AVCaptureTorchModeAuto不会持续更新割炬模式(AVCaptureTorchModeAuto does not continuously update torch mode)

 我正在编写一个应用程序，根据照明条件自动打开iOS设备背面的手电筒。 该应用程序呈现实时摄像机视图，但不记录视频。 
 
 我尝试过使用AVCaptureTorchModeAuto ，但它似乎只是在捕获会话开始时测量图像的亮度，并相应地设置割炬。 无论相机图像的亮度如何，之后设置都不会改变。 
 
 系统可以连续调整割炬，如文档中所述 ？ 
 
 
 
 捕获设备持续监控光照水平，并在必要时使用割炬。 
 
 
 适用于iOS 4.0及更高版本。 
 

I am writing an app that automatically turns on the torch on the back of an iOS device depending on lighting conditions. The app renders a live camera view, and does not record the video.
 
I have tried using AVCaptureTorchModeAuto, but it only seems to measure the brightness of the image at the start of the capture session, and set the torch accordingly. The setting then does not change afterwards, regardless of the brightness of the camera image.
 
It is possible to have the system adjust the torch continuously, like stated in the documentation?
 
 
 
The capture device continuously monitors light levels and uses the torch when necessary.
 
 
Available in iOS 4.0 and later.
 

原文：https://stackoverflow.com/questions/22998471