mobile_scanner.dart
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import 'dart:async';
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:mobile_scanner/src/mobile_scanner_controller.dart';
import 'package:mobile_scanner/src/objects/barcode_capture.dart';
import 'package:mobile_scanner/src/objects/mobile_scanner_arguments.dart';
/// The [MobileScanner] widget displays a live camera preview.
class MobileScanner extends StatefulWidget {
/// The controller that manages the barcode scanner.
final MobileScannerController controller;
/// The [BoxFit] for the camera preview.
///
/// Defaults to [BoxFit.cover].
final BoxFit fit;
/// The function that signals when new barcodes were detected by the [controller].
final void Function(BarcodeCapture barcodes) onBarcodeDetected;
/// The function that signals when the barcode scanner is restarted,
/// due to coming back to the foreground.
final void Function(MobileScannerArguments? arguments)? onScannerRestarted;
/// The function that builds a placeholder widget when the scanner
/// is not yet displaying its camera preview.
///
/// If this is null, a black [ColoredBox] is used as placeholder.
final Widget Function(BuildContext, Widget?)? placeholderBuilder;
/// Create a new [MobileScanner] using the provided [controller]
/// and [onBarcodeDetected] callback.
const MobileScanner({
required this.controller,
this.fit = BoxFit.cover,
required this.onBarcodeDetected,
this.onScannerRestarted,
this.placeholderBuilder,
super.key,
});
@override
State<MobileScanner> createState() => _MobileScannerState();
}
class _MobileScannerState extends State<MobileScanner>
with WidgetsBindingObserver {
/// The subscription that listens to barcode detection.
StreamSubscription<BarcodeCapture>? _barcodesSubscription;
/// Whether the controller should resume
/// when the application comes back to the foreground.
bool _resumeFromBackground = false;
/// Restart a previously paused scanner.
void _restartScanner() {
widget.controller.start().then((arguments) {
widget.onScannerRestarted?.call(arguments);
}).catchError((error) {
// The scanner somehow failed to restart.
// There is no way to recover from this, so do nothing.
});
}
@override
void initState() {
super.initState();
WidgetsBinding.instance.addObserver(this);
_barcodesSubscription = widget.controller.barcodes.listen(
widget.onBarcodeDetected,
);
}
@override
void didChangeAppLifecycleState(AppLifecycleState state) {
// App state changed before the controller was initialized.
if (widget.controller.isStarting) {
return;
}
switch (state) {
case AppLifecycleState.resumed:
_resumeFromBackground = false;
_restartScanner();
break;
case AppLifecycleState.paused:
_resumeFromBackground = true;
break;
case AppLifecycleState.inactive:
if (!_resumeFromBackground) {
widget.controller.stop();
}
break;
case AppLifecycleState.detached:
break;
}
}
@override
Widget build(BuildContext context) {
return ValueListenableBuilder<MobileScannerArguments?>(
valueListenable: widget.controller.startArguments,
builder: (context, value, child) {
if (value == null) {
return widget.placeholderBuilder?.call(context, child) ??
const ColoredBox(color: Colors.black);
}
return ClipRect(
child: LayoutBuilder(
builder: (_, constraints) {
return SizedBox.fromSize(
size: constraints.biggest,
child: FittedBox(
fit: widget.fit,
child: SizedBox(
width: value.size.width,
height: value.size.height,
child: kIsWeb
? HtmlElementView(viewType: value.webId!)
: Texture(textureId: value.textureId!),
),
),
);
},
),
);
},
);
}
@override
void dispose() {
WidgetsBinding.instance.removeObserver(this);
_barcodesSubscription?.cancel();
super.dispose();
}
}