packages/flutter/lib/src/widgets/gesture_detector.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/gestures.dart';
import 'package:flutter/rendering.dart';

import 'basic.dart';
import 'framework.dart';

export 'package:flutter/gestures.dart' show
  DragDownDetails,
  DragStartDetails,
  DragUpdateDetails,
  DragEndDetails,
  GestureTapDownCallback,
  GestureTapUpCallback,
  GestureTapCallback,
  GestureTapCancelCallback,
  GestureLongPressCallback,
  GestureLongPressStartCallback,
  GestureLongPressMoveUpdateCallback,
  GestureLongPressUpCallback,
  GestureLongPressEndCallback,
  GestureDragDownCallback,
  GestureDragStartCallback,
  GestureDragUpdateCallback,
  GestureDragEndCallback,
  GestureDragCancelCallback,
  GestureScaleStartCallback,
  GestureScaleUpdateCallback,
  GestureScaleEndCallback,
  GestureForcePressStartCallback,
  GestureForcePressPeakCallback,
  GestureForcePressEndCallback,
  GestureForcePressUpdateCallback,
  LongPressStartDetails,
  LongPressMoveUpdateDetails,
  LongPressEndDetails,
  ScaleStartDetails,
  ScaleUpdateDetails,
  ScaleEndDetails,
  TapDownDetails,
  TapUpDetails,
  ForcePressDetails,
  Velocity;

// Examples can assume:
// bool _lights;
// void setState(VoidCallback fn) { }
// String _last;

/// Factory for creating gesture recognizers.
///
/// `T` is the type of gesture recognizer this class manages.
///
/// Used by [RawGestureDetector.gestures].
@optionalTypeArgs
abstract class GestureRecognizerFactory<T extends GestureRecognizer> {
  /// Abstract const constructor. This constructor enables subclasses to provide
  /// const constructors so that they can be used in const expressions.
  const GestureRecognizerFactory();

  /// Must return an instance of T.
  T constructor();

  /// Must configure the given instance (which will have been created by
  /// `constructor`).
  ///
  /// This normally means setting the callbacks.
  void initializer(T instance);

  bool _debugAssertTypeMatches(Type type) {
    assert(type == T, 'GestureRecognizerFactory of type $T was used where type $type was specified.');
    return true;
  }
}

/// Signature for closures that implement [GestureRecognizerFactory.constructor].
typedef GestureRecognizerFactoryConstructor<T extends GestureRecognizer> = T Function();

/// Signature for closures that implement [GestureRecognizerFactory.initializer].
typedef GestureRecognizerFactoryInitializer<T extends GestureRecognizer> = void Function(T instance);

/// Factory for creating gesture recognizers that delegates to callbacks.
///
/// Used by [RawGestureDetector.gestures].
class GestureRecognizerFactoryWithHandlers<T extends GestureRecognizer> extends GestureRecognizerFactory<T> {
  /// Creates a gesture recognizer factory with the given callbacks.
  ///
  /// The arguments must not be null.
  const GestureRecognizerFactoryWithHandlers(this._constructor, this._initializer)
    : assert(_constructor != null),
      assert(_initializer != null);

  final GestureRecognizerFactoryConstructor<T> _constructor;

  final GestureRecognizerFactoryInitializer<T> _initializer;

  @override
  T constructor() => _constructor();

