[camera] Solves delay when using the zoom feature on iOS.

packages/camera/camera/example/lib/main.dart

@@ -56,9 +56,6 @@ class _CameraExampleHomeState extends State<CameraExampleHome>
   double _currentScale = 1.0;
   double _baseScale = 1.0;
 
-  // Counting pointers (number of user fingers on screen)
-  int _pointers = 0;
-
   @override
   void initState() {
     super.initState();
@@ -171,21 +168,17 @@ class _CameraExampleHomeState extends State<CameraExampleHome>
         ),
       );
     } else {
-      return Listener(
-        onPointerDown: (_) => _pointers++,
-        onPointerUp: (_) => _pointers--,
-        child: CameraPreview(
-          controller,
-          child: LayoutBuilder(
-              builder: (BuildContext context, BoxConstraints constraints) {
-            return GestureDetector(
-              behavior: HitTestBehavior.opaque,
-              onScaleStart: _handleScaleStart,
-              onScaleUpdate: _handleScaleUpdate,
-              onTapDown: (details) => onViewFinderTap(details, constraints),
-            );
-          }),
-        ),
+      return CameraPreview(
+        controller,
+        child: LayoutBuilder(
+            builder: (BuildContext context, BoxConstraints constraints) {
+          return GestureDetector(
+            behavior: HitTestBehavior.opaque,
+            onScaleStart: _handleScaleStart,
+            onScaleUpdate: _handleScaleUpdate,
+            onTapDown: (details) => onViewFinderTap(details, constraints),
+          );
+        }),
       );
     }
   }
@@ -196,7 +189,7 @@ class _CameraExampleHomeState extends State<CameraExampleHome>
 
   Future<void> _handleScaleUpdate(ScaleUpdateDetails details) async {
     // When there are not exactly two fingers on screen don't scale
-    if (_pointers != 2) {
+    if (details.pointerCount != 2) {
       return;
     }