Merge pull request #1086 from navaronbracke/fix_already_started_bug

fix: Ignore additional calls to start() when the controller is starting

 ## NEXT
 
+Improvements:
 * [MacOS] Added the corners and size information to barcode results.
 * [MacOS] Added support for `analyzeImage`.
 * [MacOS] Added a Privacy Manifest.
 * [web] Added the size information to barcode results.
 * Added support for barcode formats to image analysis.
+* Updated the scanner to report any scanning errors that were encountered during processing.
+* Introduced a new getter `hasCameraPermission` for the `MobileScannerState`.
+* Fixed a bug in the lifecycle handling sample. Now instead of checking `isInitialized`,
+the sample recommends using `hasCameraPermission`, which also guards against camera permission errors.
+
+Bugs fixed:
+* Fixed a bug that would cause the scanner to emit an error when it was already started. Now it ignores any calls to start while it is starting.
+* [MacOS] Fixed a bug that prevented the `anaylzeImage()` sample from working properly.
 
 ## 5.2.3
 

@@ -127,7 +127,7 @@ class MyState extends State<MyStatefulWidget> with WidgetsBindingObserver {
   void didChangeAppLifecycleState(AppLifecycleState state) {
     // If the controller is not ready, do not try to start or stop it.
     // Permission dialogs can trigger lifecycle changes before the controller is ready.
-    if (!controller.value.isInitialized) {
+    if (!controller.value.hasCameraPermission) {
       return;
     }
 

@@ -18,6 +18,12 @@ class BarcodeHandler(binaryMessenger: BinaryMessenger) : EventChannel.StreamHand
         eventChannel.setStreamHandler(this)
     }
 
+    fun publishError(errorCode: String, errorMessage: String, errorDetails: Any?) {
+        Handler(Looper.getMainLooper()).post {
+            eventSink?.error(errorCode, errorMessage, errorDetails)
+        }
+    }
+
     fun publishEvent(event: Map<String, Any>) {
         Handler(Looper.getMainLooper()).post {
             eventSink?.success(event)

@@ -10,6 +10,7 @@ import androidx.camera.core.ExperimentalGetImage
 import com.google.mlkit.vision.barcode.BarcodeScannerOptions
 import dev.steenbakker.mobile_scanner.objects.BarcodeFormats
 import dev.steenbakker.mobile_scanner.objects.DetectionSpeed
+import dev.steenbakker.mobile_scanner.objects.MobileScannerErrorCodes
 import io.flutter.plugin.common.BinaryMessenger
 import io.flutter.plugin.common.MethodCall
 import io.flutter.plugin.common.MethodChannel
@@ -28,7 +29,7 @@ class MobileScannerHandler(
 
     private val analyzeImageErrorCallback: AnalyzerErrorCallback = {
         Handler(Looper.getMainLooper()).post {
-            analyzerResult?.error("MobileScanner", it, null)
+            analyzerResult?.error(MobileScannerErrorCodes.BARCODE_ERROR, it, null)
             analyzerResult = null
         }
     }
@@ -65,10 +66,7 @@ class MobileScannerHandler(
     }
 
     private val errorCallback: MobileScannerErrorCallback = {error: String ->
-        barcodeHandler.publishEvent(mapOf(
-            "name" to "error",
-            "data" to error,
-        ))
+        barcodeHandler.publishError(MobileScannerErrorCodes.BARCODE_ERROR, error, null)
     }
 
     private var methodChannel: MethodChannel? = null
@@ -106,21 +104,21 @@ class MobileScannerHandler(
 
