bug: fix black screen on pageview and scanwindow not being reverted.

@@ -19,23 +19,6 @@ import dev.steenbakker.mobile_scanner.objects.MobileScannerStartParameters
 import io.flutter.view.TextureRegistry
 import kotlin.math.roundToInt
 
-
-typealias MobileScannerCallback = (barcodes: List<Map<String, Any?>>, image: ByteArray?, width: Int?, height: Int?) -> Unit
-typealias AnalyzerCallback = (barcodes: List<Map<String, Any?>>?) -> Unit
-typealias MobileScannerErrorCallback = (error: String) -> Unit
-typealias TorchStateCallback = (state: Int) -> Unit
-typealias MobileScannerStartedCallback = (parameters: MobileScannerStartParameters) -> Unit
-
-
-class NoCamera : Exception()
-class AlreadyStarted : Exception()
-class AlreadyStopped : Exception()
-class TorchError : Exception()
-class CameraError : Exception()
-class TorchWhenStopped : Exception()
-class ZoomWhenStopped : Exception()
-class ZoomNotInRange : Exception()
-
 class MobileScanner(
     private val activity: Activity,
     private val textureRegistry: TextureRegistry,
@@ -43,22 +26,21 @@ class MobileScanner(
     private val mobileScannerErrorCallback: MobileScannerErrorCallback
 ) {
 
+    /// Internal variables
     private var cameraProvider: ProcessCameraProvider? = null
     private var camera: Camera? = null
     private var preview: Preview? = null
     private var textureEntry: TextureRegistry.SurfaceTextureEntry? = null
-    var scanWindow: List<Float>? = null
-
-    private var detectionSpeed: DetectionSpeed = DetectionSpeed.NO_DUPLICATES
-    private var detectionTimeout: Long = 250
+    private var scanner = BarcodeScanning.getClient()
     private var lastScanned: List<String?>? = null
-
     private var scannerTimeout = false
 
+    /// Configurable variables
+    var scanWindow: List<Float>? = null
+    private var detectionSpeed: DetectionSpeed = DetectionSpeed.NO_DUPLICATES
+    private var detectionTimeout: Long = 250
     private var returnImage = false
 
-    private var scanner = BarcodeScanning.getClient()
-
     /**
      * callback for the camera. Every frame is passed through this function.
      */
@@ -87,10 +69,10 @@ class MobileScanner(
 
                 val barcodeMap: MutableList<Map<String, Any?>> = mutableListOf()
 
-                for ( barcode in barcodes) {
-                    if(scanWindow != null) {
-                        val match = isbarCodeInScanWindow(scanWindow!!, barcode, imageProxy)
-                        if(!match) {
+                for (barcode in barcodes) {
+                    if (scanWindow != null) {
+                        val match = isBarcodeInScanWindow(scanWindow!!, barcode, imageProxy)
+                        if (!match) {
                             continue
                         } else {
                             barcodeMap.add(barcode.data)
@@ -126,7 +108,11 @@ class MobileScanner(
 
     // scales the scanWindow to the provided inputImage and checks if that scaled
     // scanWindow contains the barcode
-    private fun isbarCodeInScanWindow(scanWindow: List<Float>, barcode: Barcode, inputImage: ImageProxy): Boolean {
+    private fun isBarcodeInScanWindow(
+        scanWindow: List<Float>,
+        barcode: Barcode,
+        inputImage: ImageProxy
+    ): Boolean {
         val barcodeBoundingBox = barcode.boundingBox ?: return false
 
         val imageWidth = inputImage.height

+package dev.steenbakker.mobile_scanner
+
+import dev.steenbakker.mobile_scanner.objects.MobileScannerStartParameters
+
+typealias MobileScannerCallback = (barcodes: List<Map<String, Any?>>, image: ByteArray?, width: Int?, height: Int?) -> Unit
+typealias AnalyzerCallback = (barcodes: List<Map<String, Any?>>?) -> Unit
+typealias MobileScannerErrorCallback = (error: String) -> Unit
+typealias TorchStateCallback = (state: Int) -> Unit
+typealias MobileScannerStartedCallback = (parameters: MobileScannerStartParameters) -> Unit
\ No newline at end of file

+package dev.steenbakker.mobile_scanner
+
+class NoCamera : Exception()
+class AlreadyStarted : Exception()
+class AlreadyStopped : Exception()
+class TorchError : Exception()
+class CameraError : Exception()
+class TorchWhenStopped : Exception()
+class ZoomWhenStopped : Exception()
+class ZoomNotInRange : Exception()
\ No newline at end of file

@@ -230,6 +230,6 @@ class MobileScannerHandler(
     }
 
     private fun updateScanWindow(call: MethodCall) {
-        mobileScanner!!.scanWindow = call.argument<List<Float>>("rect")
+        mobileScanner!!.scanWindow = call.argument<List<Float>?>("rect")
     }
 }
\ No newline at end of file

@@ -56,6 +56,12 @@ class MobileScanner extends StatefulWidget {
   /// [BoxFit]
   final Rect? scanWindow;
 
+  /// Only set this to true if you are starting another instance of mobile_scanner
+  /// right after disposing the first one, like in a PageView.
+  ///
+  /// Default: false
+  final bool startDelay;
+
   /// Create a new [MobileScanner] using the provided [controller]
   /// and [onBarcodeDetected] callback.
   const MobileScanner({
@@ -67,6 +73,7 @@ class MobileScanner extends StatefulWidget {
     this.onScannerStarted,
     this.placeholderBuilder,
     this.scanWindow,
+    this.startDelay = false,
     super.key,
   });
 
