imp: improve error handling, add scanner_error_widget.dart to lib and show error…

… messages when kdebugmode is true

@@ -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 +19,11 @@ class ScannerErrorWidget extends StatelessWidget {
               child: Icon(Icons.error, color: Colors.white),
             ),
             Text(
-              errorMessage,
+              error.errorCode.message,
               style: const TextStyle(color: Colors.white),
             ),
-            Text(
-              error.errorDetails?.message ?? '',
+            if (error.errorDetails != null) Text(
+              error.errorDetails!.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,
         ),
       );
     }

@@ -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.
@@ -199,6 +200,8 @@ class _MobileScannerState extends State<MobileScanner>
     return ValueListenableBuilder<MobileScannerState>(
       valueListenable: controller,
       builder: (BuildContext context, MobileScannerState value, Widget? child) {
+
+        // If the controller is still initializing, show a black screen, or user provided placeholder
         if (!value.isInitialized) {
           const Widget defaultPlaceholder = ColoredBox(color: Colors.black);
 
@@ -207,12 +210,9 @@ class _MobileScannerState extends State<MobileScanner>
         }
 
         final MobileScannerException? error = value.error;
-
+        // If the controller encountered, show an error screen, or user provided placeholder
         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;

@@ -164,20 +164,20 @@ 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.',
+          MobileScannerErrorCode.controllerDisposed.message,
         ),
       );
     }
@@ -284,11 +284,10 @@ 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,
         ),
       );
     }

+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 != null) Text(
+              error.errorDetails!.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,
         ),
       );
     }