     @ExperimentalGetImage
     override fun onMethodCall(call: MethodCall, result: MethodChannel.Result) {
-        if (mobileScanner == null) {
-            result.error("MobileScanner", "Called ${call.method} before initializing.", null)
-            return
-        }
         when (call.method) {
             "state" -> result.success(permissions.hasCameraPermission(activity))
             "request" -> permissions.requestPermission(
                 activity,
                 addPermissionListener,
                 object: MobileScannerPermissions.ResultCallback {
-                    override fun onResult(errorCode: String?, errorDescription: String?) {
+                    override fun onResult(errorCode: String?) {
                         when(errorCode) {
                             null -> result.success(true)
-                            MobileScannerPermissions.CAMERA_ACCESS_DENIED -> result.success(false)
-                            else -> result.error(errorCode, errorDescription, null)
+                            MobileScannerErrorCodes.CAMERA_ACCESS_DENIED -> result.success(false)
+                            MobileScannerErrorCodes.CAMERA_PERMISSIONS_REQUEST_ONGOING -> result.error(
+                                MobileScannerErrorCodes.CAMERA_PERMISSIONS_REQUEST_ONGOING,
+                                MobileScannerErrorCodes.CAMERA_PERMISSIONS_REQUEST_ONGOING_MESSAGE, null)
+                            else -> result.error(
+                                MobileScannerErrorCodes.GENERIC_ERROR, MobileScannerErrorCodes.GENERIC_ERROR_MESSAGE, null)
                         }
                     }
                 })
@@ -185,29 +183,29 @@ class MobileScannerHandler(
                     when (it) {
                         is AlreadyStarted -> {
                             result.error(
-                                "MobileScanner",
-                                "Called start() while already started",
+                                MobileScannerErrorCodes.ALREADY_STARTED_ERROR,
+                                MobileScannerErrorCodes.ALREADY_STARTED_ERROR_MESSAGE,
                                 null
                             )
                         }
                         is CameraError -> {
                             result.error(
-                                "MobileScanner",
-                                "Error occurred when setting up camera!",
+                                MobileScannerErrorCodes.CAMERA_ERROR,
+                                MobileScannerErrorCodes.CAMERA_ERROR_MESSAGE,
                                 null
                             )
                         }
                         is NoCamera -> {
                             result.error(
-                                "MobileScanner",
-                                "No camera found or failed to open camera!",
+                                MobileScannerErrorCodes.NO_CAMERA_ERROR,
+                                MobileScannerErrorCodes.NO_CAMERA_ERROR_MESSAGE,
                                 null
                             )
                         }
                         else -> {
                             result.error(
-                                "MobileScanner",
-                                "Unknown error occurred.",
+                                MobileScannerErrorCodes.GENERIC_ERROR,
+                                MobileScannerErrorCodes.GENERIC_ERROR_MESSAGE,
                                 null
                             )
                         }
@@ -252,9 +250,11 @@ class MobileScannerHandler(
             mobileScanner!!.setScale(call.arguments as Double)
             result.success(null)
         } catch (e: ZoomWhenStopped) {
-            result.error("MobileScanner", "Called setScale() while stopped!", null)
+            result.error(
+                MobileScannerErrorCodes.SET_SCALE_WHEN_STOPPED_ERROR, MobileScannerErrorCodes.SET_SCALE_WHEN_STOPPED_ERROR_MESSAGE, null)
         } catch (e: ZoomNotInRange) {
-            result.error("MobileScanner", "Scale should be within 0 and 1", null)
+            result.error(
+                MobileScannerErrorCodes.GENERIC_ERROR, MobileScannerErrorCodes.INVALID_ZOOM_SCALE_ERROR_MESSAGE, null)
         }
     }
 
@@ -263,7 +263,8 @@ class MobileScannerHandler(
             mobileScanner!!.resetScale()
             result.success(null)
         } catch (e: ZoomWhenStopped) {
-            result.error("MobileScanner", "Called resetScale() while stopped!", null)
+            result.error(
+                MobileScannerErrorCodes.SET_SCALE_WHEN_STOPPED_ERROR, MobileScannerErrorCodes.SET_SCALE_WHEN_STOPPED_ERROR_MESSAGE, null)
         }
     }
 

@@ -5,6 +5,7 @@ import android.app.Activity
 import android.content.pm.PackageManager
 import androidx.core.app.ActivityCompat
 import androidx.core.content.ContextCompat
+import dev.steenbakker.mobile_scanner.objects.MobileScannerErrorCodes
 import io.flutter.plugin.common.PluginRegistry.RequestPermissionsResultListener
 
 /**
@@ -12,11 +13,6 @@ import io.flutter.plugin.common.PluginRegistry.RequestPermissionsResultListener
  */
 class MobileScannerPermissions {
     companion object {
-        const val CAMERA_ACCESS_DENIED = "CameraAccessDenied"
-        const val CAMERA_ACCESS_DENIED_MESSAGE = "Camera access permission was denied."
-        const val CAMERA_PERMISSIONS_REQUEST_ONGOING = "CameraPermissionsRequestOngoing"
-        const val CAMERA_PERMISSIONS_REQUEST_ONGOING_MESSAGE = "Another request is ongoing and multiple requests cannot be handled at once."
-
         /**
          * When the application's activity is [androidx.fragment.app.FragmentActivity], requestCode can only use the lower 16 bits.
          * @see androidx.fragment.app.FragmentActivity.validateRequestPermissionsRequestCode
@@ -25,7 +21,7 @@ class MobileScannerPermissions {
     }
 
     interface ResultCallback {
-        fun onResult(errorCode: String?, errorDescription: String?)
+        fun onResult(errorCode: String?)
     }
 
     private var listener: RequestPermissionsResultListener? = null
@@ -53,14 +49,13 @@ class MobileScannerPermissions {
                           addPermissionListener: (RequestPermissionsResultListener) -> Unit,
                           callback: ResultCallback) {
         if (ongoing) {
-            callback.onResult(
-                CAMERA_PERMISSIONS_REQUEST_ONGOING, CAMERA_PERMISSIONS_REQUEST_ONGOING_MESSAGE)
+            callback.onResult(MobileScannerErrorCodes.CAMERA_PERMISSIONS_REQUEST_ONGOING)
             return
         }
 
         if(hasCameraPermission(activity) == 1) {
             // Permissions already exist. Call the callback with success.
-            callback.onResult(null, null)
+            callback.onResult(null)
             return
         }
 
