packages/flutter/lib/src/widgets/icon.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/rendering.dart';

import 'basic.dart';
import 'debug.dart';
import 'framework.dart';
import 'icon_data.dart';
import 'icon_theme.dart';
import 'icon_theme_data.dart';

/// A graphical icon widget drawn with a glyph from a font described in
/// an [IconData] such as material's predefined [IconData]s in [Icons].
///
/// Icons are not interactive. For an interactive icon, consider material's
/// [IconButton].
///
/// There must be an ambient [Directionality] widget when using [Icon].
/// Typically this is introduced automatically by the [WidgetsApp] or
/// [MaterialApp].
///
/// See also:
///
///  * [IconButton], for interactive icons.
///  * [Icons], for the list of available icons for use with this class.
///  * [IconTheme], which provides ambient configuration for icons.
///  * [ImageIcon], for showing icons from [AssetImage]s or other [ImageProvider]s.
class Icon extends StatelessWidget {
  /// Creates an icon.
  ///
  /// The [size] and [color] default to the value given by the current [IconTheme].
  const Icon(this.icon, {
    Key key,
    this.size,
    this.color,
    this.semanticLabel,
    this.textDirection,
  }) : super(key: key);

  /// The icon to display. The available icons are described in [Icons].
  ///
  /// The icon can be null, in which case the widget will render as an empty
  /// space of the specified [size].
  final IconData icon;

  /// The size of the icon in logical pixels.
  ///
  /// Icons occupy a square with width and height equal to size.
  ///
  /// Defaults to the current [IconTheme] size, if any. If there is no
  /// [IconTheme], or it does not specify an explicit size, then it defaults to
  /// 24.0.
  ///
  /// If this [Icon] is being placed inside an [IconButton], then use
  /// [IconButton.iconSize] instead, so that the [IconButton] can make the splash
  /// area the appropriate size as well. The [IconButton] uses an [IconTheme] to
  /// pass down the size to the [Icon].
  final double size;

  /// The color to use when drawing the icon.
  ///
  /// Defaults to the current [IconTheme] color, if any.
  ///
  /// The given color will be adjusted by the opacity of the current
  /// [IconTheme], if any.
  ///
  ///
  /// In material apps, if there is a [Theme] without any [IconTheme]s
  /// specified, icon colors default to white if the theme is dark
  /// and black if the theme is light.
  ///
  /// If no [IconTheme] and no [Theme] is specified, icons will default to black.
  ///
  /// See [Theme] to set the current theme and [ThemeData.brightness]
  /// for setting the current theme's brightness.
  ///
  /// Typically, a material design color will be used, as follows:
  ///
  /// ```dart
  ///  new Icon(
  ///    icon: Icons.widgets,
  ///    color: Colors.blue.shade400,
  ///  ),
  /// ```
  final Color color;

  /// Semantic label for the icon.
  ///
  /// Announced in accessibility modes (e.g TalkBack/VoiceOver).
  /// This label does not show in the UI.
  ///
  /// See also:
  ///
  ///  * [Semantics.label], which is set to [semanticLabel] in the underlying
  ///    [Semantics] widget.
  final String semanticLabel;

  /// The text direction to use for rendering the icon.
  ///
  /// If this is null, the ambient [Directionality] is used instead.
  ///
  /// Some icons follow the reading direction. For example, "back" buttons point
  /// left in left-to-right environments and right in right-to-left
  /// environments. Such icons have their [IconData.matchTextDirection] field
  /// set to true, and the [Icon] widget uses the [textDirection] to determine
  /// the orientation in which to draw the icon.
  ///
  /// This property has no effect if the [icon]'s [IconData.matchTextDirection]
  /// field is false, but for consistency a text direction value must always be
  /// specified, either directly using this property or using [Directionality].
  final TextDirection textDirection;

  @override
  Widget build(BuildContext context) {
    assert(this.textDirection != null || debugCheckHasDirectionality(context));
    final TextDirection textDirection = this.textDirection ?? Directionality.of(context);

    final IconThemeData iconTheme = IconTheme.of(context);

    final double iconSize = size ?? iconTheme.size;

    if (icon == null) {
      return new Semantics(
        label: semanticLabel,
        child: new SizedBox(width: iconSize, height: iconSize)
      );
    }

    final double iconOpacity = iconTheme.opacity;
    Color iconColor = color ?? iconTheme.color;
    if (iconOpacity != 1.0)
      iconColor = iconColor.withOpacity(iconColor.opacity * iconOpacity);

    Widget iconWidget = new RichText(
      textDirection: textDirection, // Since we already fetched it for the assert...
      text: new TextSpan(
        text: new String.fromCharCode(icon.codePoint),
        style: new TextStyle(
          inherit: false,
          color: iconColor,
          fontSize: iconSize,
          fontFamily: icon.fontFamily,
          package: icon.fontPackage,
        ),
      ),
    );

    if (icon.matchTextDirection) {
      switch (textDirection) {
        case TextDirection.rtl:
          iconWidget = new Transform(
            transform: new Matrix4.identity()..scale(-1.0, 1.0, 1.0),
            alignment: Alignment.center,
            transformHitTests: false,
            child: iconWidget,
          );
          break;
        case TextDirection.ltr:
          break;
      }
    }

    return new Semantics(
      label: semanticLabel,
      child: new ExcludeSemantics(
        child: new SizedBox(
          width: iconSize,
          height: iconSize,
          child: new Center(
            child: iconWidget,
          ),
        ),
      ),
    );
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(new DiagnosticsProperty<IconData>('icon', icon, ifNull: '<empty>', showName: false));
    properties.add(new DoubleProperty('size', size, defaultValue: null));
    properties.add(new DiagnosticsProperty<Color>('color', color, defaultValue: null));
  }
}