  @override
  void initializer(T instance) => _initializer(instance);
}

/// A widget that detects gestures.
///
/// Attempts to recognize gestures that correspond to its non-null callbacks.
///
/// If this widget has a child, it defers to that child for its sizing behavior.
/// If it does not have a child, it grows to fit the parent instead.
///
/// By default a GestureDetector with an invisible child ignores touches;
/// this behavior can be controlled with [behavior].
///
/// GestureDetector also listens for accessibility events and maps
/// them to the callbacks. To ignore accessibility events, set
/// [excludeFromSemantics] to true.
///
/// See <http://flutter.dev/gestures/> for additional information.
///
/// Material design applications typically react to touches with ink splash
/// effects. The [InkWell] class implements this effect and can be used in place
/// of a [GestureDetector] for handling taps.
///
/// {@tool sample}
///
/// This example makes a rectangle react to being tapped by setting the
/// `_lights` field:
///
/// ```dart
/// GestureDetector(
///   onTap: () {
///     setState(() { _lights = true; });
///   },
///   child: Container(
///     color: Colors.yellow,
///     child: Text('TURN LIGHTS ON'),
///   ),
/// )
/// ```
/// {@end-tool}
///
/// ## Debugging
///
/// To see how large the hit test box of a [GestureDetector] is for debugging
/// purposes, set [debugPaintPointersEnabled] to true.
class GestureDetector extends StatelessWidget {
  /// Creates a widget that detects gestures.
  ///
  /// Pan and scale callbacks cannot be used simultaneously because scale is a
  /// superset of pan. Simply use the scale callbacks instead.
  ///
  /// Horizontal and vertical drag callbacks cannot be used simultaneously
  /// because a combination of a horizontal and vertical drag is a pan. Simply
  /// use the pan callbacks instead.
  ///
  /// By default, gesture detectors contribute semantic information to the tree
  /// that is used by assistive technology.
  GestureDetector({
    Key key,
    this.child,
    this.onTapDown,
    this.onTapUp,
    this.onTap,
    this.onTapCancel,
    this.onDoubleTap,
    this.onLongPress,
    this.onLongPressStart,
    this.onLongPressMoveUpdate,
    this.onLongPressUp,
    this.onLongPressEnd,
    this.onVerticalDragDown,
    this.onVerticalDragStart,
    this.onVerticalDragUpdate,
    this.onVerticalDragEnd,
    this.onVerticalDragCancel,
    this.onHorizontalDragDown,
    this.onHorizontalDragStart,
    this.onHorizontalDragUpdate,
    this.onHorizontalDragEnd,
    this.onHorizontalDragCancel,
    this.onForcePressStart,
    this.onForcePressPeak,
    this.onForcePressUpdate,
    this.onForcePressEnd,
    this.onPanDown,
    this.onPanStart,
    this.onPanUpdate,
    this.onPanEnd,
    this.onPanCancel,
    this.onScaleStart,
    this.onScaleUpdate,
    this.onScaleEnd,
    this.behavior,
    this.excludeFromSemantics = false,
    this.dragStartBehavior = DragStartBehavior.start,
  }) : assert(excludeFromSemantics != null),
       assert(dragStartBehavior != null),
       assert(() {
         final bool haveVerticalDrag = onVerticalDragStart != null || onVerticalDragUpdate != null || onVerticalDragEnd != null;
         final bool haveHorizontalDrag = onHorizontalDragStart != null || onHorizontalDragUpdate != null || onHorizontalDragEnd != null;
         final bool havePan = onPanStart != null || onPanUpdate != null || onPanEnd != null;
         final bool haveScale = onScaleStart != null || onScaleUpdate != null || onScaleEnd != null;
         if (havePan || haveScale) {
           if (havePan && haveScale) {
             throw FlutterError(
               'Incorrect GestureDetector arguments.\n'
               'Having both a pan gesture recognizer and a scale gesture recognizer is redundant; scale is a superset of pan. Just use the scale gesture recognizer.'
             );
           }
           final String recognizer = havePan ? 'pan' : 'scale';
           if (haveVerticalDrag && haveHorizontalDrag) {
             throw FlutterError(
               'Incorrect GestureDetector arguments.\n'
               'Simultaneously having a vertical drag gesture recognizer, a horizontal drag gesture recognizer, and a $recognizer gesture recognizer '
               'will result in the $recognizer gesture recognizer being ignored, since the other two will catch all drags.'
             );
           }
         }
         return true;
       }()),
       super(key: key);

  /// The widget below this widget in the tree.
  ///
  /// {@macro flutter.widgets.child}
  final Widget child;

  /// A pointer that might cause a tap has contacted the screen at a particular
  /// location.
  ///
  /// This is called after a short timeout, even if the winning gesture has not
  /// yet been selected. If the tap gesture wins, [onTapUp] will be called,
  /// otherwise [onTapCancel] will be called.
  final GestureTapDownCallback onTapDown;

  /// A pointer that will trigger a tap has stopped contacting the screen at a
  /// particular location.
  ///
  /// This triggers immediately before [onTap] in the case of the tap gesture
  /// winning. If the tap gesture did not win, [onTapCancel] is called instead.
  final GestureTapUpCallback onTapUp;

  /// A tap has occurred.
  ///
  /// This triggers when the tap gesture wins. If the tap gesture did not win,
  /// [onTapCancel] is called instead.
  ///
  /// See also:
  ///
  ///  * [onTapUp], which is called at the same time but includes details
  ///    regarding the pointer position.
  final GestureTapCallback onTap;