@@ -68,10 +63,10 @@ class MobileScannerPermissions {
             // Keep track of the listener, so that it can be unregistered later.
             listener = MobileScannerPermissionsListener(
                 object: ResultCallback {
-                    override fun onResult(errorCode: String?, errorDescription: String?) {
+                    override fun onResult(errorCode: String?) {
                         ongoing = false
                         listener = null
-                        callback.onResult(errorCode, errorDescription)
+                        callback.onResult(errorCode)
                     }
                 }
             )

 package dev.steenbakker.mobile_scanner
 
 import android.content.pm.PackageManager
+import dev.steenbakker.mobile_scanner.objects.MobileScannerErrorCodes
 import io.flutter.plugin.common.PluginRegistry
 
 /**
@@ -29,11 +30,9 @@ internal class MobileScannerPermissionsListener(
         // grantResults could be empty if the permissions request with the user is interrupted
         // https://developer.android.com/reference/android/app/Activity#onRequestPermissionsResult(int,%20java.lang.String[],%20int[])
         if (grantResults.isEmpty() || grantResults[0] != PackageManager.PERMISSION_GRANTED) {
-            resultCallback.onResult(
-                MobileScannerPermissions.CAMERA_ACCESS_DENIED,
-                MobileScannerPermissions.CAMERA_ACCESS_DENIED_MESSAGE)
+            resultCallback.onResult(MobileScannerErrorCodes.CAMERA_ACCESS_DENIED)
         } else {
-            resultCallback.onResult(null, null)
+            resultCallback.onResult(null)
         }
 
         return true

@@ -5,9 +5,11 @@
 *.swp
 .DS_Store
 .atom/
+.build/
 .buildlog/
 .history
 .svn/
+.swiftpm/
 migrate_working_dir/
 
 # IntelliJ related

@@ -488,14 +488,14 @@
 				CODE_SIGN_IDENTITY = "Apple Development";
 				CODE_SIGN_STYLE = Automatic;
 				CURRENT_PROJECT_VERSION = "$(FLUTTER_BUILD_NUMBER)";
-				DEVELOPMENT_TEAM = 75Y2P2WSQQ;
+				DEVELOPMENT_TEAM = "";
 				ENABLE_BITCODE = NO;
 				INFOPLIST_FILE = Runner/Info.plist;
 				LD_RUNPATH_SEARCH_PATHS = (
 					"$(inherited)",
 					"@executable_path/Frameworks",
 				);
-				PRODUCT_BUNDLE_IDENTIFIER = "com.example.mobile-scanner";
+				PRODUCT_BUNDLE_IDENTIFIER = "com.example.mobile-scanner-example";
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				PROVISIONING_PROFILE_SPECIFIER = "";
 				SWIFT_OBJC_BRIDGING_HEADER = "Runner/Runner-Bridging-Header.h";
@@ -670,14 +670,14 @@
 				CODE_SIGN_IDENTITY = "Apple Development";
 				CODE_SIGN_STYLE = Automatic;
 				CURRENT_PROJECT_VERSION = "$(FLUTTER_BUILD_NUMBER)";
-				DEVELOPMENT_TEAM = 75Y2P2WSQQ;
+				DEVELOPMENT_TEAM = "";
 				ENABLE_BITCODE = NO;
 				INFOPLIST_FILE = Runner/Info.plist;
 				LD_RUNPATH_SEARCH_PATHS = (
 					"$(inherited)",
 					"@executable_path/Frameworks",
 				);
-				PRODUCT_BUNDLE_IDENTIFIER = "com.example.mobile-scanner";
+				PRODUCT_BUNDLE_IDENTIFIER = "com.example.mobile-scanner-example";
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				PROVISIONING_PROFILE_SPECIFIER = "";
 				SWIFT_OBJC_BRIDGING_HEADER = "Runner/Runner-Bridging-Header.h";
@@ -696,14 +696,14 @@
 				CODE_SIGN_IDENTITY = "Apple Development";
 				CODE_SIGN_STYLE = Automatic;
 				CURRENT_PROJECT_VERSION = "$(FLUTTER_BUILD_NUMBER)";
-				DEVELOPMENT_TEAM = 75Y2P2WSQQ;
+				DEVELOPMENT_TEAM = "";
 				ENABLE_BITCODE = NO;
 				INFOPLIST_FILE = Runner/Info.plist;
 				LD_RUNPATH_SEARCH_PATHS = (
 					"$(inherited)",
 					"@executable_path/Frameworks",
 				);
-				PRODUCT_BUNDLE_IDENTIFIER = "com.example.mobile-scanner";
+				PRODUCT_BUNDLE_IDENTIFIER = "com.example.mobile-scanner-example";
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				PROVISIONING_PROFILE_SPECIFIER = "";
 				SWIFT_OBJC_BRIDGING_HEADER = "Runner/Runner-Bridging-Header.h";

