On Android, KeyboardListener catches software keyboard input.

[asci-00]

Steps to reproduce

Our app has a function that operates by distinguishing between hardware (bluetooth) keyboard input and software keyboard input for TextField.
While searching for the API provided by Flutter to implement this, I came across the KeyboardListener widget description below.

/// ..in keyboard_listener.dart
/// A [KeyboardListener] is useful for listening to key events and
/// hardware buttons that are represented as keys. Typically used by games and
/// other apps that use keyboards for purposes other than text entry.

/// ..in hardware_keyboard.dart
/// The [KeyEvent] provides a universal model for key event information from a
/// hardware keyboard across platforms.

From the above explanation, I understood that KeyboardListener only recognizes hardware keys.

We applied this to our project because we thought it suited our requirements, but the actual behavior was different from what we expected.

In fact, when we run the app with the code below using KeyboardListenerd, the backspace (if there is no string to delete) and enter (textfield property - textInputAction: newline) keys entered on the software keyboard are detected as if backspace or enter were pressed on the hardware keyboard.
Additionally, we were unable to determine whether the input was software or hardware from the detected results.

Does this mean I misunderstood the document? or is this not the widget provided with this intention?
I'm not sure if this is a bug, but if this is the intended result, it would be helpful if the documentation for KeyboardListener or KeyEvent was a bit nicer.
Also, if there is a way to implement the above requirements, please kindly let me know.

(I tested it on Samsung Keyboard and GBoard, and the results were different. I used a Korean/English keyboard, and it was also different when I typed in Korean and English. - test os: android - )

Expected results

Key input from the software keyboard is not detected in the Keyboardlistener onKeyEvent.

Actual results

Depending on the keyboard type / input language / key type, onKeyEvent is called for some software keyboard inputs.

Code sample

class Home extends StatefulWidget {
  const Home({super.key});

  @override
  State<Home> createState() => _HomeState();
}

class _HomeState extends State<Home> {
  final FocusNode focusNode = FocusNode();

  @override
  void dispose() {
    focusNode.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text("keyboard listener")),
      body: Column(crossAxisAlignment: CrossAxisAlignment.center, children: [
        KeyboardListener(
          focusNode: focusNode,
          onKeyEvent: print,
          child: const TextField(textInputAction: TextInputAction.newline),
        ),
      ]),
    );
  }
}

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[darshankawar]

@asci-00
Can you check if this resembles your case or not ?
Also check if this is related #44681

[asci-00]

Hi @darshankawar
Well, I don't know if it's completely unrelated, but
#51478 issue is an issue where the OnScreen keyboard (the software keyboard I wrote above) is opened due to input from the hardware keyboard.
#44681 issue is also related to this, and seems to be a question about how to not raise the keyboard when the textfield has focus. It may be related internally, but it seems to be a different problem than mine.

[darshankawar]

Thanks for the update. Check if this applies to your case as well or not.

[LongCatIsLooong]

The Android InputConnection API allows a software keyboard to send a keypress as a KeyEvent (https://developer.android.com/reference/android/view/inputmethod/InputConnection#sendKeyEvent(android.view.KeyEvent)).

Usually keyboards do that for backspace because sometimes if a text field is already empty you want to move the focus to the previous field. Flutter currently does not distinguish KeyEvents emitted by this method call and KeyEvents generated by physical keyboards.

[asci-00]

@darshankawar I'm not sure if I understand the problem correctly. I think the issue is that the hardware keyboard operates differently depending on the mobile device (s9 / pixel) when using RawKeyboardListener.
It seems like a similar problem to some extent, but the point of my issue is that keypress from the “software keyboard” are detected by KeyboardListener, so it seems like a different issue. Please let me know if I misunderstood the issue

[asci-00]

@LongCatIsLooong thank you for the reply.
This is an area I don't know, so I'd like to ask. Is the entity that raises KeyEvent using InputConnection the software keyboard? ex) GBoard / Samsung Keyboard
Also, I wonder if the Enter key, other than backspace, also applies.
If so, I am curious as to whether it is possible to distinguish the KeyEvent in Flutter (at a low level) and whether it plans to support the function to distinguish it.
If it is not supported, is there any way to implement the requirements I mentioned?

[darshankawar]

@asci-00
Check if below issues help in your case or not:

#142882
#131510

[LongCatIsLooong]

@LongCatIsLooong thank you for the reply. This is an area I don't know, so I'd like to ask. Is the entity that raises KeyEvent using InputConnection the software keyboard? ex) GBoard / Samsung Keyboard Also, I wonder if the Enter key, other than backspace, also applies. If so, I am curious as to whether it is possible to distinguish the KeyEvent in Flutter (at a low level) and whether it plans to support the function to distinguish it. If it is not supported, is there any way to implement the requirements I mentioned?

Yes. Software keyboards (Gboard / Samsung Keyboard) can choose to send certain key presses as hardware key events (for reasons stated above). They can even send "A" as a key event if they so choose.

If so, I am curious as to whether it is possible to distinguish the KeyEvent in Flutter

I believe this is possible on Android because they have separate call paths: https://github.com/flutter/engine/blob/c6fecf65fbf385c5e9168c5b40526c9ae998045b/shell/platform/android/io/flutter/plugin/editing/InputConnectionAdaptor.java#L285-L287

But this may not be possible on other platforms. And editors typically don't need such information.

Our app has a function that operates by distinguishing between hardware (bluetooth) keyboard input and software keyboard input

This sounds like a relatively niche use case, could you elaborate?

[asci-00]

@LongCatIsLooong Sorry for the late reply. 😓
To explain part of the function, you can set the enter (submit) action of the software keyboard and the enter action of the hardware keyboard separately in the textfield.
If you press enter on a hardware keyboard, the default action branches into two actions depending on the value you set.

1. When press enter, newline
2. When press enter, send
   However, the software keyboard must always be newline.

However, flutter cannot check whether the hardware keyboard is connected and
In the case of Samsung keyboards, due to an issue, the software keyboard comes up even when the hardware keyboard is connected unless the user configures it separately.
Therefore, we need to know whether the Enter KeyEvent caught by KeyboardListener occurred in hardware or software, but there is no way to distinguish between them. This is the current problem situation.

[darshankawar]

Keeping the issue open and labeling for team's tracking.

[LongCatIsLooong]

Is https://main-api.flutter.dev/flutter/widgets/EditableText/onEditingComplete.html what you are looking for?

[asci-00]

@LongCatIsLooong
Could you please explain in more detail?
When I checked by applying onEditingComplete, it seems that both hardware Enter and software Enter are not distinguished and are caught in callback.

[LongCatIsLooong]

Ah indeed it does, but it's disabled for multiline: https://github.com/flutter/engine/blob/557a4c622617c6c0f66b604669d14d11b8aa1cbe/shell/platform/android/io/flutter/plugin/editing/InputConnectionAdaptor.java#L304

This is a bit strange. I don't think a hardware key-presses should trigger performEditorAction automatically.

[LongCatIsLooong]

Tentatively marked this issue as P3. However, if you would like to see this issue fixed sooner, you are welcome to open a pull request to remove the logic that is causing this issue.