  /// The pointer that previously triggered [onTapDown] will not end up causing
  /// a tap.
  ///
  /// This is called after [onTapDown], and instead of [onTapUp] and [onTap], if
  /// the tap gesture did not win.
  final GestureTapCancelCallback onTapCancel;

  /// The user has tapped the screen at the same location twice in quick
  /// succession.
  final GestureTapCallback onDoubleTap;

  /// Called when a long press gesture has been recognized.
  ///
  /// Triggered when a pointer has remained in contact with the screen at the
  /// same location for a long period of time.
  ///
  /// See also:
  ///
  ///  * [onLongPressStart], which has the same timing but has data for the
  ///    press location.
  final GestureLongPressCallback onLongPress;

  /// Callback for long press start with gesture location.
  ///
  /// Triggered when a pointer has remained in contact with the screen at the
  /// same location for a long period of time.
  ///
  /// See also:
  ///
  ///  * [onLongPress], which has the same timing but without the location data.
  final GestureLongPressStartCallback onLongPressStart;

  /// A pointer has been drag-moved after a long press.
  final GestureLongPressMoveUpdateCallback onLongPressMoveUpdate;

  /// A pointer that has triggered a long-press has stopped contacting the screen.
  ///
  /// See also:
  ///
  ///  * [onLongPressEnd], which has the same timing but has data for the up
  ///    gesture location.
  final GestureLongPressUpCallback onLongPressUp;

  /// A pointer that has triggered a long-press has stopped contacting the screen.
  ///
  /// See also:
  ///
  ///  * [onLongPressUp], which has the same timing but without the location data.
  final GestureLongPressEndCallback onLongPressEnd;

  /// A pointer has contacted the screen and might begin to move vertically.
  final GestureDragDownCallback onVerticalDragDown;

  /// A pointer has contacted the screen and has begun to move vertically.
  final GestureDragStartCallback onVerticalDragStart;

  /// A pointer that is in contact with the screen and moving vertically has
  /// moved in the vertical direction.
  final GestureDragUpdateCallback onVerticalDragUpdate;

  /// A pointer that was previously in contact with the screen and moving
  /// vertically is no longer in contact with the screen and was moving at a
  /// specific velocity when it stopped contacting the screen.
  final GestureDragEndCallback onVerticalDragEnd;

  /// The pointer that previously triggered [onVerticalDragDown] did not
  /// complete.
  final GestureDragCancelCallback onVerticalDragCancel;

  /// A pointer has contacted the screen and might begin to move horizontally.
  final GestureDragDownCallback onHorizontalDragDown;

  /// A pointer has contacted the screen and has begun to move horizontally.
  final GestureDragStartCallback onHorizontalDragStart;

  /// A pointer that is in contact with the screen and moving horizontally has
  /// moved in the horizontal direction.
  final GestureDragUpdateCallback onHorizontalDragUpdate;

  /// A pointer that was previously in contact with the screen and moving
  /// horizontally is no longer in contact with the screen and was moving at a
  /// specific velocity when it stopped contacting the screen.
  final GestureDragEndCallback onHorizontalDragEnd;

  /// The pointer that previously triggered [onHorizontalDragDown] did not
  /// complete.
  final GestureDragCancelCallback onHorizontalDragCancel;

  /// A pointer has contacted the screen and might begin to move.
  final GestureDragDownCallback onPanDown;

  /// A pointer has contacted the screen and has begun to move.
  final GestureDragStartCallback onPanStart;

  /// A pointer that is in contact with the screen and moving has moved again.
  final GestureDragUpdateCallback onPanUpdate;

  /// A pointer that was previously in contact with the screen and moving
  /// is no longer in contact with the screen and was moving at a specific
  /// velocity when it stopped contacting the screen.
  final GestureDragEndCallback onPanEnd;

  /// The pointer that previously triggered [onPanDown] did not complete.
  final GestureDragCancelCallback onPanCancel;

  /// The pointers in contact with the screen have established a focal point and
  /// initial scale of 1.0.
  final GestureScaleStartCallback onScaleStart;

  /// The pointers in contact with the screen have indicated a new focal point
  /// and/or scale.
  final GestureScaleUpdateCallback onScaleUpdate;

  /// The pointers are no longer in contact with the screen.
  final GestureScaleEndCallback onScaleEnd;