@@ -22,7 +22,14 @@ class _BarcodeScannerAnalyzeImageState
       final XFile? file =
           await ImagePicker().pickImage(source: ImageSource.gallery);
 
-      if (!mounted || file == null) {
+      if (!mounted) {
+        return;
+      }
+
+      if (file == null) {
+        setState(() {
+          _barcodeCapture = null;
+        });
         return;
       }
 
@@ -43,7 +50,7 @@ class _BarcodeScannerAnalyzeImageState
 
     if (_barcodeCapture != null) {
       label = Text(
-        _barcodeCapture?.barcodes.firstOrNull?.displayValue ??
+        _barcodeCapture?.barcodes.firstOrNull?.rawValue ??
             'No barcode detected',
       );
     }

@@ -6,4 +6,8 @@ class AppDelegate: FlutterAppDelegate {
   override func applicationShouldTerminateAfterLastWindowClosed(_ sender: NSApplication) -> Bool {
     return true
   }
+
+  override func applicationSupportsSecureRestorableState(_ app: NSApplication) -> Bool {
+    return true
+  }
 }

@@ -10,5 +10,7 @@
 	<true/>
 	<key>com.apple.security.network.server</key>
 	<true/>
+  	<key>com.apple.security.files.user-selected.read-only</key>
+  	<true/>	
 </dict>
 </plist>

@@ -21,7 +21,7 @@
   <meta name="description" content="Demonstrates how to use the mobile_scanner plugin.">
 
   <!-- iOS meta tags & icons -->
-  <meta name="apple-mobile-web-app-capable" content="yes">
+  <meta name="mobile-web-app-capable" content="yes">
   <meta name="apple-mobile-web-app-status-bar-style" content="black">
   <meta name="apple-mobile-web-app-title" content="mobile_scanner_example">
   <link rel="apple-touch-icon" href="icons/Icon-192.png">

@@ -19,6 +19,12 @@ public class BarcodeHandler: NSObject, FlutterStreamHandler {
         eventChannel.setStreamHandler(self)
     }
     
+    func publishError(_ error: FlutterError) {
+        DispatchQueue.main.async {
+            self.eventSink?(error)
+        }
+    }
+    
     func publishEvent(_ event: [String: Any?]) {
         DispatchQueue.main.async {
             self.eventSink?(event)

@@ -42,7 +42,10 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin {
     init(barcodeHandler: BarcodeHandler, registry: FlutterTextureRegistry) {
         self.mobileScanner = MobileScanner(registry: registry, mobileScannerCallback: { barcodes, error, image in
             if error != nil {
-                barcodeHandler.publishEvent(["name": "error", "data": error!.localizedDescription])
+                barcodeHandler.publishError(
+                    FlutterError(code: MobileScannerErrorCodes.BARCODE_ERROR,
+                                 message: error?.localizedDescription,
+                                 details: nil))
                 return
             }
             
