Merge pull request #1392 from juliansteenbakker/hotfix/usage-after-dispose

fix: black screen after multiple initialization

@@ -59,6 +59,7 @@
       ignoresPersistentStateOnLaunch = "NO"
       debugDocumentVersioning = "YES"
       debugServiceExtension = "internal"
+      enableGPUValidationMode = "1"
       allowLocationSimulation = "YES">
       <BuildableProductRunnable
          runnableDebuggingMode = "0">

@@ -8,19 +8,6 @@ class ScannerErrorWidget extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    String errorMessage;
-
-    switch (error.errorCode) {
-      case MobileScannerErrorCode.controllerUninitialized:
-        errorMessage = 'Controller not ready.';
-      case MobileScannerErrorCode.permissionDenied:
-        errorMessage = 'Permission denied';
-      case MobileScannerErrorCode.unsupported:
-        errorMessage = 'Scanning is unsupported on this device';
-      default:
-        errorMessage = 'Generic Error';
-    }
-
     return ColoredBox(
       color: Colors.black,
       child: Center(
@@ -32,11 +19,12 @@ class ScannerErrorWidget extends StatelessWidget {
               child: Icon(Icons.error, color: Colors.white),
             ),
             Text(
-              errorMessage,
+              error.errorCode.message,
               style: const TextStyle(color: Colors.white),
             ),
+            if (error.errorDetails?.message case final String message)
               Text(
-              error.errorDetails?.message ?? '',
+                message,
                 style: const TextStyle(color: Colors.white),
               ),
           ],

@@ -27,6 +27,23 @@ enum MobileScannerErrorCode {
   /// Scanning is unsupported on the current device.
   unsupported;
 
+  String get message {
+    switch (this) {
+      case MobileScannerErrorCode.controllerUninitialized:
+        return 'The MobileScannerController has not been initialized. Call start() before using it.';
+      case MobileScannerErrorCode.permissionDenied:
+        return 'Camera permission denied.';
+      case MobileScannerErrorCode.unsupported:
+        return 'Scanning is not supported on this device.';
+      case MobileScannerErrorCode.controllerAlreadyInitialized:
+        return 'The MobileScannerController is already running. Stop it before starting again.';
+      case MobileScannerErrorCode.controllerDisposed:
+        return 'The MobileScannerController was used after it was disposed.';
+      case MobileScannerErrorCode.genericError:
+        return 'An unexpected error occurred.';
+    }
+  }
+
   /// Convert the given [PlatformException.code] to a [MobileScannerErrorCode].
   factory MobileScannerErrorCode.fromPlatformException(
     PlatformException exception,

@@ -80,10 +80,10 @@ class MethodChannelMobileScanner extends MobileScannerPlatform {
       );
     }
 
-    throw const MobileScannerException(
-      errorCode: MobileScannerErrorCode.genericError,
+    throw MobileScannerException(
+      errorCode: MobileScannerErrorCode.unsupported,
       errorDetails: MobileScannerErrorDetails(
-        message: 'Only Android, iOS and macOS are supported.',
+        message: MobileScannerErrorCode.unsupported.message,
       ),
     );
   }
@@ -218,10 +218,10 @@ class MethodChannelMobileScanner extends MobileScannerPlatform {
   @override
   Future<MobileScannerViewAttributes> start(StartOptions startOptions) async {
     if (!_pausing && _textureId != null) {
-      throw const MobileScannerException(
+      throw MobileScannerException(
         errorCode: MobileScannerErrorCode.controllerAlreadyInitialized,
         errorDetails: MobileScannerErrorDetails(
-          message: 'The scanner was already started.',
+          message: MobileScannerErrorCode.controllerAlreadyInitialized.message,
         ),
       );
     }
@@ -339,6 +339,7 @@ class MethodChannelMobileScanner extends MobileScannerPlatform {
 
   @override
   Future<void> dispose() async {
+    await updateScanWindow(null);
     await stop();
   }
 }

@@ -6,6 +6,7 @@ import 'package:mobile_scanner/src/mobile_scanner_exception.dart';
 import 'package:mobile_scanner/src/mobile_scanner_platform_interface.dart';
 import 'package:mobile_scanner/src/objects/barcode_capture.dart';
 import 'package:mobile_scanner/src/objects/mobile_scanner_state.dart';
+import 'package:mobile_scanner/src/objects/scanner_error_widget.dart';
 import 'package:mobile_scanner/src/scan_window_calculation.dart';
 
 /// The function signature for the error builder.
@@ -134,7 +135,7 @@ class MobileScanner extends StatefulWidget {
 
 class _MobileScannerState extends State<MobileScanner>
     with WidgetsBindingObserver {
-  late final controller = widget.controller ?? MobileScannerController();
+  late final MobileScannerController controller;
 
   /// The current scan window.
   Rect? scanWindow;
@@ -207,12 +208,8 @@ class _MobileScannerState extends State<MobileScanner>
         }
 
         final MobileScannerException? error = value.error;
-
         if (error != null) {
-          const Widget defaultError = ColoredBox(
-            color: Colors.black,
-            child: Center(child: Icon(Icons.error, color: Colors.white)),
-          );
+          final Widget defaultError = ScannerErrorWidget(error: error);
 
           return widget.errorBuilder?.call(context, error, child) ??
               defaultError;
@@ -259,9 +256,22 @@ class _MobileScannerState extends State<MobileScanner>
 
   StreamSubscription? _subscription;
 