  /// The pointer is in contact with the screen and has pressed with sufficient
  /// force to initiate a force press. The amount of force is at least
  /// [ForcePressGestureRecognizer.startPressure].
  ///
  /// Note that this callback will only be fired on devices with pressure
  /// detecting screens.
  final GestureForcePressStartCallback onForcePressStart;

  /// The pointer is in contact with the screen and has pressed with the maximum
  /// force. The amount of force is at least
  /// [ForcePressGestureRecognizer.peakPressure].
  ///
  /// Note that this callback will only be fired on devices with pressure
  /// detecting screens.
  final GestureForcePressPeakCallback onForcePressPeak;

  /// A pointer is in contact with the screen, has previously passed the
  /// [ForcePressGestureRecognizer.startPressure] and is either moving on the
  /// plane of the screen, pressing the screen with varying forces or both
  /// simultaneously.
  ///
  /// Note that this callback will only be fired on devices with pressure
  /// detecting screens.
  final GestureForcePressUpdateCallback onForcePressUpdate;

  /// The pointer is no longer in contact with the screen.
  ///
  /// Note that this callback will only be fired on devices with pressure
  /// detecting screens.
  final GestureForcePressEndCallback onForcePressEnd;

  /// How this gesture detector should behave during hit testing.
  ///
  /// This defaults to [HitTestBehavior.deferToChild] if [child] is not null and
  /// [HitTestBehavior.translucent] if child is null.
  final HitTestBehavior behavior;

  /// Whether to exclude these gestures from the semantics tree. For
  /// example, the long-press gesture for showing a tooltip is
  /// excluded because the tooltip itself is included in the semantics
  /// tree directly and so having a gesture to show it would result in
  /// duplication of information.
  final bool excludeFromSemantics;

  /// Determines the way that drag start behavior is handled.
  ///
  /// If set to [DragStartBehavior.start], gesture drag behavior will
  /// begin upon the detection of a drag gesture. If set to
  /// [DragStartBehavior.down] it will begin when a down event is first detected.
  ///
  /// In general, setting this to [DragStartBehavior.start] will make drag
  /// animation smoother and setting it to [DragStartBehavior.down] will make
  /// drag behavior feel slightly more reactive.
  ///
  /// By default, the drag start behavior is [DragStartBehavior.start].
  ///
  /// Only the [onStart] callbacks for the [VerticalDragGestureRecognizer],
  /// [HorizontalDragGestureRecognizer] and [PanGestureRecognizer] are affected
  /// by this setting.
  ///
  /// See also:
  ///
  ///  * [DragGestureRecognizer.dragStartBehavior], which gives an example for the different behaviors.
  final DragStartBehavior dragStartBehavior;

  @override
  Widget build(BuildContext context) {
    final Map<Type, GestureRecognizerFactory> gestures = <Type, GestureRecognizerFactory>{};

    if (onTapDown != null || onTapUp != null || onTap != null || onTapCancel != null) {
      gestures[TapGestureRecognizer] = GestureRecognizerFactoryWithHandlers<TapGestureRecognizer>(
        () => TapGestureRecognizer(debugOwner: this),
        (TapGestureRecognizer instance) {
          instance
            ..onTapDown = onTapDown
            ..onTapUp = onTapUp
            ..onTap = onTap
            ..onTapCancel = onTapCancel;
        },
      );
    }

    if (onDoubleTap != null) {
      gestures[DoubleTapGestureRecognizer] = GestureRecognizerFactoryWithHandlers<DoubleTapGestureRecognizer>(
        () => DoubleTapGestureRecognizer(debugOwner: this),
        (DoubleTapGestureRecognizer instance) {
          instance
            ..onDoubleTap = onDoubleTap;
        },
      );
    }

    if (onLongPress != null ||
        onLongPressUp != null ||
        onLongPressStart != null ||
        onLongPressMoveUpdate != null ||
        onLongPressEnd != null) {
      gestures[LongPressGestureRecognizer] = GestureRecognizerFactoryWithHandlers<LongPressGestureRecognizer>(
        () => LongPressGestureRecognizer(debugOwner: this),
        (LongPressGestureRecognizer instance) {
          instance
            ..onLongPress = onLongPress
            ..onLongPressStart = onLongPressStart
            ..onLongPressMoveUpdate = onLongPressMoveUpdate
            ..onLongPressEnd =onLongPressEnd
            ..onLongPressUp = onLongPressUp;
        },
      );
    }

