add helper widgets for the example

+import 'package:flutter/material.dart';
+import 'package:image_picker/image_picker.dart';
+import 'package:mobile_scanner/mobile_scanner.dart';
+
+class AnalyzeImageFromGalleryButton extends StatelessWidget {
+  const AnalyzeImageFromGalleryButton({required this.controller, super.key});
+
+  final MobileScannerController controller;
+
+  @override
+  Widget build(BuildContext context) {
+    return IconButton(
+      color: Colors.white,
+      icon: const Icon(Icons.image),
+      iconSize: 32.0,
+      onPressed: () async {
+        final ImagePicker picker = ImagePicker();
+
+        final XFile? image = await picker.pickImage(
+          source: ImageSource.gallery,
+        );
+
+        if (image == null) {
+          return;
+        }
+
+        final BarcodeCapture? barcodes = await controller.analyzeImage(
+          image.path,
+        );
+
+        if (!context.mounted) {
+          return;
+        }
+
+        final SnackBar snackbar = barcodes != null
+            ? const SnackBar(
+                content: Text('Barcode found!'),
+                backgroundColor: Colors.green,
+              )
+            : const SnackBar(
+                content: Text('No barcode found!'),
+                backgroundColor: Colors.red,
+              );
+
+        ScaffoldMessenger.of(context).showSnackBar(snackbar);
+      },
+    );
+  }
+}
+
+class StartStopMobileScannerButton extends StatelessWidget {
+  const StartStopMobileScannerButton({required this.controller, super.key});
+
+  final MobileScannerController controller;
+
+  @override
+  Widget build(BuildContext context) {
+    return ValueListenableBuilder(
+      valueListenable: controller,
+      builder: (context, state, child) {
+        if (!state.isInitialized || !state.isRunning) {
+          return IconButton(
+            color: Colors.white,
+            icon: const Icon(Icons.play_arrow),
+            iconSize: 32.0,
+            onPressed: () async {
+              await controller.start();
+            },
+          );
+        }
+
+        return IconButton(
+          color: Colors.white,
+          icon: const Icon(Icons.stop),
+          iconSize: 32.0,
+          onPressed: () async {
+            await controller.stop();
+          },
+        );
+      },
+    );
+  }
+}
+
+class SwitchCameraButton extends StatelessWidget {
+  const SwitchCameraButton({required this.controller, super.key});
+
+  final MobileScannerController controller;
+
+  @override
+  Widget build(BuildContext context) {
+    return ValueListenableBuilder(
+      valueListenable: controller,
+      builder: (context, state, child) {
+        if (!state.isInitialized || !state.isRunning) {
+          return const SizedBox.shrink();
+        }
+
+        final Widget icon;
+
+        switch (state.cameraDirection) {
+          case CameraFacing.front:
+            icon = const Icon(Icons.camera_front);
+            break;
+          case CameraFacing.back:
+            icon = const Icon(Icons.camera_rear);
+            break;
+        }
+
+        return IconButton(
+          iconSize: 32.0,
+          icon: icon,
+          onPressed: () async {
+            await controller.switchCamera();
+          },
+        );
+      },
+    );
+  }
+}
+
+class ToggleFlashlightButton extends StatelessWidget {
+  const ToggleFlashlightButton({required this.controller, super.key});
+
+  final MobileScannerController controller;
+
+  @override
+  Widget build(BuildContext context) {
+    return ValueListenableBuilder(
+      valueListenable: controller,
+      builder: (context, state, child) {
+        if (!state.isInitialized || !state.isRunning) {
+          return const SizedBox.shrink();
+        }
+
+        switch (state.torchState) {
+          case TorchState.off:
+            return IconButton(
+              color: Colors.white,
+              iconSize: 32.0,
+              icon: const Icon(Icons.flash_off),
+              onPressed: () async {
+                await controller.toggleTorch();
+              },
+            );
+          case TorchState.on:
+            return IconButton(
+              color: Colors.white,
+              iconSize: 32.0,
+              icon: const Icon(Icons.flash_on),
+              onPressed: () async {
+                await controller.toggleTorch();
+              },
+            );
+          case TorchState.unavailable:
+            return const Icon(
+              Icons.no_flash,
+              color: Colors.grey,
+            );
+        }
+      },
+    );
+  }
+}