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

Posted 2023-02-24

【中文标题】用于条件绑定的 Swift Initializer 必须具有 Optional 类型，而不是 \'[AVCaptureDevice]\'

【英文标题】：Swift Initializer for conditional binding must have Optional type, not '[AVCaptureDevice]'用于条件绑定的 Swift Initializer 必须具有 Optional 类型，而不是 '[AVCaptureDevice]'

【发布时间】：2017-12-16 07:04:16

【问题描述】：

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，如果行显示错误：

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

我尝试在.devices 之后添加?，但出现了这个错误：

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

我该怎么办？

【参考方案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
        

【参考方案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] 而不是Optional，如果您想使用if let，那么RHS 应该始终是Optional。

如果你想摆脱这个错误，你需要将AVCaptureDevice.DiscoverySession(deviceTypes: [.builtInMicrophone, .builtInWideAngleCamera], mediaType: AVMediaType.video, position: .back).devices 设置为Optional，方法是在其末尾添加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