    if (onVerticalDragDown != null ||
        onVerticalDragStart != null ||
        onVerticalDragUpdate != null ||
        onVerticalDragEnd != null ||
        onVerticalDragCancel != null) {
      gestures[VerticalDragGestureRecognizer] = GestureRecognizerFactoryWithHandlers<VerticalDragGestureRecognizer>(
        () => VerticalDragGestureRecognizer(debugOwner: this),
        (VerticalDragGestureRecognizer instance) {
          instance
            ..onDown = onVerticalDragDown
            ..onStart = onVerticalDragStart
            ..onUpdate = onVerticalDragUpdate
            ..onEnd = onVerticalDragEnd
            ..onCancel = onVerticalDragCancel
            ..dragStartBehavior = dragStartBehavior;
        },
      );
    }

    if (onHorizontalDragDown != null ||
        onHorizontalDragStart != null ||
        onHorizontalDragUpdate != null ||
        onHorizontalDragEnd != null ||
        onHorizontalDragCancel != null) {
      gestures[HorizontalDragGestureRecognizer] = GestureRecognizerFactoryWithHandlers<HorizontalDragGestureRecognizer>(
        () => HorizontalDragGestureRecognizer(debugOwner: this),
        (HorizontalDragGestureRecognizer instance) {
          instance
            ..onDown = onHorizontalDragDown
            ..onStart = onHorizontalDragStart
            ..onUpdate = onHorizontalDragUpdate
            ..onEnd = onHorizontalDragEnd
            ..onCancel = onHorizontalDragCancel
            ..dragStartBehavior = dragStartBehavior;
        },
      );
    }

    if (onPanDown != null ||
        onPanStart != null ||
        onPanUpdate != null ||
        onPanEnd != null ||
        onPanCancel != null) {
      gestures[PanGestureRecognizer] = GestureRecognizerFactoryWithHandlers<PanGestureRecognizer>(
        () => PanGestureRecognizer(debugOwner: this),
        (PanGestureRecognizer instance) {
          instance
            ..onDown = onPanDown
            ..onStart = onPanStart
            ..onUpdate = onPanUpdate
            ..onEnd = onPanEnd
            ..onCancel = onPanCancel
            ..dragStartBehavior = dragStartBehavior;
        },
      );
    }

    if (onScaleStart != null || onScaleUpdate != null || onScaleEnd != null) {
      gestures[ScaleGestureRecognizer] = GestureRecognizerFactoryWithHandlers<ScaleGestureRecognizer>(
        () => ScaleGestureRecognizer(debugOwner: this),
        (ScaleGestureRecognizer instance) {
          instance
            ..onStart = onScaleStart
            ..onUpdate = onScaleUpdate
            ..onEnd = onScaleEnd;
        },
      );
    }

    if (onForcePressStart != null ||
        onForcePressPeak != null ||
        onForcePressUpdate != null ||
        onForcePressEnd != null) {
      gestures[ForcePressGestureRecognizer] = GestureRecognizerFactoryWithHandlers<ForcePressGestureRecognizer>(
        () => ForcePressGestureRecognizer(debugOwner: this),
        (ForcePressGestureRecognizer instance) {
          instance
            ..onStart = onForcePressStart
            ..onPeak = onForcePressPeak
            ..onUpdate = onForcePressUpdate
            ..onEnd = onForcePressEnd;
        },
      );
    }

    return RawGestureDetector(
      gestures: gestures,
      behavior: behavior,
      excludeFromSemantics: excludeFromSemantics,
      child: child,
    );
  }
  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(EnumProperty<DragStartBehavior>('startBehavior', dragStartBehavior));
  }
}

