packages/flutter/lib/src/material/bottom_sheet.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:async';

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

import 'colors.dart';
import 'material.dart';
import 'theme.dart';

const Duration _kBottomSheetDuration = const Duration(milliseconds: 200);
const double _kMinFlingVelocity = 700.0;
const double _kCloseProgressThreshold = 0.5;
const Color _kTransparent = const Color(0x00000000);
const Color _kBarrierColor = Colors.black54;

/// A material design bottom sheet.
///
/// There are two kinds of bottom sheets in material design:
///
///  * _Persistent_. A persistent bottom sheet shows information that
///    supplements the primary content of the app. A persistent bottom sheet
///    remains visible even when the user interacts with other parts of the app.
///    Persistent bottom sheets can be created and displayed with the
///    [ScaffoldState.showBottomSheet] function.
///
///  * _Modal_. A modal bottom sheet is an alternative to a menu or a dialog and
///    prevents the user from interacting with the rest of the app. Modal bottom
///    sheets can be created and displayed with the [showModalBottomSheet]
///    function.
///
/// The [BottomSheet] widget itself is rarely used directly. Instead, prefer to
/// create a persistent bottom sheet with [ScaffoldState.showBottomSheet] and a modal
/// bottom sheet with [showModalBottomSheet].
///
/// See also:
///
///  * [ScaffoldState.showBottomSheet]
///  * [showModalBottomSheet]
///  * <https://material.google.com/components/bottom-sheets.html>
class BottomSheet extends StatefulWidget {
  /// Creates a bottom sheet.
  ///
  /// Typically, bottom sheets are created implicitly by
  /// [ScaffoldState.showBottomSheet], for persistent bottom sheets, or by
  /// [showModalBottomSheet], for modal bottom sheets.
  const BottomSheet({
    Key key,
    this.animationController,
    @required this.onClosing,
    @required this.builder
  }) : assert(onClosing != null),
       assert(builder != null),
       super(key: key);

  /// The animation that controls the bottom sheet's position.
  ///
  /// The BottomSheet widget will manipulate the position of this animation, it
  /// is not just a passive observer.
  final AnimationController animationController;

  /// Called when the bottom sheet begins to close.
  ///
  /// A bottom sheet might be be prevented from closing (e.g., by user
  /// interaction) even after this callback is called. For this reason, this
  /// callback might be call multiple times for a given bottom sheet.
  final VoidCallback onClosing;

  /// A builder for the contents of the sheet.
  ///
  /// The bottom sheet will wrap the widget produced by this builder in a
  /// [Material] widget.
  final WidgetBuilder builder;

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

  /// Creates an animation controller suitable for controlling a [BottomSheet].
  static AnimationController createAnimationController(TickerProvider vsync) {
    return new AnimationController(
      duration: _kBottomSheetDuration,
      debugLabel: 'BottomSheet',
      vsync: vsync,
    );
  }
}

class _BottomSheetState extends State<BottomSheet> {

  final GlobalKey _childKey = new GlobalKey(debugLabel: 'BottomSheet child');

  double get _childHeight {
    final RenderBox renderBox = _childKey.currentContext.findRenderObject();
    return renderBox.size.height;
  }

  bool get _dismissUnderway => widget.animationController.status == AnimationStatus.reverse;

  void _handleDragUpdate(DragUpdateDetails details) {
    if (_dismissUnderway)
      return;
    widget.animationController.value -= details.primaryDelta / (_childHeight ?? details.primaryDelta);
  }

  void _handleDragEnd(DragEndDetails details) {
    if (_dismissUnderway)
      return;
    if (details.velocity.pixelsPerSecond.dy > _kMinFlingVelocity) {
      final double flingVelocity = -details.velocity.pixelsPerSecond.dy / _childHeight;
      if (widget.animationController.value > 0.0)
        widget.animationController.fling(velocity: flingVelocity);
      if (flingVelocity < 0.0)
        widget.onClosing();
    } else if (widget.animationController.value < _kCloseProgressThreshold) {
      if (widget.animationController.value > 0.0)
        widget.animationController.fling(velocity: -1.0);
      widget.onClosing();
    } else {
      widget.animationController.forward();
    }
  }

