swift4 – ‘AVCapturePhotoSettings’类型的值没有成员’availa

@objc func launchCoreML() {
    let settings = AVCapturePhotoSettings()
    let previewPixelType = settings.availablePreviewPhotoPixelFormatTypes.first
    let previewFormat = [
        kCVPixelBufferPixelFormatTypeKey as String: previewPixelType,kCVPixelBufferWidthKey as String: 160,kCVPixelBufferHeightKey as String: 160
    ] as [String : Any]

    settings.previewPhotoFormat = previewFormat
    cameraOutput.capturePhoto(with: settings,delegate: self)
}

我有一个错误说：

Value of type ‘AVCapturePhotoSettings’ has no member
‘availablePreviewPhotoPixelFormat’.

我正在使用Xcode 9的测试版.