• Greg Spencer's avatar
    Remove 'must not be null' comments from various libraries. (#134984) · 8cda3bea
    Greg Spencer authored
    ## Description
    
    This removes all of the comments that are of the form "so-and-so (must not be null|can ?not be null|must be non-null)" from the cases where those values are defines as non-nullable values.
    
    This PR removes them from the animation, cupertino, foundation, gestures, semantics, and services libraries.  Each of them only had a few, so I lumped them together.
    
    This was done by hand, since it really didn't lend itself to scripting, so it needs to be more than just spot-checked, I think. I was careful to leave any comment that referred to parameters that were nullable, but I may have missed some.
    
    In addition to being no longer relevant after null safety has been made the default, these comments were largely fragile, in that it was easy for them to get out of date, and not be accurate anymore anyhow.
    
    This did create a number of constructor comments which basically say "Creates a [Foo].", but I don't really know how to avoid that in a large scale change, since there's not much you can really say in a lot of cases.  I think we might consider some leniency for constructors to the "Comment must be meaningful" style guidance (which we de facto have already, since there are a bunch of these).
    
    ## Related PRs
    - https://github.com/flutter/flutter/pull/134991
    - https://github.com/flutter/flutter/pull/134992
    - https://github.com/flutter/flutter/pull/134993
    - https://github.com/flutter/flutter/pull/134994
    
    ## Tests
     - Documentation only change.
    Unverified
    8cda3bea
long_press.dart 31.7 KB
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// Copyright 2014 The Flutter 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 'constants.dart';
import 'events.dart';
import 'recognizer.dart';
import 'velocity_tracker.dart';

export 'dart:ui' show Offset, PointerDeviceKind;

export 'arena.dart' show GestureDisposition;
export 'events.dart' show PointerDownEvent, PointerEvent;
export 'velocity_tracker.dart' show Velocity;

/// Callback signature for [LongPressGestureRecognizer.onLongPressDown].
///
/// Called when a pointer that might cause a long-press has contacted the
/// screen. The position at which the pointer contacted the screen is available
/// in the `details`.
///
/// See also:
///
///  * [GestureDetector.onLongPressDown], which matches this signature.
///  * [GestureLongPressStartCallback], the signature that gets called when the
///    pointer has been in contact with the screen long enough to be considered
///    a long-press.
typedef GestureLongPressDownCallback = void Function(LongPressDownDetails details);

/// Callback signature for [LongPressGestureRecognizer.onLongPressCancel].
///
/// Called when the pointer that previously triggered a
/// [GestureLongPressDownCallback] will not end up causing a long-press.
///
/// See also:
///
///  * [GestureDetector.onLongPressCancel], which matches this signature.
typedef GestureLongPressCancelCallback = void Function();

/// Callback signature for [LongPressGestureRecognizer.onLongPress].
///
/// Called when a pointer has remained in contact with the screen at the
/// same location for a long period of time.
///
/// See also:
///
///  * [GestureDetector.onLongPress], which matches this signature.
///  * [GestureLongPressStartCallback], which is the same signature but with
///    details of where the long press occurred.
typedef GestureLongPressCallback = void Function();

/// Callback signature for [LongPressGestureRecognizer.onLongPressUp].
///
/// Called when a pointer stops contacting the screen after a long press
/// gesture was detected.
///
/// See also:
///
///  * [GestureDetector.onLongPressUp], which matches this signature.
typedef GestureLongPressUpCallback = void Function();

/// Callback signature for [LongPressGestureRecognizer.onLongPressStart].
///
/// Called when a pointer has remained in contact with the screen at the
/// same location for a long period of time. Also reports the long press down
/// position.
///
/// See also:
///
///  * [GestureDetector.onLongPressStart], which matches this signature.
///  * [GestureLongPressCallback], which is the same signature without the
///    details.
typedef GestureLongPressStartCallback = void Function(LongPressStartDetails details);

/// Callback signature for [LongPressGestureRecognizer.onLongPressMoveUpdate].
///
/// Called when a pointer is moving after being held in contact at the same
/// location for a long period of time. Reports the new position and its offset
/// from the original down position.
///
/// See also:
///
///  * [GestureDetector.onLongPressMoveUpdate], which matches this signature.
typedef GestureLongPressMoveUpdateCallback = void Function(LongPressMoveUpdateDetails details);

