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 'dart:math' as math;

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

import 'button_theme.dart';
import 'constants.dart';
import 'ink_well.dart';
import 'material.dart';
import 'material_state.dart';
import 'theme.dart';
import 'theme_data.dart';

/// Creates a button based on [Semantics], [Material], and [InkWell]
/// widgets.
///
/// This class does not use the current [Theme] or [ButtonTheme] to
/// compute default values for unspecified parameters. It's intended to
/// be used for custom Material buttons that optionally incorporate defaults
/// from the themes or from app-specific sources.
///
/// [RaisedButton] and [FlatButton] configure a [RawMaterialButton] based
/// on the current [Theme] and [ButtonTheme].
class RawMaterialButton extends StatefulWidget {
  /// Create a button based on [Semantics], [Material], and [InkWell] widgets.
  ///
  /// The [shape], [elevation], [focusElevation], [hoverElevation],
  /// [highlightElevation], [disabledElevation], [padding], [constraints],
  /// [autofocus], and [clipBehavior] arguments must not be null. Additionally,
  /// [elevation], [focusElevation], [hoverElevation], [highlightElevation], and
  /// [disabledElevation] must be non-negative.
  const RawMaterialButton({
    Key key,
    @required this.onPressed,
    this.onHighlightChanged,
    this.textStyle,
    this.fillColor,
    this.focusColor,
    this.hoverColor,
    this.highlightColor,
    this.splashColor,
    this.elevation = 2.0,
    this.focusElevation = 4.0,
    this.hoverElevation = 4.0,
    this.highlightElevation = 8.0,
    this.disabledElevation = 0.0,
    this.padding = EdgeInsets.zero,
    this.constraints = const BoxConstraints(minWidth: 88.0, minHeight: 36.0),
    this.shape = const RoundedRectangleBorder(),
    this.animationDuration = kThemeChangeDuration,
    this.clipBehavior = Clip.none,
    this.focusNode,
    this.autofocus = false,
    MaterialTapTargetSize materialTapTargetSize,
    this.child,
  }) : materialTapTargetSize = materialTapTargetSize ?? MaterialTapTargetSize.padded,
       assert(shape != null),
       assert(elevation != null && elevation >= 0.0),
       assert(focusElevation != null && focusElevation >= 0.0),
       assert(hoverElevation != null && hoverElevation >= 0.0),
       assert(highlightElevation != null && highlightElevation >= 0.0),
       assert(disabledElevation != null && disabledElevation >= 0.0),
       assert(padding != null),
       assert(constraints != null),
       assert(animationDuration != null),
       assert(clipBehavior != null),
       assert(autofocus != null),
       super(key: key);

  /// Called when the button is tapped or otherwise activated.
  ///
  /// If this is set to null, the button will be disabled, see [enabled].
  final VoidCallback onPressed;

  /// Called by the underlying [InkWell] widget's [InkWell.onHighlightChanged]
  /// callback.
  ///
  /// If [onPressed] changes from null to non-null while a gesture is ongoing,
  /// this can fire during the build phase (in which case calling
  /// [State.setState] is not allowed).
  final ValueChanged<bool> onHighlightChanged;

  /// Defines the default text style, with [Material.textStyle], for the
  /// button's [child].
  ///
  /// If [textStyle.color] is a [MaterialStateProperty<Color>], [MaterialStateProperty.resolve]
  /// is used for the following [MaterialState]s:
  ///
  ///  * [MaterialState.pressed].
  ///  * [MaterialState.hovered].
  ///  * [MaterialState.focused].
  ///  * [MaterialState.disabled].
  final TextStyle textStyle;

  /// The color of the button's [Material].
  final Color fillColor;

  /// The color for the button's [Material] when it has the input focus.
  final Color focusColor;

  /// The color for the button's [Material] when a pointer is hovering over it.
  final Color hoverColor;

  /// The highlight color for the button's [InkWell].
  final Color highlightColor;

  /// The splash color for the button's [InkWell].
  final Color splashColor;

  /// The elevation for the button's [Material] when the button
  /// is [enabled] but not pressed.
  ///
  /// Defaults to 2.0. The value is always non-negative.
  ///
  /// See also:
  ///
  ///  * [highlightElevation], the default elevation.
  ///  * [hoverElevation], the elevation when a pointer is hovering over the
  ///    button.
  ///  * [focusElevation], the elevation when the button is focused.
  ///  * [disabledElevation], the elevation when the button is disabled.
  final double elevation;

  /// The elevation for the button's [Material] when the button
  /// is [enabled] and a pointer is hovering over it.
  ///
  /// Defaults to 4.0. The value is always non-negative.
  ///
  /// If the button is [enabled], and being pressed (in the highlighted state),
  /// then the [highlightElevation] take precedence over the [hoverElevation].
  ///
  /// See also:
  ///
  ///  * [elevation], the default elevation.
  ///  * [focusElevation], the elevation when the button is focused.
  ///  * [disabledElevation], the elevation when the button is disabled.
  ///  * [highlightElevation], the elevation when the button is pressed.
  final double hoverElevation;

