lib/ui/key.dart

// Copyright 2013 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.

// @dart = 2.12

part of dart.ui;

/// The type of a key event.
// Must match the KeyEventType enum in ui/window/key_data.h.
enum KeyEventType {
  /// The key is pressed.
  down,

  /// The key is released.
  up,

  /// The key is held, causing a repeated key input.
  repeat,
}

/// Information about a key event.
class KeyData {
  /// Creates an object that represents a key event.
  const KeyData({
    required this.timeStamp,
    required this.type,
    required this.physical,
    required this.logical,
    required this.character,
    required this.synthesized,
  });

  /// Time of event dispatch, relative to an arbitrary timeline.
  ///
  /// For synthesized events, the [timeStamp] might not be the actual time that
  /// the key press or release happens.
  final Duration timeStamp;

  /// The type of the event.
  final KeyEventType type;

  /// The key code for the physical key that has changed.
  final int physical;

  /// The key code for the logical key that has changed.
  final int logical;

  /// Character input from the event.
  ///
  /// Ignored for up events.
  final String? character;

  /// If [synthesized] is true, this event does not correspond to a native event.
  ///
  /// Although most of Flutter's keyboard events are transformed from native
  /// events, some events are not based on native events, and are synthesized
  /// only to conform Flutter's key event model (as documented in
  /// the `HardwareKeyboard` class in the framework).
  ///
  /// For example, some key downs or ups might be lost when the window loses
  /// focus. Some platforms provides ways to query whether a key is being held.
  /// If the embedder detects an inconsistancy between its internal record and
  /// the state returned by the system, the embedder will synthesize a
  /// corresponding event to synchronize the state without breaking the event
  /// model.
  ///
  /// As another example, macOS treats CapsLock in a special way by sending
  /// down and up events at the down of alterate presses to indicate the
  /// direction in which the lock is toggled instead of that the physical key is
  /// going. A macOS embedder should normalize the behavior by converting a
  /// native down event into a down event followed immediately by a synthesized
  /// up event, and the native up event also into a down event followed
  /// immediately by a synthesized up event.
  ///
  /// Synthesized events do not have a trustworthy [timeStamp], and should not be
  /// processed as if the key actually went down or up at the time of the
  /// callback.
  ///
  /// [KeyRepeatEvent] is never synthesized.
  final bool synthesized;

  @override
  String toString() => 'KeyData(type: ${_typeToString(type)}, physical: 0x${physical.toRadixString(16)}, '
    'logical: 0x${logical.toRadixString(16)}, character: $character)';

  /// Returns a complete textual description of the information in this object.
  String toStringFull() {
    return '$runtimeType('
            'type: ${_typeToString(type)}, '
            'timeStamp: $timeStamp, '
            'physical: 0x${physical.toRadixString(16)}, '
            'logical: 0x${logical.toRadixString(16)}, '
            'character: $character, '
            'synthesized: $synthesized'
           ')';
  }

  static String _typeToString(KeyEventType type) {
    switch (type) {
      case KeyEventType.up:
        return 'up';
      case KeyEventType.down:
        return 'down';
      case KeyEventType.repeat:
        return 'repeat';
    }
  }
}