是否有可能知道QLPreviewController何时到达文档的末尾？

class PreviewControllerDelegate: NSObject, QLPreviewControllerDelegate {
    func previewController(_ controller: QLPreviewController, didUpdateContentsOf previewItem: QLPreviewItem) {
        let currentIndex = controller.currentPreviewItemIndex
        let totalItems = controller.previewItems.count
        
        if currentIndex == totalItems - 1 {
            // 到达文档末尾
            print("已到达文档末尾")
        }
    }
}

// 在使用QLPreviewController的地方设置代理
let previewController = QLPreviewController()
previewController.delegate = PreviewControllerDelegate()