/// Callback signature for [LongPressGestureRecognizer.onLongPressEnd].
///
/// Called when a pointer stops contacting the screen after a long press
/// gesture was detected. Also reports the position where the pointer stopped
/// contacting the screen.
///
/// See also:
///
///  * [GestureDetector.onLongPressEnd], which matches this signature.
typedef GestureLongPressEndCallback = void Function(LongPressEndDetails details);

/// Details for callbacks that use [GestureLongPressDownCallback].
///
/// See also:
///
///  * [LongPressGestureRecognizer.onLongPressDown], whose callback passes
///    these details.
///  * [LongPressGestureRecognizer.onSecondaryLongPressDown], whose callback
///    passes these details.
///  * [LongPressGestureRecognizer.onTertiaryLongPressDown], whose callback
///    passes these details.
class LongPressDownDetails {
  /// Creates the details for a [GestureLongPressDownCallback].
  ///
  /// If the `localPosition` argument is not specified, it will default to the
  /// global position.
  const LongPressDownDetails({
    this.globalPosition = Offset.zero,
    Offset? localPosition,
    this.kind,
  }) : localPosition = localPosition ?? globalPosition;

  /// The global position at which the pointer contacted the screen.
  final Offset globalPosition;

  /// The kind of the device that initiated the event.
  final PointerDeviceKind? kind;

  /// The local position at which the pointer contacted the screen.
  final Offset localPosition;
}

/// Details for callbacks that use [GestureLongPressStartCallback].
///
/// See also:
///
///  * [LongPressGestureRecognizer.onLongPressStart], which uses [GestureLongPressStartCallback].
///  * [LongPressMoveUpdateDetails], the details for [GestureLongPressMoveUpdateCallback]
///  * [LongPressEndDetails], the details for [GestureLongPressEndCallback].
class LongPressStartDetails {
  /// Creates the details for a [GestureLongPressStartCallback].
  const LongPressStartDetails({
    this.globalPosition = Offset.zero,
    Offset? localPosition,
  }) : localPosition = localPosition ?? globalPosition;

  /// The global position at which the pointer initially contacted the screen.
  final Offset globalPosition;

  /// The local position at which the pointer initially contacted the screen.
  final Offset localPosition;
}

/// Details for callbacks that use [GestureLongPressMoveUpdateCallback].
///
/// See also:
///
///  * [LongPressGestureRecognizer.onLongPressMoveUpdate], which uses [GestureLongPressMoveUpdateCallback].
///  * [LongPressEndDetails], the details for [GestureLongPressEndCallback]
///  * [LongPressStartDetails], the details for [GestureLongPressStartCallback].
class LongPressMoveUpdateDetails {
  /// Creates the details for a [GestureLongPressMoveUpdateCallback].
  const LongPressMoveUpdateDetails({
    this.globalPosition = Offset.zero,
    Offset? localPosition,
    this.offsetFromOrigin = Offset.zero,
    Offset? localOffsetFromOrigin,
  }) : localPosition = localPosition ?? globalPosition,
       localOffsetFromOrigin = localOffsetFromOrigin ?? offsetFromOrigin;

  /// The global position of the pointer when it triggered this update.
  final Offset globalPosition;

  /// The local position of the pointer when it triggered this update.
  final Offset localPosition;

  /// A delta offset from the point where the long press drag initially contacted
  /// the screen to the point where the pointer is currently located (the
  /// present [globalPosition]) when this callback is triggered.
  final Offset offsetFromOrigin;

  /// A local delta offset from the point where the long press drag initially contacted
  /// the screen to the point where the pointer is currently located (the
  /// present [localPosition]) when this callback is triggered.
  final Offset localOffsetFromOrigin;
}