@@ -150,20 +153,20 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin {
                 }
             }
         } catch MobileScannerError.alreadyStarted {
-            result(FlutterError(code: "MobileScanner",
-                                message: "Called start() while already started!",
+            result(FlutterError(code: MobileScannerErrorCodes.ALREADY_STARTED_ERROR,
+                                message: MobileScannerErrorCodes.ALREADY_STARTED_ERROR_MESSAGE,
                                 details: nil))
         } catch MobileScannerError.noCamera {
-            result(FlutterError(code: "MobileScanner",
-                                message: "No camera found or failed to open camera!",
+            result(FlutterError(code: MobileScannerErrorCodes.NO_CAMERA_ERROR,
+                                message: MobileScannerErrorCodes.NO_CAMERA_ERROR_MESSAGE,
                                 details: nil))
         } catch MobileScannerError.cameraError(let error) {
-            result(FlutterError(code: "MobileScanner",
-                                message: "Error occured when setting up camera!",
-                                details: error))
+            result(FlutterError(code: MobileScannerErrorCodes.CAMERA_ERROR,
+                                message: error.localizedDescription,
+                                details: nil))
         } catch {
-            result(FlutterError(code: "MobileScanner",
-                                message: "Unknown error occured.",
+            result(FlutterError(code: MobileScannerErrorCodes.GENERIC_ERROR,
+                                message: MobileScannerErrorCodes.GENERIC_ERROR_MESSAGE,
                                 details: nil))
         }
     }
@@ -186,25 +189,25 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin {
     private func setScale(_ call: FlutterMethodCall, _ result: @escaping FlutterResult) {
         let scale = call.arguments as? CGFloat
         if (scale == nil) {
-            result(FlutterError(code: "MobileScanner",
-                                message: "You must provide a scale when calling setScale!",
-                                details: nil))
+            result(FlutterError(code: MobileScannerErrorCodes.GENERIC_ERROR,
+                                message: MobileScannerErrorCodes.INVALID_ZOOM_SCALE_ERROR_MESSAGE,
+                                details: "The invalid zoom scale was nil."))
             return
         }
         do {
             try mobileScanner.setScale(scale!)
             result(nil)
         } catch MobileScannerError.zoomWhenStopped {
-            result(FlutterError(code: "MobileScanner",
-                                message: "Called setScale() while stopped!",
+            result(FlutterError(code: MobileScannerErrorCodes.SET_SCALE_WHEN_STOPPED_ERROR,
+                                message: MobileScannerErrorCodes.SET_SCALE_WHEN_STOPPED_ERROR_MESSAGE,
                                 details: nil))
         } catch MobileScannerError.zoomError(let error) {
-            result(FlutterError(code: "MobileScanner",
-                                message: "Error while zooming.",
-                                details: error))
+            result(FlutterError(code: MobileScannerErrorCodes.GENERIC_ERROR,
+                                message: error.localizedDescription,
+                                details: nil))
         } catch {
-            result(FlutterError(code: "MobileScanner",
-                                message: "Error while zooming.",
+            result(FlutterError(code: MobileScannerErrorCodes.GENERIC_ERROR,
+                                message: MobileScannerErrorCodes.GENERIC_ERROR_MESSAGE,
                                 details: nil))
         }
     }
@@ -215,16 +218,16 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin {
             try mobileScanner.resetScale()
             result(nil)
         } catch MobileScannerError.zoomWhenStopped {
-            result(FlutterError(code: "MobileScanner",
-                                message: "Called resetScale() while stopped!",
+            result(FlutterError(code: MobileScannerErrorCodes.SET_SCALE_WHEN_STOPPED_ERROR,
+                                message: MobileScannerErrorCodes.SET_SCALE_WHEN_STOPPED_ERROR_MESSAGE,
                                 details: nil))
         } catch MobileScannerError.zoomError(let error) {
-            result(FlutterError(code: "MobileScanner",
-                                message: "Error while zooming.",
-                                details: error))
+            result(FlutterError(code: MobileScannerErrorCodes.GENERIC_ERROR,
+                                message: error.localizedDescription,
+                                details: nil))
         } catch {
-            result(FlutterError(code: "MobileScanner",
-                                message: "Error while zooming.",
+            result(FlutterError(code: MobileScannerErrorCodes.GENERIC_ERROR,
+                                message: MobileScannerErrorCodes.GENERIC_ERROR_MESSAGE,
                                 details: nil))
         }
     }
@@ -266,7 +269,7 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin {
                                    barcodeScannerOptions: scannerOptions, callback: { barcodes, error in
             if error != nil {
                 DispatchQueue.main.async {
-                    result(FlutterError(code: "MobileScanner",
+                    result(FlutterError(code: MobileScannerErrorCodes.BARCODE_ERROR,
                                         message: error?.localizedDescription,
                                         details: nil))
                 }

@@ -11,8 +11,7 @@ export 'src/enums/phone_type.dart';
 export 'src/enums/torch_state.dart';
 export 'src/mobile_scanner.dart';
 export 'src/mobile_scanner_controller.dart';
-export 'src/mobile_scanner_exception.dart'
-    hide PermissionRequestPendingException;
+export 'src/mobile_scanner_exception.dart';
 export 'src/mobile_scanner_platform_interface.dart';
 export 'src/objects/address.dart';
 export 'src/objects/barcode.dart';

@@ -16,6 +16,14 @@ import 'package:mobile_scanner/src/objects/start_options.dart';
 
 /// An implementation of [MobileScannerPlatform] that uses method channels.
 class MethodChannelMobileScanner extends MobileScannerPlatform {
+  /// The name of the barcode event that is sent when a barcode is scanned.
+  @visibleForTesting
+  static const String kBarcodeEventName = 'barcode';
+
+  /// The name of the error event that is sent when a barcode scan error occurs.
+  @visibleForTesting
+  static const String kBarcodeErrorEventName = 'MOBILE_SCANNER_BARCODE_ERROR';
+
   /// The method channel used to interact with the native platform.
   @visibleForTesting
   final methodChannel = const MethodChannel(
@@ -79,6 +87,19 @@ class MethodChannelMobileScanner extends MobileScannerPlatform {
     );
   }
 
+  /// Parse a [MobileScannerBarcodeException] from the given [error] and [stackTrace], and throw it.
+  ///
+  /// If the error is not a [PlatformException],
+  /// with [kBarcodeErrorEventName] as [PlatformException.code], the error is rethrown as-is.
+  Never _parseBarcodeError(Object error, StackTrace stackTrace) {
+    if (error case PlatformException(:final String code, :final String? message)
+        when code == kBarcodeErrorEventName) {
+      throw MobileScannerBarcodeException(message);
+    }
+
+    Error.throwWithStackTrace(error, stackTrace);
+  }
+
   /// Request permission to access the camera.
   ///
   /// Throws a [MobileScannerException] if the permission is not granted.
@@ -121,9 +142,12 @@ class MethodChannelMobileScanner extends MobileScannerPlatform {
 
