ios - 使用文件管理器创建文件时如何在 UI 中显示事件指示器

Question

我正在从远程服务器下载文件(.pdf、.JPG、.PNG 等)。 “fullFileURLString”是以字符串形式提供文件路径 URL。

当用户从 Collection View 中单击文件名时，我需要提供将文件保存在用户自己的设备中的选项。为此，我正在使用 UIDocumentInteractionController()。我计划向用户提供此功能。

此功能运行正常。这个过程需要一些时间才能完成。我想在这个过程发生时显示事件指示器。但事件指示器没有动画或没有显示在 View 上。

如何在该过程发生时显示事件指示器并在 documentInteractionController 存在时隐藏事件指示器？

我尝试过下面的代码

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier:"showUplodedMediaCellCollectionViewCell", for: indexPath) as! showUplodedMediaCellCollectionViewCell;
        if let bytes = Memory().deviceRemainingFreeSpaceInBytes() {
            let twoHundresMb:Int64 = 283115520
            if bytes < twoHundresMb {
                Alert.showAlertView(on: self, message: "There is not enough available storage to download.")
            }
            else {
                let activityIndicatior:UIActivityIndicatorView = UIActivityIndicatorView()
                activityIndicatior.center = self.view.center
                activityIndicatior.hidesWhenStopped = true
                activityIndicatior.style = .gray
                view.addSubview(activityIndicatior)
                activityIndicatior.startAnimating()
                let mediaDetails = MediaFiles?[indexPath.row]
                if let path = mediaDetails?.folderPath {
                    if let Filename = mediaDetails?.name {
                     let fullFileURLString = "\(baseURL)"+"\(path)"+"\(Filename)"
                        if let FileUrl = URL(string: fullFileURLString) {
                            let Filedata = try? Data(contentsOf: FileUrl)
                            let documentDirectoryPath = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0] as String
                            let documentDirectoryPath2 = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0] as NSString
                            let documentDirectoryPathURL = NSURL(fileURLWithPath: documentDirectoryPath)

                            if let pathComponent = documentDirectoryPathURL.appendingPathComponent(Filename) {
                                let fileManager = FileManager.default
                                let filePath = pathComponent.path
                                if fileManager.fileExists(atPath: filePath) {
                                    print("Already Have:",Filename)
                                }
                                else {
                                    print("No available",Filename)
                                    let fileManager = FileManager.default
                                    let fileManagerPath = documentDirectoryPath2.appendingPathComponent(Filename)
                                    fileManager.createFile(atPath: fileManagerPath, contents: Filedata, attributes: nil)
                                    print("path:- \(fileManagerPath)")
                                }
                            }

                            let destinationPath = documentDirectoryPath2.appendingPathComponent(Filename)
                            let destinationURL = URL(fileURLWithPath: destinationPath)
                            let dowanloadedMediaDocumentDirectoryPathURL = NSURL(fileURLWithPath: documentDirectoryPath)

                            if let pathComponent = dowanloadedMediaDocumentDirectoryPathURL.appendingPathComponent(Filename) {
                                let fileManager = FileManager.default
                                let filePath = pathComponent.path
                                if fileManager.fileExists(atPath: filePath) {
                                    activityIndicatior.stopAnimating()
                                    var documentInteractionController = UIDocumentInteractionController()
                                    documentInteractionController.url = destinationURL
                                    if !documentInteractionController.presentOpenInMenu(from: cell.bounds, in: view, animated: true) {
                                        print("You don't have an app installed that can handle ePub files.")

                                    }
                                }
                                else {
                                    Alert.showAlertView(on: self, message: "Unable to download file from remote server.")
                                }
                            }
                        }
                    }
                }
             }
        }
        else {
            Alert.showAlertView(on: self, message: "There is not enough available storage to download.")
        }
    }

我希望 ActivityIndi​​cator 会一直显示动画，直到 documentInteractionController 不再出现。

Answer 1

您应该将所有下载文件过程放在后台线程中。

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {

    // Some code here

    DispatchQueue.main.async {
        activityIndicatior.startAnimating()
    }

    DispatchQueue.global(qos: .userInitiated).async {  
        // Download file or perform expensive task

        DispatchQueue.main.async {
            activityIndicator.stopAnimating()
        }
    }
}

将您的代码拆分为具有单一职责的函数，这将使您的代码更易于调试。