/// Details for callbacks that use [GestureLongPressEndCallback].
///
/// See also:
///
///  * [LongPressGestureRecognizer.onLongPressEnd], which uses [GestureLongPressEndCallback].
///  * [LongPressMoveUpdateDetails], the details for [GestureLongPressMoveUpdateCallback].
///  * [LongPressStartDetails], the details for [GestureLongPressStartCallback].
class LongPressEndDetails {
  /// Creates the details for a [GestureLongPressEndCallback].
  const LongPressEndDetails({
    this.globalPosition = Offset.zero,
    Offset? localPosition,
    this.velocity = Velocity.zero,
  }) : localPosition = localPosition ?? globalPosition;

  /// The global position at which the pointer lifted from the screen.
  final Offset globalPosition;

  /// The local position at which the pointer contacted the screen.
  final Offset localPosition;

  /// The pointer's velocity when it stopped contacting the screen.
  ///
  /// Defaults to zero if not specified in the constructor.
  final Velocity velocity;
}

/// Recognizes when the user has pressed down at the same location for a long
/// period of time.
///
/// The gesture must not deviate in position from its touch down point for 500ms
/// until it's recognized. Once the gesture is accepted, the finger can be
/// moved, triggering [onLongPressMoveUpdate] callbacks, unless the
/// [postAcceptSlopTolerance] constructor argument is specified.
///
/// [LongPressGestureRecognizer] may compete on pointer events of
/// [kPrimaryButton], [kSecondaryButton], and/or [kTertiaryButton] if at least
/// one corresponding callback is non-null. If it has no callbacks, it is a no-op.
class LongPressGestureRecognizer extends PrimaryPointerGestureRecognizer {
  /// Creates a long-press gesture recognizer.
  ///
  /// Consider assigning the [onLongPressStart] callback after creating this
  /// object.
  ///
  /// The [postAcceptSlopTolerance] argument can be used to specify a maximum
  /// allowed distance for the gesture to deviate from the starting point once
  /// the long press has triggered. If the gesture deviates past that point,
  /// subsequent callbacks ([onLongPressMoveUpdate], [onLongPressUp],
  /// [onLongPressEnd]) will stop. Defaults to null, which means the gesture
  /// can be moved without limit once the long press is accepted.
  ///
  /// The [duration] argument can be used to overwrite the default duration
  /// after which the long press will be recognized.
  ///
  /// {@macro flutter.gestures.tap.TapGestureRecognizer.allowedButtonsFilter}
  ///
  /// {@macro flutter.gestures.GestureRecognizer.supportedDevices}
  LongPressGestureRecognizer({
    Duration? duration,
    super.postAcceptSlopTolerance = null,
    super.supportedDevices,
    super.debugOwner,
    AllowedButtonsFilter? allowedButtonsFilter,
  }) : super(
         deadline: duration ?? kLongPressTimeout,
         allowedButtonsFilter: allowedButtonsFilter ?? _defaultButtonAcceptBehavior,
       );

  bool _longPressAccepted = false;
  OffsetPair? _longPressOrigin;
  // The buttons sent by `PointerDownEvent`. If a `PointerMoveEvent` comes with a
  // different set of buttons, the gesture is canceled.
  int? _initialButtons;

  // Accept the input if, and only if, a single button is pressed.
  static bool _defaultButtonAcceptBehavior(int buttons) =>
      buttons == kPrimaryButton ||
      buttons == kSecondaryButton ||
      buttons == kTertiaryButton;

  /// Called when a pointer has contacted the screen at a particular location
  /// with a primary button, which might be the start of a long-press.
  ///
  /// This triggers after the pointer down event.
  ///
  /// If this recognizer doesn't win the arena, [onLongPressCancel] is called
  /// next. Otherwise, [onLongPressStart] is called next.
  ///
  /// See also:
  ///
  ///  * [kPrimaryButton], the button this callback responds to.
  ///  * [onSecondaryLongPressDown], a similar callback but for a secondary button.
  ///  * [onTertiaryLongPressDown], a similar callback but for a tertiary button.
  ///  * [LongPressDownDetails], which is passed as an argument to this callback.
  ///  * [GestureDetector.onLongPressDown], which exposes this callback in a widget.
  GestureLongPressDownCallback? onLongPressDown;

