fix(ios): Fix for a possible crash when changing devices and changing focus. If the new device resets the focus, "defocusing" might not be possible if the new device does not support auto focus. For this reason, we need to do a different cleanup on the focus and exposed flags and events. (#2557)

ios/RN/RNCamera.m

@@ -310,6 +310,37 @@ BOOL _recordRequested = NO;
     [device unlockForConfiguration];
 }
 
+// Function to cleanup focus listeners and variables on device
+// change. This is required since "defocusing" might not be
+// possible on the new device, and our device reference will be
+// different
+- (void)cleanupFocus:(AVCaptureDevice*) previousDevice {
+    
+    self.isFocusedOnPoint = NO;
+    self.isExposedOnPoint = NO;
+    
+    // cleanup listeners if we had any
+    if(previousDevice != nil){
+        
+        // remove event listener
+        [[NSNotificationCenter defaultCenter] removeObserver:self name:AVCaptureDeviceSubjectAreaDidChangeNotification object:previousDevice];
+        
+        // cleanup device flags
+        NSError *error = nil;
+        if (![previousDevice lockForConfiguration:&error]) {
+            if (error) {
+                RCTLogError(@"%s: %@", __func__, error);
+            }
+            return;
+        }
+        
+        previousDevice.subjectAreaChangeMonitoringEnabled = NO;
+        
+        [previousDevice unlockForConfiguration];
+        
+    }
+}
+
 - (void)defocusPointOfInterest
 {
     AVCaptureDevice *device = [self.videoCaptureDeviceInput device];
@@ -1172,20 +1203,28 @@ BOOL _recordRequested = NO;
             return;
         }
 
+        
+        // Do additional cleanup that might be needed on the
+        // previous device, if any.
+        AVCaptureDevice *previousDevice = self.videoCaptureDeviceInput != nil ? self.videoCaptureDeviceInput.device : nil;
 
-        // setup our capture preset based on what was set from RN
-        // and our defaults
-        // if the preset is not supported (e.g., when switching cameras)
-        // canAddInput below will fail
-        self.session.sessionPreset = [self getDefaultPreset];
-
-
+        [self cleanupFocus:previousDevice];
+        
+        
+        // Remove inputs
         [self.session removeInput:self.videoCaptureDeviceInput];
 
         // clear this variable before setting it again.
         // Otherwise, if setting fails, we end up with a stale value.
         // and we are no longer able to detect if it changed or not
         self.videoCaptureDeviceInput = nil;
+        
+        // setup our capture preset based on what was set from RN
+        // and our defaults
+        // if the preset is not supported (e.g., when switching cameras)
+        // canAddInput below will fail
+        self.session.sessionPreset = [self getDefaultPreset];
+        
 
         if ([self.session canAddInput:captureDeviceInput]) {
             [self.session addInput:captureDeviceInput];