/// A widget that detects gestures described by the given gesture
/// factories.
///
/// For common gestures, use a [GestureRecognizer].
/// [RawGestureDetector] is useful primarily when developing your
/// own gesture recognizers.
///
/// Configuring the gesture recognizers requires a carefully constructed map, as
/// described in [gestures] and as shown in the example below.
///
/// {@tool sample}
///
/// This example shows how to hook up a [TapGestureRecognizer]. It assumes that
/// the code is being used inside a [State] object with a `_last` field that is
/// then displayed as the child of the gesture detector.
///
/// ```dart
/// RawGestureDetector(
///   gestures: <Type, GestureRecognizerFactory>{
///     TapGestureRecognizer: GestureRecognizerFactoryWithHandlers<TapGestureRecognizer>(
///       () => TapGestureRecognizer(),
///       (TapGestureRecognizer instance) {
///         instance
///           ..onTapDown = (TapDownDetails details) { setState(() { _last = 'down'; }); }
///           ..onTapUp = (TapUpDetails details) { setState(() { _last = 'up'; }); }
///           ..onTap = () { setState(() { _last = 'tap'; }); }
///           ..onTapCancel = () { setState(() { _last = 'cancel'; }); };
///       },
///     ),
///   },
///   child: Container(width: 300.0, height: 300.0, color: Colors.yellow, child: Text(_last)),
/// )
/// ```
/// {@end-tool}
///
/// See also:
///
///  * [GestureDetector], a less flexible but much simpler widget that does the same thing.
///  * [Listener], a widget that reports raw pointer events.
///  * [GestureRecognizer], the class that you extend to create a custom gesture recognizer.
class RawGestureDetector extends StatefulWidget {
  /// Creates a widget that detects gestures.
  ///
  /// By default, gesture detectors contribute semantic information to the tree
  /// that is used by assistive technology. This can be controlled using
  /// [excludeFromSemantics].
  const RawGestureDetector({
    Key key,
    this.child,
    this.gestures = const <Type, GestureRecognizerFactory>{},
    this.behavior,
    this.excludeFromSemantics = false,
  }) : assert(gestures != null),
       assert(excludeFromSemantics != null),
       super(key: key);

  /// The widget below this widget in the tree.
  ///
  /// {@macro flutter.widgets.child}
  final Widget child;

  /// The gestures that this widget will attempt to recognize.
  ///
  /// This should be a map from [GestureRecognizer] subclasses to
  /// [GestureRecognizerFactory] subclasses specialized with the same type.
  ///
  /// This value can be late-bound at layout time using
  /// [RawGestureDetectorState.replaceGestureRecognizers].
  final Map<Type, GestureRecognizerFactory> gestures;

  /// How this gesture detector should behave during hit testing.
  ///
  /// This defaults to [HitTestBehavior.deferToChild] if [child] is not null and
  /// [HitTestBehavior.translucent] if child is null.
  final HitTestBehavior behavior;

  /// Whether to exclude these gestures from the semantics tree. For
  /// example, the long-press gesture for showing a tooltip is
  /// excluded because the tooltip itself is included in the semantics
  /// tree directly and so having a gesture to show it would result in
  /// duplication of information.
  final bool excludeFromSemantics;

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

/// State for a [RawGestureDetector].
class RawGestureDetectorState extends State<RawGestureDetector> {
  Map<Type, GestureRecognizer> _recognizers = const <Type, GestureRecognizer>{};

  @override
  void initState() {
    super.initState();
    _syncAll(widget.gestures);
  }

  @override
  void didUpdateWidget(RawGestureDetector oldWidget) {
    super.didUpdateWidget(oldWidget);
    _syncAll(widget.gestures);
  }

  /// This method can be called after the build phase, during the
  /// layout of the nearest descendant [RenderObjectWidget] of the
  /// gesture detector, to update the list of active gesture
  /// recognizers.
  ///
  /// The typical use case is [Scrollable]s, which put their viewport
  /// in their gesture detector, and then need to know the dimensions
  /// of the viewport and the viewport's child to determine whether
  /// the gesture detector should be enabled.
  ///
  /// The argument should follow the same conventions as
  /// [RawGestureDetector.gestures]. It acts like a temporary replacement for
  /// that value until the next build.
  void replaceGestureRecognizers(Map<Type, GestureRecognizerFactory> gestures) {
    assert(() {
      if (!context.findRenderObject().owner.debugDoingLayout) {
        throw FlutterError(
          'Unexpected call to replaceGestureRecognizers() method of RawGestureDetectorState.\n'
          'The replaceGestureRecognizers() method can only be called during the layout phase. '
          'To set the gesture recognizers at other times, trigger a new build using setState() '
          'and provide the new gesture recognizers as constructor arguments to the corresponding '
          'RawGestureDetector or GestureDetector object.'
        );
      }
      return true;
    }());
    _syncAll(gestures);
    if (!widget.excludeFromSemantics) {
      final RenderSemanticsGestureHandler semanticsGestureHandler = context.findRenderObject();
      context.visitChildElements((Element element) {
        final _GestureSemantics widget = element.widget;
        widget._updateHandlers(semanticsGestureHandler);
      });
    }
  }