  /// Called when a pointer that previously triggered [onLongPressDown] will
  /// not end up causing a long-press.
  ///
  /// This triggers once the gesture loses the arena if [onLongPressDown] has
  /// previously been triggered.
  ///
  /// If this recognizer wins the arena, [onLongPressStart] and [onLongPress]
  /// are called instead.
  ///
  /// If the gesture is deactivated due to [postAcceptSlopTolerance] having
  /// been exceeded, this callback will not be called, since the gesture will
  /// have already won the arena at that point.
  ///
  /// See also:
  ///
  ///  * [kPrimaryButton], the button this callback responds to.
  GestureLongPressCancelCallback? onLongPressCancel;

  /// Called when a long press gesture by a primary button has been recognized.
  ///
  /// This is equivalent to (and is called immediately after) [onLongPressStart].
  /// The only difference between the two is that this callback does not
  /// contain details of the position at which the pointer initially contacted
  /// the screen.
  ///
  /// See also:
  ///
  ///  * [kPrimaryButton], the button this callback responds to.
  GestureLongPressCallback? onLongPress;

  /// Called when a long press gesture by a primary button has been recognized.
  ///
  /// This is equivalent to (and is called immediately before) [onLongPress].
  /// The only difference between the two is that this callback contains
  /// details of the position at which the pointer initially contacted the
  /// screen, whereas [onLongPress] does not.
  ///
  /// See also:
  ///
  ///  * [kPrimaryButton], the button this callback responds to.
  ///  * [LongPressStartDetails], which is passed as an argument to this callback.
  GestureLongPressStartCallback? onLongPressStart;

  /// Called when moving after the long press by a primary button is recognized.
  ///
  /// See also:
  ///
  ///  * [kPrimaryButton], the button this callback responds to.
  ///  * [LongPressMoveUpdateDetails], which is passed as an argument to this
  ///    callback.
  GestureLongPressMoveUpdateCallback? onLongPressMoveUpdate;

  /// Called when the pointer stops contacting the screen after a long-press
  /// by a primary button.
  ///
  /// This is equivalent to (and is called immediately after) [onLongPressEnd].
  /// The only difference between the two is that this callback does not
  /// contain details of the state of the pointer when it stopped contacting
  /// the screen.
  ///
  /// See also:
  ///
  ///  * [kPrimaryButton], the button this callback responds to.
  GestureLongPressUpCallback? onLongPressUp;

  /// Called when the pointer stops contacting the screen after a long-press
  /// by a primary button.
  ///
  /// This is equivalent to (and is called immediately before) [onLongPressUp].
  /// The only difference between the two is that this callback contains
  /// details of the state of the pointer when it stopped contacting the
  /// screen, whereas [onLongPressUp] does not.
  ///
  /// See also:
  ///
  ///  * [kPrimaryButton], the button this callback responds to.
  ///  * [LongPressEndDetails], which is passed as an argument to this
  ///    callback.
  GestureLongPressEndCallback? onLongPressEnd;

  /// Called when a pointer has contacted the screen at a particular location
  /// with a secondary button, which might be the start of a long-press.
  ///
  /// This triggers after the pointer down event.
  ///
  /// If this recognizer doesn't win the arena, [onSecondaryLongPressCancel] is
  /// called next. Otherwise, [onSecondaryLongPressStart] is called next.
  ///
  /// See also:
  ///
  ///  * [kSecondaryButton], the button this callback responds to.
  ///  * [onLongPressDown], a similar callback but for a primary button.
  ///  * [onTertiaryLongPressDown], a similar callback but for a tertiary button.
  ///  * [LongPressDownDetails], which is passed as an argument to this callback.
  ///  * [GestureDetector.onSecondaryLongPressDown], which exposes this callback
  ///    in a widget.
  GestureLongPressDownCallback? onSecondaryLongPressDown;

  /// Called when a pointer that previously triggered [onSecondaryLongPressDown]
  /// will not end up causing a long-press.
  ///
  /// This triggers once the gesture loses the arena if
  /// [onSecondaryLongPressDown] has previously been triggered.
  ///
  /// If this recognizer wins the arena, [onSecondaryLongPressStart] and
  /// [onSecondaryLongPress] are called instead.
  ///
  /// If the gesture is deactivated due to [postAcceptSlopTolerance] having
  /// been exceeded, this callback will not be called, since the gesture will
  /// have already won the arena at that point.
  ///
  /// See also:
  ///
  ///  * [kSecondaryButton], the button this callback responds to.
  GestureLongPressCancelCallback? onSecondaryLongPressCancel;

