使用 SwiftUI 显示 SessionDownloadDelegate 的进度

Question

我正在尝试使用 SwiftUI 组合一个杂志浏览应用程序，但在尝试创建下载进度指示器时遇到了障碍。我似乎无法找到一种方法来使ProgressBar我从urlSession(didWriteData)in进行更新URLSessionDownloadDelegate。

我有一个DownloadManager作为环境对象传递给主视图的单曲，它处理所有杂志问题的下载。

class DownloadManager: NSObject, URLSessionDownloadDelegate, ObservableObject {

    var activeDownloads: [URL: Download] = [:]

    lazy var downloadSession: URLSession = {
        let config = URLSessionConfiguration.default
        return URLSession(configuration: config, delegate: self, delegateQueue: nil)
    }()

    /*downloading and saving the issues is handled here*/

    func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) {
        guard
            let url = downloadTask.originalRequest?.url,
            let download = activeDownloads[url]
            else {
                return
        }
        //this is the value that needs to be indicated by the UI
        download.progress = (Float(totalBytesWritten) / Float(totalBytesExpectedToWrite))
    }

}

自定义Download类包含以下内容：

class Download {

    var issue: Issue
    var url: URL

    var progress: Float = 0.0

    var task: URLSessionDownloadTask?
    var resumeData: Data?

    init(issue: Issue) {
        self.issue = issue
        self.url = issue.webLocation
    }

}

要下载的可用问题显示在 a 中的行中List，并且在下载它们时，进度应该由ProgressBar. 行布局代码的相关部分在这里：

struct IssueRow: View {

    var issue: Issue

    @EnvironmentObject var downloadManager: DownloadManager
    @State var downloadProgress: Float = 0.0

    var body: some View {

        //the progress bar that needs to continuously update
        ProgressBar(value: $downloadProgress)
            .frame(height: 4)

    }

    private func downloadIssue() {
        downloadManager.startDownload(issue: issue)
        downloadProgress = downloadManager.activeDownloads[issue.webLocation]!.progress
        //This does not actually change as the download progresses
    }

在内部ProgressBar，进度存储为@Binding浮点数。

struct ProgressBar: View {

    @Binding var value: Float

    var body: some View {
        GeometryReader { geometry in
            ZStack(alignment: .leading) {
                Rectangle().frame(width: geometry.size.width, height:
                    geometry.size.height)
                    .opacity(0.3)
                    .foregroundColor(Color(UIColor.systemTeal))
                Rectangle().frame(width: CGFloat(self.value)*geometry.size.width, height: geometry.size.height)
                    .foregroundColor(Color.navy)
                    .animation(.linear)
            }
        }
    }
}

我真的不确定如何将 SwiftUI 的行为及其各种元素与 Swift 中的旧东西同步。任何帮助是极大的赞赏！

Answer 1

该方法是在您的下载中注入进度回调闭包并将其用作桥梁。

1) 在下载

class Download {

    var issue: Issue
    var url: URL
    var callback: (Float) -> ()    // << here !!

    var progress: Float = 0.0 {
       didSet {
          self.callback(progress)    // << here !!
       }
    }

    // ... other your code here ...
}

2) 在 SwiftUI 中

private func downloadIssue() {
    downloadManager.startDownload(issue: issue) { value in // << here !!
      DispatchQueue.main.async {
        self.downloadProgress = value // make sure on main queue
      }
    }
}

3）在startDownload（未提供）将回调闭包传递到创建的Download实例中，例如（只是沙哑）

func startDownload(issue: Issue, progress: @escaping (Float) -> ()) {

   let download = Download(issue: issue, url: issue.url, callback: progress)
   ...
}