   @override
   Stream<BarcodeCapture?> get barcodesStream {
+    // Handle incoming barcode events.
+    // The error events are transformed to `MobileScannerBarcodeException` where possible.
     return eventsStream
-        .where((event) => event['name'] == 'barcode')
-        .map((event) => _parseBarcode(event));
+        .where((e) => e['name'] == kBarcodeEventName)
+        .map((event) => _parseBarcode(event))
+        .handleError(_parseBarcodeError);
   }
 
   @override
@@ -145,6 +169,7 @@ class MethodChannelMobileScanner extends MobileScannerPlatform {
     String path, {
     List<BarcodeFormat> formats = const <BarcodeFormat>[],
   }) async {
+    try {
       final Map<Object?, Object?>? result =
           await methodChannel.invokeMapMethod<Object?, Object?>(
         'analyzeImage',
@@ -160,6 +185,14 @@ class MethodChannelMobileScanner extends MobileScannerPlatform {
       );
 
       return _parseBarcode(result);
+    } on PlatformException catch (error) {
+      // Handle any errors from analyze image requests.
+      if (error.code == kBarcodeErrorEventName) {
+        throw MobileScannerBarcodeException(error.message);
+      }
+
+      return null;
+    }
   }
 
   @override

@@ -35,6 +35,12 @@ class MobileScanner extends StatefulWidget {
 
   /// The function that signals when new codes were detected by the [controller].
   /// If null, use the controller.barcodes stream directly to capture barcodes.
+  ///
+  /// This method does not receive any [MobileScannerBarcodeException]s
+  /// that are emitted by the scanner.
+  ///
+  /// To handle both [BarcodeCapture]s and [MobileScannerBarcodeException]s,
+  /// use the [MobileScannerController.barcodes] stream directly.
   final void Function(BarcodeCapture barcodes)? onDetect;
 
   /// The error builder for the camera preview.

@@ -102,6 +102,9 @@ class MobileScannerController extends ValueNotifier<MobileScannerState> {
       StreamController.broadcast();
 
   /// Get the stream of scanned barcodes.
+  ///
+  /// If an error occurred during the detection of a barcode,
+  /// a [MobileScannerBarcodeException] error is emitted to the stream.
   Stream<BarcodeCapture> get barcodes => _barcodesController.stream;
 
   StreamSubscription<BarcodeCapture?>? _barcodesSubscription;
@@ -121,14 +124,25 @@ class MobileScannerController extends ValueNotifier<MobileScannerState> {
   }
 
   void _setupListeners() {
-    _barcodesSubscription = MobileScannerPlatform.instance.barcodesStream
-        .listen((BarcodeCapture? barcode) {
+    _barcodesSubscription =
+        MobileScannerPlatform.instance.barcodesStream.listen(
+      (BarcodeCapture? barcode) {
         if (_barcodesController.isClosed || barcode == null) {
           return;
         }
 
         _barcodesController.add(barcode);
-    });
+      },
+      onError: (Object error) {
+        if (_barcodesController.isClosed) {
+          return;
+        }
+
+        _barcodesController.addError(error);
+      },
+      // Errors are handled gracefully by forwarding them.
+      cancelOnError: false,
+    );
 
     _torchStateSubscription = MobileScannerPlatform.instance.torchStateStream
         .listen((TorchState torchState) {
@@ -177,6 +191,9 @@ class MobileScannerController extends ValueNotifier<MobileScannerState> {
   /// This is only supported on Android, iOS and MacOS.
   ///
   /// Returns the [BarcodeCapture] that was found in the image.
+  ///
+  /// If an error occurred during the analysis of the image,
+  /// a [MobileScannerBarcodeException] error is thrown.
   Future<BarcodeCapture?> analyzeImage(String path) {
     return MobileScannerPlatform.instance.analyzeImage(path);
   }
@@ -246,13 +263,6 @@ class MobileScannerController extends ValueNotifier<MobileScannerState> {
       );
     }
 
-    // Permission was denied, do nothing.
-    // When the controller is stopped,
-    // the error is reset so the permission can be requested again if possible.
-    if (value.error?.errorCode == MobileScannerErrorCode.permissionDenied) {
-      return;
-    }
-
     // Do nothing if the camera is already running.
     if (value.isRunning) {
       return;
@@ -292,6 +302,13 @@ class MobileScannerController extends ValueNotifier<MobileScannerState> {
         );
       }
     } on MobileScannerException catch (error) {
+      // If the controller is already initialized, ignore the error.
+      // Starting the controller while it is already started, or in the process of starting, is redundant.
+      if (error.errorCode ==
+          MobileScannerErrorCode.controllerAlreadyInitialized) {
+        return;
+      }
+
       // The initialization finished with an error.
       // To avoid stale values, reset the output size,
       // torch state and zoom scale to the defaults.
@@ -306,8 +323,6 @@ class MobileScannerController extends ValueNotifier<MobileScannerState> {
           zoomScale: 1.0,
         );
       }
-    } on PermissionRequestPendingException catch (_) {
-      // If a permission request was already pending, do nothing.
     }
   }
 

