Swift isLockingFocusWithCustomLensPositionSupported always returns false

问题

I want to set the lens distance of my iPhoneX to a constant. In order to check if that is supported, I check the isLockingFocusWithCustomLensPositionSupported property of my device, as described in the documentation here: https://developer.apple.com/documentation/avfoundation/avcapturedevice/2361529-islockingfocuswithcustomlensposi

The method always returns false, even when the device is locked for configuration, which means that calling the method setFocusModeLocked(lensPosition, completionHandler) will alway throw an error. Why is this the case, and how to correctly call the setFocusModeLocked() ?

Below is my approach:

let device = self.deviceInput.device 
do { 
     try device.lockForConfiguration() 
     if device.isFocusPointOfInterestSupported && device.isFocusModeSupported(focusMode) 
     { 
      // this return true 
     } 
     if device.isLockingFocusWithCustomLensPositionSupported 
     { 
       //this always returns false
       device.setFocusModeLocked(lensPosition: focusDistance, completionHandler: nil) 
     } 
     device.unlockForConfiguration() 
   } catch { print("Could not lock device for configuration: \(error)") }

Tested on iPhoneX, iOS 12

来源：https://stackoverflow.com/questions/55915863/swift-islockingfocuswithcustomlenspositionsupported-always-returns-false