fix: Camera activation after native view + double camera init on first start

packages/smooth_app/lib/pages/scan/lifecycle_manager.dart

@@ -1,8 +1,9 @@
+import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
 import 'package:visibility_detector/visibility_detector.dart';
 
-/// This Widgets tracks if the scanner is currently visible and if the app
-/// is currently open/idle/closed and controls the camera depending
+/// This Widgets tracks if the child is currently visible on screen and if the
+/// app gets minimized/resumed by the system
 class LifeCycleManager extends StatefulWidget {
   const LifeCycleManager({
     required this.onResume,
@@ -21,6 +22,19 @@ class LifeCycleManager extends StatefulWidget {
 
 class LifeCycleManagerState extends State<LifeCycleManager>
     with WidgetsBindingObserver {
+  double visibleFraction = 100.0;
+  AppLifecycleState appLifecycleState = AppLifecycleState.resumed;
+
+  void checkLifeCycle() {
+    if (appLifecycleState == AppLifecycleState.inactive ||
+        visibleFraction == 0.0) {
+      widget.onPause.call();
+    } else if (appLifecycleState == AppLifecycleState.resumed &&
+        visibleFraction > 0.0) {
+      widget.onResume.call();
+    }
+  }
+
   @override
   void initState() {
     super.initState();
@@ -40,23 +54,17 @@ class LifeCycleManagerState extends State<LifeCycleManager>
   // background or returns the app to the foreground.
   @override
   void didChangeAppLifecycleState(AppLifecycleState state) {
-    if (state == AppLifecycleState.inactive) {
-      widget.onPause.call();
-    } else if (state == AppLifecycleState.resumed) {
-      widget.onResume.call();
-    }
+    appLifecycleState = state;
+    checkLifeCycle();
   }
 
   @override
   Widget build(BuildContext context) {
     return VisibilityDetector(
       key: const ValueKey<String>('VisibilityDetector'),
       onVisibilityChanged: (VisibilityInfo info) {
-        if (info.visibleFraction == 0.0) {
-          widget.onPause.call();
-        } else {
-          widget.onResume.call();
-        }
+        visibleFraction = info.visibleFraction;
+        checkLifeCycle();
       },
       child: widget.child,
     );

packages/smooth_app/lib/pages/scan/ml_kit_scan_page.dart

@@ -110,31 +110,31 @@ class MLKitScannerPageState extends State<MLKitScannerPage> {
   }
 
   Future<void> _startLiveFeed() async {
+    if (_controller != null) {
+      return;
+    }
+
     stoppingCamera = false;
     final CameraDescription camera = cameras[_cameraIndex];
 
-    final CameraController cameraController = CameraController(
+    _controller = CameraController(
       camera,
       ResolutionPreset.high,
       enableAudio: false,
     );
-    cameraController.setFocusMode(FocusMode.auto);
-    cameraController.lockCaptureOrientation(DeviceOrientation.portraitUp);
+    _controller?.setFocusMode(FocusMode.auto);
+    _controller?.lockCaptureOrientation(DeviceOrientation.portraitUp);
 
-    _controller = cameraController;
+    _controller = _controller;
 
-    // If the controller is updated then update the UI.
-    cameraController.addListener(() {
+    try {
+      await _controller!.initialize();
       if (mounted) {
         setState(() {});
       }
-      if (cameraController.value.hasError) {
-        debugPrint(cameraController.value.errorDescription);
+      if (_controller!.value.hasError) {
+        debugPrint(_controller!.value.errorDescription);
       }
-    });
-
-    try {
-      await cameraController.initialize();
       _controller?.startImageStream(_processCameraImage);
     } on CameraException catch (e) {
       if (kDebugMode) {
@@ -154,6 +154,7 @@ class MLKitScannerPageState extends State<MLKitScannerPage> {
       setState(() {});
     }
     await _controller?.dispose();
+    _controller = null;
   }
 
   //Convert the [CameraImage] to a [InputImage]