@@ -88,7 +95,7 @@ class _MobileScannerState extends State<MobileScanner>
 
   MobileScannerException? _startException;
 
-  Widget __buildPlaceholderOrError(BuildContext context, Widget? child) {
+  Widget _buildPlaceholderOrError(BuildContext context, Widget? child) {
     final error = _startException;
 
     if (error != null) {
@@ -104,18 +111,28 @@ class _MobileScannerState extends State<MobileScanner>
   }
 
   /// Start the given [scanner].
-  void _startScanner(MobileScannerController scanner) {
+  Future<void> _startScanner() async {
+    if (widget.startDelay) {
+      await Future.delayed(const Duration(seconds: 1, milliseconds: 500));
+    }
+
     if (!_controller.autoStart) {
       debugPrint(
         'mobile_scanner: not starting automatically because autoStart is set to false in the controller.',
       );
       return;
     }
-    scanner.start().then((arguments) {
+
+    _barcodesSubscription = _controller.barcodes.listen(
+      widget.onDetect,
+    );
+
+    _controller.start().then((arguments) {
       // ignore: deprecated_member_use_from_same_package
       widget.onStart?.call(arguments);
       widget.onScannerStarted?.call(arguments);
     }).catchError((error) {
+      debugPrint('mobile_scanner: $error');
       if (mounted) {
         setState(() {
           _startException = error as MobileScannerException;
@@ -129,14 +146,7 @@ class _MobileScannerState extends State<MobileScanner>
     super.initState();
     WidgetsBinding.instance.addObserver(this);
     _controller = widget.controller ?? MobileScannerController();
-
-    _barcodesSubscription = _controller.barcodes.listen(
-      widget.onDetect,
-    );
-
-    if (!_controller.isStarting) {
-      _startScanner(_controller);
-    }
+    _startScanner();
   }
 
   @override
@@ -149,7 +159,7 @@ class _MobileScannerState extends State<MobileScanner>
     switch (state) {
       case AppLifecycleState.resumed:
         _resumeFromBackground = false;
-        _startScanner(_controller);
+        _startScanner();
         break;
       case AppLifecycleState.paused:
         _resumeFromBackground = true;
@@ -228,7 +238,7 @@ class _MobileScannerState extends State<MobileScanner>
           valueListenable: _controller.startArguments,
           builder: (context, value, child) {
             if (value == null) {
-              return __buildPlaceholderOrError(context, child);
+              return _buildPlaceholderOrError(context, child);
             }
 
             if (widget.scanWindow != null && scanWindow == null) {
@@ -238,6 +248,7 @@ class _MobileScannerState extends State<MobileScanner>
                 value.size,
                 Size(constraints.maxWidth, constraints.maxHeight),
               );
+
               _controller.updateScanWindow(scanWindow!);
             }
 
@@ -268,8 +279,10 @@ class _MobileScannerState extends State<MobileScanner>
 
   @override
   void dispose() {
+    _controller.updateScanWindow(null);
     WidgetsBinding.instance.removeObserver(this);
     _barcodesSubscription?.cancel();
+    _barcodesSubscription = null;
     _controller.dispose();
     super.dispose();
   }

@@ -20,20 +20,7 @@ class MobileScannerController {
     @Deprecated('Instead, use the result of calling `start()` to determine if permissions were granted.')
         this.onPermissionSet,
     this.autoStart = true,
-  }) {
-    // In case a new instance is created before calling dispose()
-    if (controllerHashcode != null) {
-      stop();
-    }
-    controllerHashcode = hashCode;
-    events = _eventChannel
-        .receiveBroadcastStream()
-        .listen((data) => _handleEvent(data as Map));
-  }
-
-  /// The hashcode of the controller to check if the correct object is mounted.
-  /// Must be static to keep the same value on new instances
-  static int? controllerHashcode;
+  });
 
   /// Select which camera should be used.
   ///
@@ -84,7 +71,7 @@ class MobileScannerController {
   Function(bool permissionGranted)? onPermissionSet;
 
   /// Listen to events from the platform specific code
-  late StreamSubscription events;
+  StreamSubscription? events;
 
   /// A notifier that provides several arguments about the MobileScanner
   final ValueNotifier<MobileScannerArguments?> startArguments =
@@ -164,6 +151,11 @@ class MobileScannerController {
 
     isStarting = true;
 
+    events?.cancel();
+    events = _eventChannel
+        .receiveBroadcastStream()
+        .listen((data) => _handleEvent(data as Map));
+
     // Check authorization status
     if (!kIsWeb) {
       final MobileScannerState state = MobileScannerState
@@ -327,11 +319,8 @@ class MobileScannerController {
   /// If you call this, you cannot use this controller object anymore.
   void dispose() {
     stop();
-    events.cancel();
+    events?.cancel();
     _barcodesController.close();
-    if (hashCode == controllerHashcode) {
-      controllerHashcode = null;
-    }
   }
 
   /// Handles a returning event from the platform side
@@ -394,9 +383,13 @@ class MobileScannerController {
     }
   }
 
-  /// updates the native scanwindow
-  Future<void> updateScanWindow(Rect window) async {
-    final data = [window.left, window.top, window.right, window.bottom];
+  /// updates the native ScanWindow
+  Future<void> updateScanWindow(Rect? window) async {
+    List? data;
+    if (window != null) {
+      data = [window.left, window.top, window.right, window.bottom];
+    }
+
     await _methodChannel.invokeMethod('updateScanWindow', {'rect': data});
   }
 }