  /// Called when a long press gesture by a secondary button has been
  /// recognized.
  ///
  /// This is equivalent to (and is called immediately after)
  /// [onSecondaryLongPressStart]. The only difference between the two is that
  /// this callback does not contain details of the position at which the
  /// pointer initially contacted the screen.
  ///
  /// See also:
  ///
  ///  * [kSecondaryButton], the button this callback responds to.
  GestureLongPressCallback? onSecondaryLongPress;

  /// Called when a long press gesture by a secondary button has been recognized.
  ///
  /// This is equivalent to (and is called immediately before)
  /// [onSecondaryLongPress]. The only difference between the two is that this
  /// callback contains details of the position at which the pointer initially
  /// contacted the screen, whereas [onSecondaryLongPress] does not.
  ///
  /// See also:
  ///
  ///  * [kSecondaryButton], the button this callback responds to.
  ///  * [LongPressStartDetails], which is passed as an argument to this
  ///    callback.
  GestureLongPressStartCallback? onSecondaryLongPressStart;

  /// Called when moving after the long press by a secondary button is
  /// recognized.
  ///
  /// See also:
  ///
  ///  * [kSecondaryButton], the button this callback responds to.
  ///  * [LongPressMoveUpdateDetails], which is passed as an argument to this
  ///    callback.
  GestureLongPressMoveUpdateCallback? onSecondaryLongPressMoveUpdate;

  /// Called when the pointer stops contacting the screen after a long-press by
  /// a secondary button.
  ///
  /// This is equivalent to (and is called immediately after)
  /// [onSecondaryLongPressEnd]. The only difference between the two is that
  /// this callback does not contain details of the state of the pointer when
  /// it stopped contacting the screen.
  ///
  /// See also:
  ///
  ///  * [kSecondaryButton], the button this callback responds to.
  GestureLongPressUpCallback? onSecondaryLongPressUp;

  /// Called when the pointer stops contacting the screen after a long-press by
  /// a secondary button.
  ///
  /// This is equivalent to (and is called immediately before)
  /// [onSecondaryLongPressUp]. The only difference between the two is that
  /// this callback contains details of the state of the pointer when it
  /// stopped contacting the screen, whereas [onSecondaryLongPressUp] does not.
  ///
  /// See also:
  ///
  ///  * [kSecondaryButton], the button this callback responds to.
  ///  * [LongPressEndDetails], which is passed as an argument to this callback.
  GestureLongPressEndCallback? onSecondaryLongPressEnd;

  /// Called when a pointer has contacted the screen at a particular location
  /// with a tertiary button, which might be the start of a long-press.
  ///
  /// This triggers after the pointer down event.
  ///
  /// If this recognizer doesn't win the arena, [onTertiaryLongPressCancel] is
  /// called next. Otherwise, [onTertiaryLongPressStart] is called next.
  ///
  /// See also:
  ///
  ///  * [kTertiaryButton], the button this callback responds to.
  ///  * [onLongPressDown], a similar callback but for a primary button.
  ///  * [onSecondaryLongPressDown], a similar callback but for a secondary button.
  ///  * [LongPressDownDetails], which is passed as an argument to this callback.
  ///  * [GestureDetector.onTertiaryLongPressDown], which exposes this callback
  ///    in a widget.
  GestureLongPressDownCallback? onTertiaryLongPressDown;

  /// Called when a pointer that previously triggered [onTertiaryLongPressDown]
  /// will not end up causing a long-press.
  ///
  /// This triggers once the gesture loses the arena if
  /// [onTertiaryLongPressDown] has previously been triggered.
  ///
  /// If this recognizer wins the arena, [onTertiaryLongPressStart] and
  /// [onTertiaryLongPress] are called instead.
  ///
  /// If the gesture is deactivated due to [postAcceptSlopTolerance] having
  /// been exceeded, this callback will not be called, since the gesture will
  /// have already won the arena at that point.
  ///
  /// See also:
  ///
  ///  * [kTertiaryButton], the button this callback responds to.
  GestureLongPressCancelCallback? onTertiaryLongPressCancel;

