feat: add available camera information in startcallback on android

@@ -240,6 +240,7 @@ class MobileScanner(
 
         cameraProviderFuture.addListener({
             cameraProvider = cameraProviderFuture.get()
+            val nrOfCameras = cameraProvider?.availableCameraInfos?.size
 
             if (cameraProvider == null) {
                 mobileScannerErrorCallback(CameraError())
@@ -340,7 +341,8 @@ class MobileScanner(
                     if (portrait) width else height,
                     if (portrait) height else width,
                     camera?.cameraInfo?.hasFlashUnit() ?: false,
-                    textureEntry!!.id()
+                    textureEntry!!.id(),
+                    nrOfCameras ?: 0
                 )
             )
         }, executor)

@@ -178,7 +178,8 @@ class MobileScannerHandler(
                     result.success(mapOf(
                         "textureId" to it.id,
                         "size" to mapOf("width" to it.width, "height" to it.height),
-                        "torchable" to it.hasFlashUnit
+                        "torchable" to it.hasFlashUnit,
+                        "nrOfCameras" to it.nrOfCameras
                     ))
                 }
             },

@@ -4,5 +4,6 @@ class MobileScannerStartParameters(
     val width: Double = 0.0,
     val height: Double,
     val hasFlashUnit: Boolean,
-    val id: Long
+    val id: Long,
+    val nrOfCameras: Int
 )
\ No newline at end of file

@@ -47,6 +47,8 @@ class _BarcodeScannerWithControllerState
     }
   }
 
+  int? nrOfCameras;
+
   @override
   Widget build(BuildContext context) {
     return Scaffold(
@@ -57,6 +59,12 @@ class _BarcodeScannerWithControllerState
           return Stack(
             children: [
               MobileScanner(
+                onScannerStarted: (arguments) {
+                  if (arguments?.nrOfCameras != null) {
+                    nrOfCameras = arguments!.nrOfCameras;
+                    setState(() {});
+                  }
+                },
                 controller: controller,
                 errorBuilder: (context, error, child) {
                   return ScannerErrorWidget(error: error);
@@ -146,7 +154,9 @@ class _BarcodeScannerWithControllerState
                           },
                         ),
                         iconSize: 32.0,
-                        onPressed: () => controller.switchCamera(),
+                        onPressed: nrOfCameras != null && nrOfCameras! < 2
+                            ? null
+                            : () => controller.switchCamera(),
                       ),
                       IconButton(
                         color: Colors.white,

@@ -225,12 +225,12 @@ class _MobileScannerState extends State<MobileScanner>
               return Stack(
                 alignment: Alignment.center,
                 children: [
-                  _scanner(value.size, value.webId, value.textureId),
+                  _scanner(value.size, value.webId, value.textureId, value.nrOfCameras),
                   widget.overlay!,
                 ],
               );
             } else {
-              return _scanner(value.size, value.webId, value.textureId);
+              return _scanner(value.size, value.webId, value.textureId, value.nrOfCameras);
             }
           },
         );
@@ -238,7 +238,7 @@ class _MobileScannerState extends State<MobileScanner>
     );
   }
 
-  Widget _scanner(Size size, String? webId, int? textureId) {
+  Widget _scanner(Size size, String? webId, int? textureId, int? nrOfCameras) {
     return ClipRect(
       child: LayoutBuilder(
         builder: (_, constraints) {

@@ -304,6 +304,7 @@ class MobileScannerController {
 
     isStarting = false;
     return startArguments.value = MobileScannerArguments(
+      nrOfCameras: startResult['nrOfCameras'] as int?,
       size: size,
       hasTorch: hasTorch,
       textureId: kIsWeb ? null : startResult['textureId'] as int?,

@@ -15,10 +15,15 @@ class MobileScannerArguments {
   /// The texture id of the capture used internally if device is web.
   final String? webId;
 
+  /// Indicates how many cameras are available.
+  /// Only available on Android
+  final int? nrOfCameras;
+
   MobileScannerArguments({
     required this.size,
     required this.hasTorch,
     this.textureId,
     this.webId,
+    this.nrOfCameras
   });
 }