-  @override
-  void initState() {
-    if (widget.onDetect != null) {
+  Future<void> initMobileScanner() async {
+    // TODO: This will be fixed in another PR
+    // If debug mode is enabled, stop the controller first before starting it.
+    // If a hot-restart is initiated, the controller won't be stopped, and because
+    // there is no way of knowing if a hot-restart has happened, we must assume
+    // every start is a hot-restart.
+    // if (kDebugMode) {
+    //   try {
+    //     await controller.stop();
+    //   } catch (e) {
+    //     // Don't do anything if the controller is already stopped.
+    //     debugPrint('$e');
+    //   }
+    // }
+
+    if (widget.controller == null) {
       WidgetsBinding.instance.addObserver(this);
       _subscription = controller.barcodes.listen(
         widget.onDetect,
@@ -270,36 +280,44 @@ class _MobileScannerState extends State<MobileScanner>
       );
     }
     if (controller.autoStart) {
-      controller.start();
+      await controller.start();
     }
-    super.initState();
   }
 
-  @override
-  void dispose() {
-    super.dispose();
+  Future<void> disposeMobileScanner() async {
+    if (widget.controller == null) {
+      WidgetsBinding.instance.removeObserver(this);
+    }
 
-    if (_subscription != null) {
-      _subscription!.cancel();
+    await _subscription?.cancel();
     _subscription = null;
-    }
 
     if (controller.autoStart) {
-      controller.stop();
+      await controller.stop();
     }
-    // When this widget is unmounted, reset the scan window.
-    unawaited(controller.updateScanWindow(null));
 
     // Dispose default controller if not provided by user
     if (widget.controller == null) {
-      controller.dispose();
-      WidgetsBinding.instance.removeObserver(this);
+      await controller.dispose();
+    }
   }
+
+  @override
+  void initState() {
+    super.initState();
+    controller = widget.controller ?? MobileScannerController();
+    unawaited(initMobileScanner());
+  }
+
+  @override
+  void dispose() {
+    super.dispose();
+    unawaited(disposeMobileScanner());
   }
 
   @override
   void didChangeAppLifecycleState(AppLifecycleState state) {
-    if (widget.controller != null || !controller.value.hasCameraPermission) {
+    if (!controller.value.hasCameraPermission) {
       return;
     }
 
@@ -309,16 +327,8 @@ class _MobileScannerState extends State<MobileScanner>
       case AppLifecycleState.paused:
         return;
       case AppLifecycleState.resumed:
-        _subscription = controller.barcodes.listen(
-          widget.onDetect,
-          onError: widget.onDetectError,
-          cancelOnError: false,
-        );
-
         unawaited(controller.start());
       case AppLifecycleState.inactive:
-        unawaited(_subscription?.cancel());
-        _subscription = null;
         unawaited(controller.stop());
     }
   }

@@ -164,20 +164,19 @@ class MobileScannerController extends ValueNotifier<MobileScannerState> {
 
   void _throwIfNotInitialized() {
     if (!value.isInitialized) {
-      throw const MobileScannerException(
+      throw MobileScannerException(
         errorCode: MobileScannerErrorCode.controllerUninitialized,
         errorDetails: MobileScannerErrorDetails(
-          message: 'The MobileScannerController has not been initialized.',
+          message: MobileScannerErrorCode.controllerUninitialized.message,
         ),
       );
     }
 
     if (_isDisposed) {
-      throw const MobileScannerException(
+      throw MobileScannerException(
         errorCode: MobileScannerErrorCode.controllerDisposed,
         errorDetails: MobileScannerErrorDetails(
-          message:
-              'The MobileScannerController was used after it has been disposed.',
+          message: MobileScannerErrorCode.controllerDisposed.message,
         ),
       );
     }
@@ -284,11 +283,10 @@ class MobileScannerController extends ValueNotifier<MobileScannerState> {
   /// If the permission is denied on iOS, MacOS or Web, there is no way to request it again.
   Future<void> start({CameraFacing? cameraDirection}) async {
     if (_isDisposed) {
-      throw const MobileScannerException(
+      throw MobileScannerException(
         errorCode: MobileScannerErrorCode.controllerDisposed,
         errorDetails: MobileScannerErrorDetails(
-          message:
-              'The MobileScannerController was used after it has been disposed.',
+          message: MobileScannerErrorCode.controllerDisposed.message,
         ),
       );
     }
@@ -332,13 +330,6 @@ 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.

+import 'package:flutter/foundation.dart';
+import 'package:flutter/material.dart';
+import 'package:mobile_scanner/mobile_scanner.dart';
+
+class ScannerErrorWidget extends StatelessWidget {
+  const ScannerErrorWidget({super.key, required this.error});
+
+  final MobileScannerException error;
+
+  @override
+  Widget build(BuildContext context) {
+    return ColoredBox(
+      color: Colors.black,
+      child: Center(
+        child: Column(
+          mainAxisSize: MainAxisSize.min,
+          children: [
+            const Padding(
+              padding: EdgeInsets.only(bottom: 16),
+              child: Icon(Icons.error, color: Colors.white),
+            ),
+            if (kDebugMode) ...[
+              Text(
+                error.errorCode.message,
+                style: const TextStyle(color: Colors.white),
+              ),
+              if (error.errorDetails?.message case final String message)
+                Text(
+                  message,
+                  style: const TextStyle(color: Colors.white),
+                ),
+            ] else
+              Text(
+                MobileScannerErrorCode.genericError.message,
+                style: const TextStyle(color: Colors.white),
+              ),
+          ],
+        ),
+      ),
+    );
+  }
+}

@@ -273,10 +273,10 @@ class MobileScannerWeb extends MobileScannerPlatform {
         );
       }
 
-      throw const MobileScannerException(
+      throw MobileScannerException(
         errorCode: MobileScannerErrorCode.controllerAlreadyInitialized,
         errorDetails: MobileScannerErrorDetails(
-          message: 'The scanner was already started.',
+          message: MobileScannerErrorCode.controllerAlreadyInitialized.message,
         ),
       );
     }