@@ -40,13 +40,6 @@ class MobileScannerErrorDetails {
   final String? message;
 }
 
-/// This class represents an exception that is thrown
-/// when the scanner was (re)started while a permission request was pending.
-///
-/// This exception type is only used internally,
-/// and is not part of the public API.
-class PermissionRequestPendingException implements Exception {}
-
 /// This class represents an exception thrown by the [MobileScannerController]
 /// when a barcode scanning error occurs when processing an input frame.
 class MobileScannerBarcodeException implements Exception {

@@ -39,12 +39,6 @@ class MobileScannerWeb extends MobileScannerPlatform {
   /// The container div element for the camera view.
   late HTMLDivElement _divElement;
 
-  /// The flag that keeps track of whether a permission request is in progress.
-  ///
-  /// On the web, a permission request triggers a dialog, that in turn triggers a lifecycle change.
-  /// While the permission request is in progress, any attempts at (re)starting the camera should be ignored.
-  bool _permissionRequestInProgress = false;
-
   /// The stream controller for the media track settings stream.
   ///
   /// Currently, only the facing mode setting can be supported,
@@ -199,17 +193,12 @@ class MobileScannerWeb extends MobileScannerPlatform {
     }
 
     try {
-      _permissionRequestInProgress = true;
-
       // Retrieving the media devices requests the camera permission.
       final MediaStream videoStream =
           await window.navigator.mediaDevices.getUserMedia(constraints).toDart;
 
-      _permissionRequestInProgress = false;
-
       return videoStream;
     } on DOMException catch (error, stackTrace) {
-      _permissionRequestInProgress = false;
       final String errorMessage = error.toString();
 
       MobileScannerErrorCode errorCode = MobileScannerErrorCode.genericError;
@@ -272,11 +261,13 @@ class MobileScannerWeb extends MobileScannerPlatform {
 
   @override
   Future<MobileScannerViewAttributes> start(StartOptions startOptions) async {
-    // If the permission request has not yet completed,
-    // the camera view is not ready yet.
-    // Prevent the permission popup from triggering a restart of the scanner.
-    if (_permissionRequestInProgress) {
-      throw PermissionRequestPendingException();
+    if (_barcodeReader != null) {
+      throw const MobileScannerException(
+        errorCode: MobileScannerErrorCode.controllerAlreadyInitialized,
+        errorDetails: MobileScannerErrorDetails(
+          message: 'The scanner was already started.',
+        ),
+      );
     }
 
     _barcodeReader = ZXingBarcodeReader();
@@ -285,16 +276,6 @@ class MobileScannerWeb extends MobileScannerPlatform {
       alternateScriptUrl: _alternateScriptUrl,
     );
 
-    if (_barcodeReader?.isScanning ?? false) {
-      throw const MobileScannerException(
-        errorCode: MobileScannerErrorCode.controllerAlreadyInitialized,
-        errorDetails: MobileScannerErrorDetails(
-          message:
-              'The scanner was already started. Call stop() before calling start() again.',
-        ),
-      );
-    }
-
     // Request camera permissions and prepare the video stream.
     final MediaStream videoStream = await _prepareVideoStream(
       startOptions.cameraDirection,
@@ -341,6 +322,15 @@ class MobileScannerWeb extends MobileScannerPlatform {
 
           _barcodesController.add(barcode);
         },
+        onError: (Object error) {
+          if (_barcodesController.isClosed) {
+            return;
+          }
+
+          _barcodesController.addError(error);
+        },
+        // Errors are handled gracefully by forwarding them.
+        cancelOnError: false,
       );
 
       final bool hasTorch = await _barcodeReader?.hasTorch() ?? false;

@@ -2,7 +2,9 @@ import 'dart:async';
 import 'dart:js_interop';
 import 'dart:ui';
 
+import 'package:flutter/foundation.dart';
 import 'package:mobile_scanner/src/enums/barcode_format.dart';
+import 'package:mobile_scanner/src/mobile_scanner_exception.dart';
 import 'package:mobile_scanner/src/objects/barcode_capture.dart';
 import 'package:mobile_scanner/src/objects/start_options.dart';
 import 'package:mobile_scanner/src/web/barcode_reader.dart';
@@ -10,12 +12,18 @@ import 'package:mobile_scanner/src/web/javascript_map.dart';
 import 'package:mobile_scanner/src/web/media_track_constraints_delegate.dart';
 import 'package:mobile_scanner/src/web/zxing/result.dart';
 import 'package:mobile_scanner/src/web/zxing/zxing_browser_multi_format_reader.dart';
+import 'package:mobile_scanner/src/web/zxing/zxing_exception.dart';
 import 'package:web/web.dart' as web;
 
 /// A barcode reader implementation that uses the ZXing library.
 final class ZXingBarcodeReader extends BarcodeReader {
   ZXingBarcodeReader();
 
