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Summary

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For some time now (years), Flutter has had two key event systems implemented. The new system reached parity with the old platform-specific raw key event system, and the raw system has been deprecated.

Context

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In the original key event subsystem, handling each platform's quirks in the framework and in client apps caused overly complex code, and the old system didn't properly represent the true state of key events on the system.

The legacy API RawKeyboard has been deprecated and will be removed in the future. The HardwareKeyboard and KeyEvent APIs replace this legacy API. An example of this change is FocusNode.onKeyEvent replacing FocusNode.onKey.

The behavior of RawKeyboard provided a less unified and less regular event model than HardwareKeyboard does. Consider the following examples:

  • Down events were not always matched with an up event, and vice versa (the set of pressed keys was silently updated).
  • The logical key of the down event was not always the same as that of the up event.
  • Down events and repeat events were not easily distinguishable (had to be tracked manually).
  • Lock modes (such as CapsLock) only had their "enabled" state recorded. There was no way to acquire their pressed state.

So, the new KeyEvent/HardwareKeyboard-based system was born and, to minimize breaking changes, was implemented in parallel with the old system with the intention of eventually deprecating the raw system. That time has arrived, and application developers should migrate their code to avoid breaking changes that will occur when the deprecated APIs are removed.

Description of change

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Below are the APIs that have been deprecated.

Deprecated APIs that have an equivalent

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APIs that have been discontinued

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These APIs are no longer needed once there is only one key event system, or their functionality is no longer offered.

Migration guide

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The Flutter framework libraries have already been migrated. If your code uses any of the classes or methods listed in the previous section, migrate to these new APIs.

Migrating your code that uses RawKeyEvent

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For the most part, there are equivalent KeyEvent APIs available for all of the RawKeyEvent APIs.

Some APIs relating to platform specific information contained in RawKeyEventData objects or their subclasses have been removed and are no longer supported. One exception is that RawKeyEventDataAndroid.eventSource information is accessible now as KeyEvent.deviceType in a more platform independent form.

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If the legacy code used the RawKeyEvent.isKeyPressed, RawKeyEvent.isControlPressed, RawKeyEvent.isShiftPressed, RawKeyEvent.isAltPressed, or RawKeyEvent.isMetaPressed APIs, there are now equivalent functions on the HardwareKeyboard singleton instance, but are not available on [KeyEvent]. RawKeyEvent.isKeyPressed is available as HardwareKeyboard.isLogicalKeyPressed.

Before:

dart
KeyEventResult _handleKeyEvent(RawKeyEvent keyEvent) {
  if (keyEvent.isControlPressed ||
      keyEvent.isShiftPressed ||
      keyEvent.isAltPressed ||
      keyEvent.isMetaPressed) {
    print('Modifier pressed: $keyEvent');
  }
  if (keyEvent.isKeyPressed(LogicalKeyboardKey.keyA)) {
    print('Key A pressed.');
  }
  return KeyEventResult.ignored;
}

After:

dart
KeyEventResult _handleKeyEvent(KeyEvent _) {
  if (HardwareKeyboard.instance.isControlPressed ||
      HardwareKeyboard.instance.isShiftPressed ||
      HardwareKeyboard.instance.isAltPressed ||
      HardwareKeyboard.instance.isMetaPressed) {
    print('Modifier pressed: $keyEvent');
  }
  if (HardwareKeyboard.instance.isLogicalKeyPressed(LogicalKeyboardKey.keyA)) {
    print('Key A pressed.');
  }
  return KeyEventResult.ignored;
}

Setting onKey for focus

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If the legacy code was using the Focus.onKey, FocusScope.onKey, FocusNode.onKey, or FocusScopeNode.onKey parameters, then there is an equivalent Focus.onKeyEvent, FocusScope.onKeyEvent, FocusNode.onKeyEvent, or FocusScopeNode.onKeyEvent parameter that supplies KeyEvents instead of RawKeyEvents.

Before:

dart
Widget build(BuildContext context) {
  return Focus(
    onKey: (RawKeyEvent keyEvent) {
      print('Key event: $keyEvent');
      return KeyEventResult.ignored;
    }
    child: child,
  );
}

After:

dart
Widget build(BuildContext context) {
  return Focus(
    onKeyEvent: (KeyEvent keyEvent) {
      print('Key event: $keyEvent');
      return KeyEventResult.ignored;
    }
    child: child,
  );
}

Repeat key event handling

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If you were relying on the RawKeyEvent.repeat attribute to determine if a key was a repeated key event, that has now been separated into a separate KeyRepeatEvent type.

Before:

dart
KeyEventResult _handleKeyEvent(RawKeyEvent keyEvent) {
  if (keyEvent is RawKeyDownEvent) {
    print('Key down: ${keyEvent.data.logicalKey.keyLabel}(${keyEvent.repeat ? ' (repeated)' : ''})');
  }
  return KeyEventResult.ignored;
}

After:

dart
KeyEventResult _handleKeyEvent(KeyEvent _) {
  if (keyEvent is KeyDownEvent || keyEvent is KeyRepeatEvent) {
    print('Key down: ${keyEvent.logicalKey.keyLabel}(${keyEvent is KeyRepeatEvent ? ' (repeated)' : ''})');
  }
  return KeyEventResult.ignored;
}

Though it is not a subclass of KeyDownEvent, a KeyRepeatEvent is also a key down event. Don't assume that keyEvent is! KeyDownEvent only allows key up events. Check both KeyDownEvent and KeyRepeatEvent.

Timeline

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Landed in version: 3.18.0-7.0.pre
In stable release: 3.19.0

References

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Replacement API documentation:

Relevant issues:

Relevant PRs:

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