  /// This method can be called outside of the build phase to filter the list of
  /// available semantic actions.
  ///
  /// The actual filtering is happening in the next frame and a frame will be
  /// scheduled if non is pending.
  ///
  /// This is used by [Scrollable] to configure system accessibility tools so
  /// that they know in which direction a particular list can be scrolled.
  ///
  /// If this is never called, then the actions are not filtered. If the list of
  /// actions to filter changes, it must be called again.
  void replaceSemanticsActions(Set<SemanticsAction> actions) {
    assert(() {
      final Element element = context;
      if (element.owner.debugBuilding) {
        throw FlutterError(
          'Unexpected call to replaceSemanticsActions() method of RawGestureDetectorState.\n'
          'The replaceSemanticsActions() method can only be called outside of the build phase.'
        );
      }
      return true;
    }());
    if (!widget.excludeFromSemantics) {
      final RenderSemanticsGestureHandler semanticsGestureHandler = context.findRenderObject();
      semanticsGestureHandler.validActions = actions; // will call _markNeedsSemanticsUpdate(), if required.
    }
  }

  @override
  void dispose() {
    for (GestureRecognizer recognizer in _recognizers.values)
      recognizer.dispose();
    _recognizers = null;
    super.dispose();
  }

  void _syncAll(Map<Type, GestureRecognizerFactory> gestures) {
    assert(_recognizers != null);
    final Map<Type, GestureRecognizer> oldRecognizers = _recognizers;
    _recognizers = <Type, GestureRecognizer>{};
    for (Type type in gestures.keys) {
      assert(gestures[type] != null);
      assert(gestures[type]._debugAssertTypeMatches(type));
      assert(!_recognizers.containsKey(type));
      _recognizers[type] = oldRecognizers[type] ?? gestures[type].constructor();
      assert(_recognizers[type].runtimeType == type, 'GestureRecognizerFactory of type $type created a GestureRecognizer of type ${_recognizers[type].runtimeType}. The GestureRecognizerFactory must be specialized with the type of the class that it returns from its constructor method.');
      gestures[type].initializer(_recognizers[type]);
    }
    for (Type type in oldRecognizers.keys) {
      if (!_recognizers.containsKey(type))
        oldRecognizers[type].dispose();
    }
  }

  void _handlePointerDown(PointerDownEvent event) {
    assert(_recognizers != null);
    for (GestureRecognizer recognizer in _recognizers.values)
      recognizer.addPointer(event);
  }

  HitTestBehavior get _defaultBehavior {
    return widget.child == null ? HitTestBehavior.translucent : HitTestBehavior.deferToChild;
  }

  void _handleSemanticsTap() {
    final TapGestureRecognizer recognizer = _recognizers[TapGestureRecognizer];
    assert(recognizer != null);
    if (recognizer.onTapDown != null)
      recognizer.onTapDown(TapDownDetails());
    if (recognizer.onTapUp != null)
      recognizer.onTapUp(TapUpDetails());
    if (recognizer.onTap != null)
      recognizer.onTap();
  }

  void _handleSemanticsLongPress() {
    final LongPressGestureRecognizer recognizer = _recognizers[LongPressGestureRecognizer];
    assert(recognizer != null);
    if (recognizer.onLongPress != null)
      recognizer.onLongPress();
  }

  void _handleSemanticsHorizontalDragUpdate(DragUpdateDetails updateDetails) {
    {
      final HorizontalDragGestureRecognizer recognizer = _recognizers[HorizontalDragGestureRecognizer];
      if (recognizer != null) {
        if (recognizer.onDown != null)
          recognizer.onDown(DragDownDetails());
        if (recognizer.onStart != null)
          recognizer.onStart(DragStartDetails());
        if (recognizer.onUpdate != null)
          recognizer.onUpdate(updateDetails);
        if (recognizer.onEnd != null)
          recognizer.onEnd(DragEndDetails(primaryVelocity: 0.0));
        return;
      }
    }
    {
      final PanGestureRecognizer recognizer = _recognizers[PanGestureRecognizer];
      if (recognizer != null) {
        if (recognizer.onDown != null)
          recognizer.onDown(DragDownDetails());
        if (recognizer.onStart != null)
          recognizer.onStart(DragStartDetails());
        if (recognizer.onUpdate != null)
          recognizer.onUpdate(updateDetails);
        if (recognizer.onEnd != null)
          recognizer.onEnd(DragEndDetails());
        return;
      }
    }
  }