+  /// ZXing reports an error with this message if the code could not be detected.
+  @visibleForTesting
+  static const String kNoCodeDetectedErrorMessage =
+      'No MultiFormat Readers were able to detect the code.';
+
   /// The listener for media track settings changes.
   void Function(web.MediaTrackSettings)? _onMediaTrackSettingsChanged;
 
@@ -98,16 +106,24 @@ final class ZXingBarcodeReader extends BarcodeReader {
       _reader?.decodeContinuously.callAsFunction(
         _reader,
         _reader?.videoElement,
-        (Result? result, JSAny? error) {
-          if (controller.isClosed || result == null) {
+        (Result? result, ZXingException? error) {
+          if (controller.isClosed) {
             return;
           }
 
+          // Skip the event if no code was detected.
+          if (error != null && error.message != kNoCodeDetectedErrorMessage) {
+            controller.addError(MobileScannerBarcodeException(error.message));
+            return;
+          }
+
+          if (result != null) {
             controller.add(
               BarcodeCapture(
                 barcodes: [result.toBarcode],
               ),
             );
+          }
         }.toJS,
       );
     };

+import 'dart:js_interop';
+
+/// The JS static interop class for the Result class in the ZXing library.
+///
+/// See also: https://github.com/zxing-js/library/blob/master/src/core/Exception.ts
+@JS('ZXing.Exception')
+extension type ZXingException._(JSObject _) implements JSObject {
+  /// The error message of the exception, if any.
+  external String? get message;
+}

@@ -131,7 +131,9 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler,
                         
                         if error != nil {
                             DispatchQueue.main.async {
-                                self?.sink?(FlutterError(code: "MobileScanner", message: error?.localizedDescription, details: nil))
+                                self?.sink?(FlutterError(
+                                    code: MobileScannerErrorCodes.BARCODE_ERROR,
+                                    message: error?.localizedDescription, details: nil))
                             }
                             return
                         }
@@ -180,9 +182,11 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler,
                     }
 
                     try imageRequestHandler.perform([barcodeRequest])
-                } catch let e {
+                } catch let error {
                     DispatchQueue.main.async {
-                        self?.sink?(FlutterError(code: "MobileScanner", message: e.localizedDescription, details: nil))
+                        self?.sink?(FlutterError(
+                            code: MobileScannerErrorCodes.BARCODE_ERROR,
+                            message: error.localizedDescription, details: nil))
                     }
                 }
             }
@@ -262,8 +266,8 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler,
 
     func start(_ call: FlutterMethodCall, _ result: @escaping FlutterResult) {
         if (device != nil || captureSession != nil) {
-            result(FlutterError(code: "MobileScanner",
-                                message: "Called start() while already started!",
+            result(FlutterError(code: MobileScannerErrorCodes.ALREADY_STARTED_ERROR,
+                                message: MobileScannerErrorCodes.ALREADY_STARTED_ERROR_MESSAGE,
                                 details: nil))
             return
         }
@@ -294,8 +298,8 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler,
         }
         
         if (device == nil) {
-            result(FlutterError(code: "MobileScanner",
-                                message: "No camera found or failed to open camera!",
+            result(FlutterError(code: MobileScannerErrorCodes.NO_CAMERA_ERROR,
+                                message: MobileScannerErrorCodes.NO_CAMERA_ERROR_MESSAGE,
                                 details: nil))
             return
         }
@@ -313,7 +317,9 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler,
             let input = try AVCaptureDeviceInput(device: device)
             captureSession!.addInput(input)
         } catch {
-            result(FlutterError(code: "MobileScanner", message: error.localizedDescription, details: nil))
+            result(FlutterError(
+                code: MobileScannerErrorCodes.CAMERA_ERROR,
+                message: error.localizedDescription, details: nil))
             return
         }
         captureSession!.sessionPreset = AVCaptureSession.Preset.photo
@@ -476,8 +482,9 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler,
                     
                 if error != nil {
                     DispatchQueue.main.async {
-                        // TODO: fix error code
-                        result(FlutterError(code: "MobileScanner", message: error?.localizedDescription, details: nil))
+                        result(FlutterError(
+                            code: MobileScannerErrorCodes.BARCODE_ERROR,
+                            message: error?.localizedDescription, details: nil))
                     }
                     return
                 }
@@ -502,10 +509,11 @@ public class MobileScannerPlugin: NSObject, FlutterPlugin, FlutterStreamHandler,
             }
             
             try imageRequestHandler.perform([barcodeRequest])
-        } catch let e {
-            // TODO: fix error code
+        } catch let error {
             DispatchQueue.main.async {
-                result(FlutterError(code: "MobileScanner", message: e.localizedDescription, details: nil))
+                result(FlutterError(
+                    code: MobileScannerErrorCodes.BARCODE_ERROR,
+                    message: error.localizedDescription, details: nil))
             }
         }
     }