hardware_scanner_input

A Flutter widget that captures input from HID-mode hardware barcode scanners on Android without surfacing the software keyboard.

Why does this package exist?

Most industrial Android tablets (iData P1, Zebra TC, Honeywell CT, etc.) ship paired with a hardware barcode scanner running in HID / Focus mode. In that mode the scanner is not a USB serial device — it injects each scanned character into the currently focused Android InputConnection via commitText(), then sends an Enter key. The only way to receive scans is to keep a focused text input alive.

Naively dropping a TextField on the page is wrong:

1. The on-screen keyboard pops up, covering your UI.
2. Some scanner models omit the trailing Enter — onSubmitted never fires and the value is stuck in the controller.

HardwareScannerInput fixes both, in 110 lines:

• keyboardType: TextInputType.none keeps the soft keyboard hidden while the field retains a live InputConnection.
• A configurable silence timeout (default 150 ms) flushes the buffered text once the scanner stops streaming characters, with or without Enter.
• The text is rendered transparent and 1 px tall so the widget stacks invisibly behind your real scan-indicator UI.

Install

flutter pub add hardware_scanner_input

Usage

Stack it behind your visual scan indicator:

import 'package:flutter/material.dart';
import 'package:hardware_scanner_input/hardware_scanner_input.dart';

class ScanStep extends StatelessWidget {
  const ScanStep({super.key});

  @override
  Widget build(BuildContext context) {
    return Stack(
      fit: StackFit.expand,
      children: [
        HardwareScannerInput(
          onScanned: (value) => debugPrint('scanned: $value'),
        ),
        const IgnorePointer(child: _ScanReadyIndicator()),
      ],
    );
  }
}

For a full-page scan screen, place HardwareScannerInput as the bottom-most child of the page Stack so it always holds focus.

API

Parameter	Type	Default	Notes
onScanned	void Function(String)	—	Fires once per complete scan. Trimmed; empty scans are dropped.
focusNode	FocusNode?	null	Inject your own when managing focus yourself.
autofocus	bool	true	Whether the field claims focus on insert.
silenceTimeout	Duration	150 ms	How long to wait after the last character before flushing.

How it works under the hood

Scanner trigger
   │
   ▼
Android InputMethodManager.commitText()
   │
   ▼
TextField.onChanged (per character)
   │
   └─► reset 150 ms timer ─► onSubmitted (Enter received)? flush.
                          └─► timer fires? flush.

TextInputType.none maps to TYPE_NULL on the Android side, which is the documented way to suppress the IME while keeping a working InputConnection. Tested on Android 11–14.

Testing

The widget is exercised with WidgetTester.enterText and the test pump clock — see test/hardware_scanner_input_test.dart.

flutter test

Example app

The example/ directory contains a runnable demo screen.

cd example
flutter run

License

MIT — see LICENSE.