  @override
  Widget build(BuildContext context) {
    return new GestureDetector(
      onVerticalDragUpdate: _handleDragUpdate,
      onVerticalDragEnd: _handleDragEnd,
      child: new Material(
        key: _childKey,
        child: widget.builder(context)
      )
    );
  }
}

// PERSISTENT BOTTOM SHEETS

// See scaffold.dart


// MODAL BOTTOM SHEETS

class _ModalBottomSheetLayout extends SingleChildLayoutDelegate {
  _ModalBottomSheetLayout(this.progress);

  final double progress;

  @override
  BoxConstraints getConstraintsForChild(BoxConstraints constraints) {
    return new BoxConstraints(
      minWidth: constraints.maxWidth,
      maxWidth: constraints.maxWidth,
      minHeight: 0.0,
      maxHeight: constraints.maxHeight * 9.0 / 16.0
    );
  }

  @override
  Offset getPositionForChild(Size size, Size childSize) {
    return new Offset(0.0, size.height - childSize.height * progress);
  }

  @override
  bool shouldRelayout(_ModalBottomSheetLayout oldDelegate) {
    return progress != oldDelegate.progress;
  }
}

class _ModalBottomSheet<T> extends StatefulWidget {
  const _ModalBottomSheet({ Key key, this.route }) : super(key: key);

  final _ModalBottomSheetRoute<T> route;

  @override
  _ModalBottomSheetState<T> createState() => new _ModalBottomSheetState<T>();
}

class _ModalBottomSheetState<T> extends State<_ModalBottomSheet<T>> {
  @override
  Widget build(BuildContext context) {
    return new GestureDetector(
      onTap: () => Navigator.pop(context),
      child: new AnimatedBuilder(
        animation: widget.route.animation,
        builder: (BuildContext context, Widget child) {
          return new ClipRect(
            child: new CustomSingleChildLayout(
              delegate: new _ModalBottomSheetLayout(widget.route.animation.value),
              child: new BottomSheet(
                animationController: widget.route._animationController,
                onClosing: () => Navigator.pop(context),
                builder: widget.route.builder
              )
            )
          );
        }
      )
    );
  }
}

class _ModalBottomSheetRoute<T> extends PopupRoute<T> {
  _ModalBottomSheetRoute({
    this.builder,
    this.theme,
  });

  final WidgetBuilder builder;
  final ThemeData theme;

  @override
  Duration get transitionDuration => _kBottomSheetDuration;

  @override
  bool get barrierDismissible => true;

  @override
  Color get barrierColor => Colors.black54;

  AnimationController _animationController;

  @override
  AnimationController createAnimationController() {
    assert(_animationController == null);
    _animationController = BottomSheet.createAnimationController(navigator.overlay);
    return _animationController;
  }

  @override
  Widget buildPage(BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation) {
    Widget bottomSheet = new _ModalBottomSheet<T>(route: this);
    if (theme != null)
      bottomSheet = new Theme(data: theme, child: bottomSheet);
    return bottomSheet;
  }
}

/// Shows a modal material design bottom sheet.
///
/// A modal bottom sheet is an alternative to a menu or a dialog and prevents
/// the user from interacting with the rest of the app.
///
/// A closely related widget is a persistent bottom sheet, which shows
/// information that supplements the primary content of the app without
/// preventing the use from interacting with the app. Persistent bottom sheets
/// can be created and displayed with the [ScaffoldState.showBottomSheet] function.
///
/// Returns a `Future` that resolves to the value (if any) that was passed to
/// [Navigator.pop] when the modal bottom sheet was closed.
///
/// See also:
///
///  * [BottomSheet], which is the widget normally returned by the function
///    passed as the `builder` argument to [showModalBottomSheet].
///  * [ScaffoldState.showBottomSheet], for showing non-modal bottom sheets.
///  * <https://material.google.com/components/bottom-sheets.html#bottom-sheets-modal-bottom-sheets>
Future<T> showModalBottomSheet<T>({
  @required BuildContext context,
  @required WidgetBuilder builder,
}) {
  assert(context != null);
  assert(builder != null);
  return Navigator.push(context, new _ModalBottomSheetRoute<T>(
    builder: builder,
    theme: Theme.of(context, shadowThemeOnly: true),
  ));
}