  void _handleSemanticsVerticalDragUpdate(DragUpdateDetails updateDetails) {
    {
      final VerticalDragGestureRecognizer recognizer = _recognizers[VerticalDragGestureRecognizer];
      if (recognizer != null) {
        if (recognizer.onDown != null)
          recognizer.onDown(DragDownDetails());
        if (recognizer.onStart != null)
          recognizer.onStart(DragStartDetails());
        if (recognizer.onUpdate != null)
          recognizer.onUpdate(updateDetails);
        if (recognizer.onEnd != null)
          recognizer.onEnd(DragEndDetails(primaryVelocity: 0.0));
        return;
      }
    }
    {
      final PanGestureRecognizer recognizer = _recognizers[PanGestureRecognizer];
      if (recognizer != null) {
        if (recognizer.onDown != null)
          recognizer.onDown(DragDownDetails());
        if (recognizer.onStart != null)
          recognizer.onStart(DragStartDetails());
        if (recognizer.onUpdate != null)
          recognizer.onUpdate(updateDetails);
        if (recognizer.onEnd != null)
          recognizer.onEnd(DragEndDetails());
        return;
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    Widget result = Listener(
      onPointerDown: _handlePointerDown,
      behavior: widget.behavior ?? _defaultBehavior,
      child: widget.child,
    );
    if (!widget.excludeFromSemantics)
      result = _GestureSemantics(owner: this, child: result);
    return result;
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    if (_recognizers == null) {
      properties.add(DiagnosticsNode.message('DISPOSED'));
    } else {
      final List<String> gestures = _recognizers.values.map<String>((GestureRecognizer recognizer) => recognizer.debugDescription).toList();
      properties.add(IterableProperty<String>('gestures', gestures, ifEmpty: '<none>'));
      properties.add(IterableProperty<GestureRecognizer>('recognizers', _recognizers.values, level: DiagnosticLevel.fine));
    }
    properties.add(EnumProperty<HitTestBehavior>('behavior', widget.behavior, defaultValue: null));
  }
}

class _GestureSemantics extends SingleChildRenderObjectWidget {
  const _GestureSemantics({
    Key key,
    Widget child,
    this.owner,
  }) : super(key: key, child: child);

  final RawGestureDetectorState owner;

  @override
  RenderSemanticsGestureHandler createRenderObject(BuildContext context) {
    return RenderSemanticsGestureHandler(
      onTap: _onTapHandler,
      onLongPress: _onLongPressHandler,
      onHorizontalDragUpdate: _onHorizontalDragUpdateHandler,
      onVerticalDragUpdate: _onVerticalDragUpdateHandler,
    );
  }

  void _updateHandlers(RenderSemanticsGestureHandler renderObject) {
    renderObject
      ..onTap = _onTapHandler
      ..onLongPress = _onLongPressHandler
      ..onHorizontalDragUpdate = _onHorizontalDragUpdateHandler
      ..onVerticalDragUpdate = _onVerticalDragUpdateHandler;
  }

  @override
  void updateRenderObject(BuildContext context, RenderSemanticsGestureHandler renderObject) {
    _updateHandlers(renderObject);
  }

  GestureTapCallback get _onTapHandler {
    return owner._recognizers.containsKey(TapGestureRecognizer) ? owner._handleSemanticsTap : null;
  }

  GestureTapCallback get _onLongPressHandler {
    return owner._recognizers.containsKey(LongPressGestureRecognizer) ? owner._handleSemanticsLongPress : null;
  }

  GestureDragUpdateCallback get _onHorizontalDragUpdateHandler {
    return owner._recognizers.containsKey(HorizontalDragGestureRecognizer) ||
        owner._recognizers.containsKey(PanGestureRecognizer) ? owner._handleSemanticsHorizontalDragUpdate : null;
  }

  GestureDragUpdateCallback get _onVerticalDragUpdateHandler {
    return owner._recognizers.containsKey(VerticalDragGestureRecognizer) ||
        owner._recognizers.containsKey(PanGestureRecognizer) ? owner._handleSemanticsVerticalDragUpdate : null;
  }
}