  /// Called when a long press gesture by a tertiary button has been
  /// recognized.
  ///
  /// This is equivalent to (and is called immediately after)
  /// [onTertiaryLongPressStart]. The only difference between the two is that
  /// this callback does not contain details of the position at which the
  /// pointer initially contacted the screen.
  ///
  /// See also:
  ///
  ///  * [kTertiaryButton], the button this callback responds to.
  GestureLongPressCallback? onTertiaryLongPress;

  /// Called when a long press gesture by a tertiary button has been recognized.
  ///
  /// This is equivalent to (and is called immediately before)
  /// [onTertiaryLongPress]. The only difference between the two is that this
  /// callback contains details of the position at which the pointer initially
  /// contacted the screen, whereas [onTertiaryLongPress] does not.
  ///
  /// See also:
  ///
  ///  * [kTertiaryButton], the button this callback responds to.
  ///  * [LongPressStartDetails], which is passed as an argument to this
  ///    callback.
  GestureLongPressStartCallback? onTertiaryLongPressStart;

  /// Called when moving after the long press by a tertiary button is
  /// recognized.
  ///
  /// See also:
  ///
  ///  * [kTertiaryButton], the button this callback responds to.
  ///  * [LongPressMoveUpdateDetails], which is passed as an argument to this
  ///    callback.
  GestureLongPressMoveUpdateCallback? onTertiaryLongPressMoveUpdate;

  /// Called when the pointer stops contacting the screen after a long-press by
  /// a tertiary button.
  ///
  /// This is equivalent to (and is called immediately after)
  /// [onTertiaryLongPressEnd]. The only difference between the two is that
  /// this callback does not contain details of the state of the pointer when
  /// it stopped contacting the screen.
  ///
  /// See also:
  ///
  ///  * [kTertiaryButton], the button this callback responds to.
  GestureLongPressUpCallback? onTertiaryLongPressUp;

  /// Called when the pointer stops contacting the screen after a long-press by
  /// a tertiary button.
  ///
  /// This is equivalent to (and is called immediately before)
  /// [onTertiaryLongPressUp]. The only difference between the two is that
  /// this callback contains details of the state of the pointer when it
  /// stopped contacting the screen, whereas [onTertiaryLongPressUp] does not.
  ///
  /// See also:
  ///
  ///  * [kTertiaryButton], the button this callback responds to.
  ///  * [LongPressEndDetails], which is passed as an argument to this callback.
  GestureLongPressEndCallback? onTertiaryLongPressEnd;

  VelocityTracker? _velocityTracker;

  @override
  bool isPointerAllowed(PointerDownEvent event) {
    switch (event.buttons) {
      case kPrimaryButton:
        if (onLongPressDown == null &&
            onLongPressCancel == null &&
            onLongPressStart == null &&
            onLongPress == null &&
            onLongPressMoveUpdate == null &&
            onLongPressEnd == null &&
            onLongPressUp == null) {
          return false;
        }
      case kSecondaryButton:
        if (onSecondaryLongPressDown == null &&
            onSecondaryLongPressCancel == null &&
            onSecondaryLongPressStart == null &&
            onSecondaryLongPress == null &&
            onSecondaryLongPressMoveUpdate == null &&
            onSecondaryLongPressEnd == null &&
            onSecondaryLongPressUp == null) {
          return false;
        }
      case kTertiaryButton:
        if (onTertiaryLongPressDown == null &&
            onTertiaryLongPressCancel == null &&
            onTertiaryLongPressStart == null &&
            onTertiaryLongPress == null &&
            onTertiaryLongPressMoveUpdate == null &&
            onTertiaryLongPressEnd == null &&
            onTertiaryLongPressUp == null) {
          return false;
        }
      default:
        return false;
    }
    return super.isPointerAllowed(event);
  }

  @override
  void didExceedDeadline() {
    // Exceeding the deadline puts the gesture in the accepted state.
    resolve(GestureDisposition.accepted);
    _longPressAccepted = true;
    super.acceptGesture(primaryPointer!);
    _checkLongPressStart();
  }

