ios - fatal error : unexpectedly found nil while unwrapping an Optional value in AVFoundation

Question

我正在制作一个使用闪光灯作为手电筒的应用程序。我正在编写以下代码，XCode 在第一行就给我错误。任何人都可以提出它的根本原因吗？我已完成调试，但似乎无法找到它..

@IBAction func powerButton(sender: UIButton)
    {
        NSLog("flashButtonClicked")

        let flashLight : AVCaptureDevice = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo)!

        torchButton.setBackgroundImage(switchOnImage, forState:UIControlState.Normal)
        NSLog("Button Background changed!!")

        if flashLight.torchAvailable && flashLight.isTorchModeSupported(AVCaptureTorchMode.On)
        {
            NSLog("inside if...")
            let success = flashLight.lockForConfiguration(nil)

            if (success)
            {
                if flashLight.torchActive
                {
                    flashLight.isTorchModeSupported(AVCaptureTorchMode.Off)
                    onOffbutton.setBackgroundImage(switchOffImage, forState:UIControlState.Normal)
                }
                else
                {
                    flashLight.setTorchModeOnWithLevel(100, error: nil)
                    onOffbutton.setBackgroundImage(switchOnImage, forState:UIControlState.Normal)
                }
                flashLight.unlockForConfiguration()
            }
        }
    }

Answer 1

AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo) 返回一个 nil 对象。您正在尝试解包它 (!) 并将其分配给不可为空的常量 let flashLight : AVCaptureDevice

尝试添加 nil 的检查

var flashLight = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo)
if flashLight != nil {
    //rest of your code here
}