从'[AVCaptureDevice]'到'[AVCaptureDevice]'的条件转换总是成功的.黄色警告

错误消息表明您有条件地将非可选类型强制转换为冗余的可选类型.

⌥-click在devices检查其声明

class func devices() -> [AVCaptureDevice]

所以很简单

let devices = AVCaptureDevice.devices()
// Loop through all the capture devices on this phone
for device in devices { ...