  /// The elevation for the button's [Material] when the button
  /// is [enabled] and has the input focus.
  ///
  /// Defaults to 4.0. The value is always non-negative.
  ///
  /// If the button is [enabled], and being pressed (in the highlighted state),
  /// or a mouse cursor is hovering over the button, then the [hoverElevation]
  /// and [highlightElevation] take precedence over the [focusElevation].
  ///
  /// See also:
  ///
  ///  * [elevation], the default elevation.
  ///  * [hoverElevation], the elevation when a pointer is hovering over the
  ///    button.
  ///  * [disabledElevation], the elevation when the button is disabled.
  ///  * [highlightElevation], the elevation when the button is pressed.
  final double focusElevation;

  /// The elevation for the button's [Material] when the button
  /// is [enabled] and pressed.
  ///
  /// Defaults to 8.0. The value is always non-negative.
  ///
  /// See also:
  ///
  ///  * [elevation], the default elevation.
  ///  * [hoverElevation], the elevation when a pointer is hovering over the
  ///  button.
  ///  * [focusElevation], the elevation when the button is focused.
  ///  * [disabledElevation], the elevation when the button is disabled.
  final double highlightElevation;

  /// The elevation for the button's [Material] when the button
  /// is not [enabled].
  ///
  /// Defaults to 0.0. The value is always non-negative.
  ///
  /// See also:
  ///
  ///  * [elevation], the default elevation.
  ///  * [hoverElevation], the elevation when a pointer is hovering over the
  ///  button.
  ///  * [focusElevation], the elevation when the button is focused.
  ///  * [highlightElevation], the elevation when the button is pressed.
  final double disabledElevation;

  /// The internal padding for the button's [child].
  final EdgeInsetsGeometry padding;

  /// Defines the button's size.
  ///
  /// Typically used to constrain the button's minimum size.
  final BoxConstraints constraints;

  /// The shape of the button's [Material].
  ///
  /// The button's highlight and splash are clipped to this shape. If the
  /// button has an elevation, then its drop shadow is defined by this shape.
  ///
  /// If [shape] is a [MaterialStateProperty<ShapeBorder>], [MaterialStateProperty.resolve]
  /// is used for the following [MaterialState]s:
  ///
  /// * [MaterialState.pressed].
  /// * [MaterialState.hovered].
  /// * [MaterialState.focused].
  /// * [MaterialState.disabled].
  final ShapeBorder shape;

  /// Defines the duration of animated changes for [shape] and [elevation].
  ///
  /// The default value is [kThemeChangeDuration].
  final Duration animationDuration;

  /// Typically the button's label.
  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;

  /// Configures the minimum size of the tap target.
  ///
  /// Defaults to [MaterialTapTargetSize.padded].
  ///
  /// See also:
  ///
  ///  * [MaterialTapTargetSize], for a description of how this affects tap targets.
  final MaterialTapTargetSize materialTapTargetSize;

  /// {@macro flutter.widgets.Focus.focusNode}
  final FocusNode focusNode;

  /// {@macro flutter.widgets.Focus.autofocus}
  final bool autofocus;

  /// {@macro flutter.widgets.Clip}
  ///
  /// Defaults to [Clip.none], and must not be null.
  final Clip clipBehavior;

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

class _RawMaterialButtonState extends State<RawMaterialButton> {
  final Set<MaterialState> _states = <MaterialState>{};

  bool get _hovered => _states.contains(MaterialState.hovered);
  bool get _focused => _states.contains(MaterialState.focused);
  bool get _pressed => _states.contains(MaterialState.pressed);
  bool get _disabled => _states.contains(MaterialState.disabled);

  void _updateState(MaterialState state, bool value) {
    value ? _states.add(state) : _states.remove(state);
  }

  void _handleHighlightChanged(bool value) {
    if (_pressed != value) {
      setState(() {
        _updateState(MaterialState.pressed, value);
        if (widget.onHighlightChanged != null) {
          widget.onHighlightChanged(value);
        }
      });
    }
  }

  void _handleHoveredChanged(bool value) {
    if (_hovered != value) {
      setState(() {
        _updateState(MaterialState.hovered, value);
      });
    }
  }

  void _handleFocusedChanged(bool value) {
    if (_focused != value) {
      setState(() {
        _updateState(MaterialState.focused, value);
      });
    }
  }

  @override
  void initState() {
    super.initState();
    _updateState(MaterialState.disabled, !widget.enabled);
  }

  @override
  void didUpdateWidget(RawMaterialButton oldWidget) {
    super.didUpdateWidget(oldWidget);
    _updateState(MaterialState.disabled, !widget.enabled);
    // If the button is disabled while a press gesture is currently ongoing,
    // InkWell makes a call to handleHighlightChanged. This causes an exception
    // because it calls setState in the middle of a build. To preempt this, we
    // manually update pressed to false when this situation occurs.
    if (_disabled && _pressed) {
      _handleHighlightChanged(false);
    }
  }

  double get _effectiveElevation {
    // These conditionals are in order of precedence, so be careful about
    // reorganizing them.
    if (_disabled) {
      return widget.disabledElevation;
    }
    if (_pressed) {
      return widget.highlightElevation;
    }
    if (_hovered) {
      return widget.hoverElevation;
    }
    if (_focused) {
      return widget.focusElevation;
    }
    return widget.elevation;
  }

