packages/flutter/lib/src/material/raised_button.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/foundation.dart';
import 'package:flutter/widgets.dart';

import 'button.dart';
import 'colors.dart';
import 'theme.dart';

/// A material design "raised button".
///
/// A raised button consists of a rectangular piece of material that hovers over
/// the interface.
///
/// Use raised buttons to add dimension to otherwise mostly flat layouts, e.g.
/// in long busy lists of content, or in wide spaces. Avoid using raised buttons
/// on already-raised content such as dialogs or cards.
///
/// If the [onPressed] callback is null, then the button will be disabled and by
/// default will appear like a flat button in the [disabledColor]. If you are
/// trying to change the button's [color] and it is not having any effect, check
/// that you are passing a non-null [onPressed] handler.
///
/// Requires one of its ancestors to be a [Material] widget.
///
/// If you want an ink-splash effect for taps, but don't want to use a button,
/// consider using [InkWell] directly.
///
/// Raised buttons will expand to fit the child widget, if necessary.
///
/// See also:
///
///  * [FlatButton], a material design button without a shadow.
///  * [DropdownButton], a button that shows options to select from.
///  * [FloatingActionButton], the round button in material applications.
///  * [IconButton], to create buttons that just contain icons.
///  * [InkWell], which implements the ink splash part of a flat button.
///  * <https://material.google.com/components/buttons.html>
class RaisedButton extends StatelessWidget {
  /// Creates a raised button.
  ///
  /// The [child] argument is required and is typically a [Text] widget in all
  /// caps.
  const RaisedButton({
    Key key,
    @required this.onPressed,
    this.color,
    this.highlightColor,
    this.splashColor,
    this.disabledColor,
    this.elevation: 2.0,
    this.highlightElevation: 8.0,
    this.disabledElevation: 0.0,
    this.colorBrightness,
    this.child
  }) : super(key: key);

  /// The callback that is called when the button is tapped or otherwise
  /// activated.
  ///
  /// If this is set to null, the button will be disabled.
  final VoidCallback onPressed;

  /// The primary color of the button, as printed on the [Material], while it
  /// is in its default (unpressed, enabled) state.
  ///
  /// Defaults to null, meaning that the color is automatically derived from the
  /// [Theme].
  ///
  /// Typically, a material design color will be used, as follows:
  ///
  /// ```dart
  ///  new RaisedButton(
  ///    color: Colors.blue,
  ///    onPressed: _handleTap,
  ///    child: new Text('DEMO'),
  ///  ),
  /// ```
  final Color color;

  /// The primary color of the button when the button is in the down (pressed)
  /// state.
  ///
  /// The splash is represented as a circular overlay that appears above the
  /// [highlightColor] overlay. The splash overlay has a center point that
  /// matches the hit point of the user touch event. The splash overlay will
  /// expand to fill the button area if the touch is held for long enough time.
  /// If the splash color has transparency then the highlight and button color
  /// will show through.
  ///
  /// Defaults to the splash color from the [Theme].
  final Color splashColor;

  /// The secondary color of the button when the button is in the down (pressed)
  /// state.
  ///
  /// The highlight color is represented as a solid color that is overlaid over
  /// the button color (if any). If the highlight color has transparency, the
  /// button color will show through. The highlight fades in quickly as the
  /// button is held down.
  ///
  /// Defaults to the highlight color from the [Theme].
  final Color highlightColor;


  /// The color of the button when the button is disabled. Buttons are disabled
  /// by default.
  ///
  /// To enable a button, set its [onPressed] property to a non-null value.
  final Color disabledColor;

  /// The z-coordinate at which to place this button. This controls the size of
  /// the shadow below the raised button.
  ///
  /// Defaults to 2, the appropriate elevation for raised buttons.
  ///
  /// See also:
  ///
  ///  * [FlatButton], a button with no elevation.
  final double elevation;

  /// The z-coordinate at which to place this button when highlighted. This
  /// controls the size of the shadow below the raised button.
  ///
  /// Defaults to 8, the appropriate elevation for raised buttons while they are
  /// being touched.
  ///
  /// See also:
  ///
  ///  * [elevation], the default elevation.
  final double highlightElevation;

  /// The z-coordinate at which to place this button when disabled. This
  /// controls the size of the shadow below the raised button.
  ///
  /// Defaults to 0, the appropriate elevation for disabled raised buttons.
  ///
  /// See also:
  ///
  ///  * [elevation], the default elevation.
  final double disabledElevation;

  /// The theme brightness to use for this button.
  ///
  /// Defaults to the brightness from [ThemeData.brightness].
  final Brightness colorBrightness;

  /// The widget below this widget in the tree.
  ///
  /// Typically a [Text] widget in all caps.
  final Widget child;

  /// Whether the button is enabled or disabled.
  ///
  /// Buttons are disabled by default. To enable a button, set its [onPressed]
  /// property to a non-null value.
  bool get enabled => onPressed != null;

  Color _getColor(BuildContext context) {
    if (enabled) {
      return color ?? Theme.of(context).buttonColor;
    } else {
      if (disabledColor != null)
        return disabledColor;
      final Brightness brightness = Theme.of(context).brightness;
      assert(brightness != null);
      switch (brightness) {
        case Brightness.light:
          return Colors.black12;
        case Brightness.dark:
          return Colors.white12;
      }
      return null;
    }
  }

  @override
  Widget build(BuildContext context) {
    return new MaterialButton(
      onPressed: onPressed,
      color: _getColor(context),
      highlightColor: highlightColor ?? Theme.of(context).highlightColor,
      splashColor: splashColor ?? Theme.of(context).splashColor,
      elevation: enabled ? elevation : disabledElevation,
      highlightElevation: enabled ? highlightElevation : disabledElevation,
      colorBrightness: colorBrightness,
      child: child,
    );
  }
}