AnimatedLabelState extends AnimatedWidgetBaseState<_AnimatedLabel> {
	TextStyleTween _style;

	@override
	void forEachTween(TweenVisitor<dynamic> visitor) {
	_style = visitor(_style, widget.style, (dynamic value) => new TextStyleTween(begin: value));
	}

	@override
	Widget build(BuildContext context) {
	TextStyle style = _style.evaluate(animation);
	double scale = 1.0;
	if (style.fontSize != widget.style.fontSize) {
	// While the fontSize is transitioning, use a scaled Transform as a
	// fraction of the original fontSize. That way we get a smooth scaling
	// effect with no snapping between discrete font sizes.
	scale = style.fontSize / widget.style.fontSize;
	style = style.copyWith(fontSize: widget.style.fontSize);
	}

	return new Transform(
	transform: new Matrix4.identity()..scale(scale),
	child: new Text(
	widget.text,
	style: style,
	),
	);
	}
	}