  @override
  void handlePrimaryPointer(PointerEvent event) {
    if (!event.synthesized) {
      if (event is PointerDownEvent) {
        _velocityTracker = VelocityTracker.withKind(event.kind);
        _velocityTracker!.addPosition(event.timeStamp, event.localPosition);
      }
      if (event is PointerMoveEvent) {
        assert(_velocityTracker != null);
        _velocityTracker!.addPosition(event.timeStamp, event.localPosition);
      }
    }

    if (event is PointerUpEvent) {
      if (_longPressAccepted) {
        _checkLongPressEnd(event);
      } else {
        // Pointer is lifted before timeout.
        resolve(GestureDisposition.rejected);
      }
      _reset();
    } else if (event is PointerCancelEvent) {
      _checkLongPressCancel();
      _reset();
    } else if (event is PointerDownEvent) {
      // The first touch.
      _longPressOrigin = OffsetPair.fromEventPosition(event);
      _initialButtons = event.buttons;
      _checkLongPressDown(event);
    } else if (event is PointerMoveEvent) {
      if (event.buttons != _initialButtons && !_longPressAccepted) {
        resolve(GestureDisposition.rejected);
        stopTrackingPointer(primaryPointer!);
      } else if (_longPressAccepted) {
        _checkLongPressMoveUpdate(event);
      }
    }
  }

  void _checkLongPressDown(PointerDownEvent event) {
    assert(_longPressOrigin != null);
    final LongPressDownDetails details = LongPressDownDetails(
      globalPosition: _longPressOrigin!.global,
      localPosition: _longPressOrigin!.local,
      kind: getKindForPointer(event.pointer),
    );
    switch (_initialButtons) {
      case kPrimaryButton:
        if (onLongPressDown != null) {
          invokeCallback<void>('onLongPressDown', () => onLongPressDown!(details));
        }
      case kSecondaryButton:
        if (onSecondaryLongPressDown != null) {
          invokeCallback<void>('onSecondaryLongPressDown', () => onSecondaryLongPressDown!(details));
        }
      case kTertiaryButton:
        if (onTertiaryLongPressDown != null) {
          invokeCallback<void>('onTertiaryLongPressDown', () => onTertiaryLongPressDown!(details));
        }
      default:
        assert(false, 'Unhandled button $_initialButtons');
    }
  }

  void _checkLongPressCancel() {
    if (state == GestureRecognizerState.possible) {
      switch (_initialButtons) {
        case kPrimaryButton:
          if (onLongPressCancel != null) {
            invokeCallback<void>('onLongPressCancel', onLongPressCancel!);
          }
        case kSecondaryButton:
          if (onSecondaryLongPressCancel != null) {
            invokeCallback<void>('onSecondaryLongPressCancel', onSecondaryLongPressCancel!);
          }
        case kTertiaryButton:
          if (onTertiaryLongPressCancel != null) {
            invokeCallback<void>('onTertiaryLongPressCancel', onTertiaryLongPressCancel!);
          }
        default:
          assert(false, 'Unhandled button $_initialButtons');
      }
    }
  }

  void _checkLongPressStart() {
    switch (_initialButtons) {
      case kPrimaryButton:
        if (onLongPressStart != null) {
          final LongPressStartDetails details = LongPressStartDetails(
            globalPosition: _longPressOrigin!.global,
            localPosition: _longPressOrigin!.local,
          );
          invokeCallback<void>('onLongPressStart', () => onLongPressStart!(details));
        }
        if (onLongPress != null) {
          invokeCallback<void>('onLongPress', onLongPress!);
        }
      case kSecondaryButton:
        if (onSecondaryLongPressStart != null) {
          final LongPressStartDetails details = LongPressStartDetails(
            globalPosition: _longPressOrigin!.global,
            localPosition: _longPressOrigin!.local,
          );
          invokeCallback<void>('onSecondaryLongPressStart', () => onSecondaryLongPressStart!(details));
        }
        if (onSecondaryLongPress != null) {
          invokeCallback<void>('onSecondaryLongPress', onSecondaryLongPress!);
        }
      case kTertiaryButton:
        if (onTertiaryLongPressStart != null) {
          final LongPressStartDetails details = LongPressStartDetails(
            globalPosition: _longPressOrigin!.global,
            localPosition: _longPressOrigin!.local,
          );
          invokeCallback<void>('onTertiaryLongPressStart', () => onTertiaryLongPressStart!(details));
        }
        if (onTertiaryLongPress != null) {
          invokeCallback<void>('onTertiaryLongPress', onTertiaryLongPress!);
        }
      default:
        assert(false, 'Unhandled button $_initialButtons');
    }
  }

