swift - 用于条件绑定的 Swift Initializer 必须具有 Optional 类型，而不是 '[AVCaptureDevice]'

Question

我的 swift 项目中有以下代码

if let availabeDevices = AVCaptureDevice.DiscoverySession(deviceTypes: [.builtInMicrophone,
.builtInWideAngleCamera], mediaType: AVMediaType.video, position: .back).devices {

            captureDevice = availabeDevices.first
        }

当我运行此代码时，它在 if 行上显示错误：

Initializer for conditional binding must have Optional type, not '[AVCaptureDevice]'

我尝试?在之后添加.devices，但这给出了这个错误：

Cannot use optional chaining on non-optional value of type '[AVCaptureDevice]'

我该怎么办？

Answer 1

使用下面的行。

if let captureDevice = AVCaptureDevice.DiscoverySession(deviceTypes: [.builtInMicrophone, .builtInWideAngleCamera], 
mediaType: AVMediaType.video, 
position: .back).devices.first {
            self.captureDevice = captureDevice
        }

Answer 2

在这里解释你的错误：

您收到错误是因为AVCaptureDevice.DiscoverySession(deviceTypes: [.builtInMicrophone, .builtInWideAngleCamera], mediaType: AVMediaType.video, position: .back).devices返回[AVCaptureDevice]的不是Optional，如果您想使用if letthenRHS应该是 always Optional。

如果你想摆脱这个错误，你需要在它AVCaptureDevice.DiscoverySession(deviceTypes: [.builtInMicrophone, .builtInWideAngleCamera], mediaType: AVMediaType.video, position: .back).devices的末尾Optional添加。as? [AVCaptureDevice]

您的代码将是：

if let availabeDevices = AVCaptureDevice.DiscoverySession(deviceTypes: [.builtInMicrophone,
                                                                            .builtInWideAngleCamera], mediaType: AVMediaType.video, position: .back).devices as? [AVCaptureDevice] {

    let captureDevice = availabeDevices.first
}