  @override
  Widget build(BuildContext context) {
    final Color effectiveTextColor = MaterialStateProperty.resolveAs<Color>(widget.textStyle?.color, _states);
    final ShapeBorder effectiveShape =  MaterialStateProperty.resolveAs<ShapeBorder>(widget.shape, _states);

    final Widget result = ConstrainedBox(
      constraints: widget.constraints,
      child: Material(
        elevation: _effectiveElevation,
        textStyle: widget.textStyle?.copyWith(color: effectiveTextColor),
        shape: effectiveShape,
        color: widget.fillColor,
        type: widget.fillColor == null ? MaterialType.transparency : MaterialType.button,
        animationDuration: widget.animationDuration,
        clipBehavior: widget.clipBehavior,
        child: InkWell(
          focusNode: widget.focusNode,
          canRequestFocus: widget.enabled,
          onFocusChange: _handleFocusedChanged,
          autofocus: widget.autofocus,
          onHighlightChanged: _handleHighlightChanged,
          splashColor: widget.splashColor,
          highlightColor: widget.highlightColor,
          focusColor: widget.focusColor,
          hoverColor: widget.hoverColor,
          onHover: _handleHoveredChanged,
          onTap: widget.onPressed,
          customBorder: effectiveShape,
          child: IconTheme.merge(
            data: IconThemeData(color: effectiveTextColor),
            child: Container(
              padding: widget.padding,
              child: Center(
                widthFactor: 1.0,
                heightFactor: 1.0,
                child: widget.child,
              ),
            ),
          ),
        ),
      ),
    );
    Size minSize;
    switch (widget.materialTapTargetSize) {
      case MaterialTapTargetSize.padded:
        minSize = const Size(48.0, 48.0);
        break;
      case MaterialTapTargetSize.shrinkWrap:
        minSize = Size.zero;
        break;
    }

    return Semantics(
      container: true,
      button: true,
      enabled: widget.enabled,
      child: _InputPadding(
        minSize: minSize,
        child: result,
      ),
    );
  }
}

/// A widget to pad the area around a [MaterialButton]'s inner [Material].
///
/// Redirect taps that occur in the padded area around the child to the center
/// of the child. This increases the size of the button and the button's
/// "tap target", but not its material or its ink splashes.
class _InputPadding extends SingleChildRenderObjectWidget {
  const _InputPadding({
    Key key,
    Widget child,
    this.minSize,
  }) : super(key: key, child: child);

  final Size minSize;

  @override
  RenderObject createRenderObject(BuildContext context) {
    return _RenderInputPadding(minSize);
  }

  @override
  void updateRenderObject(BuildContext context, covariant _RenderInputPadding renderObject) {
    renderObject.minSize = minSize;
  }
}

class _RenderInputPadding extends RenderShiftedBox {
  _RenderInputPadding(this._minSize, [RenderBox child]) : super(child);

  Size get minSize => _minSize;
  Size _minSize;
  set minSize(Size value) {
    if (_minSize == value)
      return;
    _minSize = value;
    markNeedsLayout();
  }

  @override
  double computeMinIntrinsicWidth(double height) {
    if (child != null)
      return math.max(child.getMinIntrinsicWidth(height), minSize.width);
    return 0.0;
  }

  @override
  double computeMinIntrinsicHeight(double width) {
    if (child != null)
      return math.max(child.getMinIntrinsicHeight(width), minSize.height);
    return 0.0;
  }

  @override
  double computeMaxIntrinsicWidth(double height) {
    if (child != null)
      return math.max(child.getMaxIntrinsicWidth(height), minSize.width);
    return 0.0;
  }

  @override
  double computeMaxIntrinsicHeight(double width) {
    if (child != null)
      return math.max(child.getMaxIntrinsicHeight(width), minSize.height);
    return 0.0;
  }

  @override
  void performLayout() {
    if (child != null) {
      child.layout(constraints, parentUsesSize: true);
      final double height = math.max(child.size.width, minSize.width);
      final double width = math.max(child.size.height, minSize.height);
      size = constraints.constrain(Size(height, width));
      final BoxParentData childParentData = child.parentData;
      childParentData.offset = Alignment.center.alongOffset(size - child.size);
    } else {
      size = Size.zero;
    }
  }

  @override
  bool hitTest(BoxHitTestResult result, { Offset position }) {
    if (super.hitTest(result, position: position)) {
      return true;
    }
    final Offset center = child.size.center(Offset.zero);
    return result.addWithRawTransform(
      transform: MatrixUtils.forceToPoint(center),
      position: center,
      hitTest: (BoxHitTestResult result, Offset position) {
        assert(position == center);
        return child.hitTest(result, position: center);
      },
    );
  }
}