  void _checkLongPressMoveUpdate(PointerEvent event) {
    final LongPressMoveUpdateDetails details = LongPressMoveUpdateDetails(
      globalPosition: event.position,
      localPosition: event.localPosition,
      offsetFromOrigin: event.position - _longPressOrigin!.global,
      localOffsetFromOrigin: event.localPosition - _longPressOrigin!.local,
    );
    switch (_initialButtons) {
      case kPrimaryButton:
        if (onLongPressMoveUpdate != null) {
          invokeCallback<void>('onLongPressMoveUpdate', () => onLongPressMoveUpdate!(details));
        }
      case kSecondaryButton:
        if (onSecondaryLongPressMoveUpdate != null) {
          invokeCallback<void>('onSecondaryLongPressMoveUpdate', () => onSecondaryLongPressMoveUpdate!(details));
        }
      case kTertiaryButton:
        if (onTertiaryLongPressMoveUpdate != null) {
          invokeCallback<void>('onTertiaryLongPressMoveUpdate', () => onTertiaryLongPressMoveUpdate!(details));
        }
      default:
        assert(false, 'Unhandled button $_initialButtons');
    }
  }

  void _checkLongPressEnd(PointerEvent event) {
    final VelocityEstimate? estimate = _velocityTracker!.getVelocityEstimate();
    final Velocity velocity = estimate == null
        ? Velocity.zero
        : Velocity(pixelsPerSecond: estimate.pixelsPerSecond);
    final LongPressEndDetails details = LongPressEndDetails(
      globalPosition: event.position,
      localPosition: event.localPosition,
      velocity: velocity,
    );

    _velocityTracker = null;
    switch (_initialButtons) {
      case kPrimaryButton:
        if (onLongPressEnd != null) {
          invokeCallback<void>('onLongPressEnd', () => onLongPressEnd!(details));
        }
        if (onLongPressUp != null) {
          invokeCallback<void>('onLongPressUp', onLongPressUp!);
        }
      case kSecondaryButton:
        if (onSecondaryLongPressEnd != null) {
          invokeCallback<void>('onSecondaryLongPressEnd', () => onSecondaryLongPressEnd!(details));
        }
        if (onSecondaryLongPressUp != null) {
          invokeCallback<void>('onSecondaryLongPressUp', onSecondaryLongPressUp!);
        }
      case kTertiaryButton:
        if (onTertiaryLongPressEnd != null) {
          invokeCallback<void>('onTertiaryLongPressEnd', () => onTertiaryLongPressEnd!(details));
        }
        if (onTertiaryLongPressUp != null) {
          invokeCallback<void>('onTertiaryLongPressUp', onTertiaryLongPressUp!);
        }
      default:
        assert(false, 'Unhandled button $_initialButtons');
    }
  }

  void _reset() {
    _longPressAccepted = false;
    _longPressOrigin = null;
    _initialButtons = null;
    _velocityTracker = null;
  }

  @override
  void resolve(GestureDisposition disposition) {
    if (disposition == GestureDisposition.rejected) {
      if (_longPressAccepted) {
        // This can happen if the gesture has been canceled. For example when
        // the buttons have changed.
        _reset();
      } else {
        _checkLongPressCancel();
      }
    }
    super.resolve(disposition);
  }

  @override
  void acceptGesture(int pointer) {
    // Winning the arena isn't important here since it may happen from a sweep.
    // Explicitly exceeding the deadline puts the gesture in accepted state.
  }

  @override
  String get debugDescription => 'long press';
}