正在更新 UI Dispatch_Async 后台下载 Swift

Question

我正在开发一个 folders/files 应用程序，用户可以在其中将文件下载到本地磁盘。每当用户下载文件时，我想显示一个显示进度的下载栏。

为此，我创建了一个协议，允许我的下载 class 和我的视图控制器进行通信：

协议：

protocol DownloadResponder : class {
    func downloadFinished()
    func downloadProgress(current:Int64, total:Int64)
}

下载class:

class fileDownloader: NSObject, NSURLSessionDelegate, NSURLSessionDownloadDelegate {

    //responder
    var responder : MyAwesomeDownloadResponder?

    init(responder : MyAwesomeDownloadResponder) {
        self.responder = responder
    }

    ...

    func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) {

        println("downloaded \(100*totalBytesWritten/totalBytesExpectedToWrite)")
        responder?.downloadProgress(totalBytesWritten, total: totalBytesExpectedToWrite)

    }

...

}

然后在我的视图控制器中我有触发 downloadProgress 函数的下载按钮：

func downloadProgress(current:Int64, total:Int64) {
        let priority = DISPATCH_QUEUE_PRIORITY_DEFAULT
        dispatch_async(dispatch_get_global_queue(priority, 0)) {
            // do some task
            var currentProgress = 100 * current / total
            dispatch_async(dispatch_get_main_queue()) {
                // update some UI
                self.downloadLbl.text = "Downloaded \(currentProgress)%"
                //set progress bar
                self.progressBar.setProgress(Float(currentProgress), animated: true)
            }
        }

    }

虽然在控制台中打印信息一直有效，但更新 UI 并不是很稳定。为了解决这个问题，我使用了 dispatch_async 方法在主线程上推送 UI 更改。然而，虽然它始终在第一次运行，但会弹回到前一个视图控制器并再次返回，再次执行下载不会触发 UI 更新。进度条 progressBar.setProgress 什么都不做，我的标签 downloadLbl.text 不会自行更新。

有没有人知道解决这个问题的方法？如果我的问题缺少信息，请告诉我，我会尝试添加现有信息。谢谢！

Answer 1

因为我没有收到/找到任何解决我问题的方法，我回到了更高的层次并改变了我的 classes 之间的通信方式以处理 ui 基于背景的变化下载线程进度。

我没有使用协议，而是使用了通知，它解决了我的问题。

里面下载class:

func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) {

        println("downloaded \(100*totalBytesWritten/totalBytesExpectedToWrite)")

        //NOTIFICATION
        // notify download progress!
        var fileInfo = [NSObject:AnyObject]()
        fileInfo["fileId"] = fileDownloader.storageInfo[downloadTask.taskIdentifier]!["id"] as! Int!
        fileInfo["fileCurrent"] = Float(totalBytesWritten)
        fileInfo["fileTotal"] = Float(totalBytesExpectedToWrite)

        let defaultCenter = NSNotificationCenter.defaultCenter()
        defaultCenter.postNotificationName("DownloadProgressNotification",
            object: nil,
            userInfo: fileInfo)

    }

在视图控制器内：

override func viewDidLoad() {
        super.viewDidLoad()

        // ready for receiving notification
        let defaultCenter = NSNotificationCenter.defaultCenter()
        defaultCenter.addObserver(self,
            selector: "handleCompleteDownload:",
            name: "DownloadProgressNotification",
            object: nil)
    }

func handleCompleteDownload(notification: NSNotification) {
        let tmp : [NSObject : AnyObject] = notification.userInfo!

        // if notification received, change label value
        var id = tmp["fileId"] as! Int!
        var current = tmp["fileCurrent"] as! Float!
        var total = tmp["fileTotal"] as! Float!
        var floatCounter = 100 * current / total
        var progressCounter = String(format: "%.f", floatCounter)

        if(id == self.fileId){
            let priority = DISPATCH_QUEUE_PRIORITY_DEFAULT
                    dispatch_async(dispatch_get_global_queue(priority, 0)) {
                        // do some task
                        dispatch_async(dispatch_get_main_queue()) {
                            // update some UI
                            self.downloadLbl.text = "Downloaded \(progressCounter)%"
                            self.progressBar.setProgress((progressCounter as NSString).floatValue, animated: true)
                        }
                    }
        }
    }

希望对您有所帮助！

正在更新 UI Dispatch_Async 后台下载 Swift

Updating UI Dispatch_Async background download Swift

user-interface

ios

background-thread

dispatch-async

swift