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我正在swift中下载文件，并且下载会话由每个表格视图单元格上的按钮触发。但是，我不希望下一次下载（如果有人按下另一个单元格上的下载按钮）发生，直到上一次完成。下载在Swift中完成后发送？
有没有办法让我可以使用像dispatch_after这样的东西来实现这一点？
这里是我的代码下载发生，如果它有帮助。
//FUNCTION TO DOWNLOAD THE PDF
//PASS THE ONLINE PDF URL AS NSURL
//ASYNC REQUEST
let defaultSession = NSURLSession(configuration: NSURLSessionConfiguration.defaultSessionConfiguration())
var dataTask: NSURLSessionDataTask?
var temp_name = String()
var temp_index = Int()
var temp_indexPath = NSIndexPath()
lazy var downloadsSession: NSURLSession = {
let configuration = NSURLSessionConfiguration.defaultSessionConfiguration()
let session = NSURLSession(configuration: configuration, delegate: self, delegateQueue: nil)
return session
}()
func getUrl(name: String) -> NSURL?{
let documentsUrl = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask).first as NSURL!
return documentsUrl.URLByAppendingPathComponent(name)
}
func getIndex() -> Int?{
return temp_index
}
func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didFinishDownloadingToURL location: NSURL) {
if let originalURL = downloadTask.originalRequest?.URL?.absoluteString,
destinationURL = getUrl(temp_name){
let fileManager = NSFileManager.defaultManager()
do {
try fileManager.removeItemAtURL(destinationURL)
} catch {
// Non-fatal: file probably doesn't exist
}
do {
try fileManager.copyItemAtURL(location, toURL: destinationURL)
} catch let error as NSError {
print("Could not copy file to disk: \(error.localizedDescription)")
}
}
if let url = downloadTask.originalRequest?.URL?.absoluteString {
activeDownloads[url] = nil
if let trackIndex = getIndex() {
dispatch_async(dispatch_get_main_queue(), {
defaults.setBool(false, forKey: self.temp_name + "_downloading")
self.tableView.reloadRowsAtIndexPaths([NSIndexPath(forRow: trackIndex, inSection: 0)], withRowAnimation: .None)
})
}
}
}
func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) {
if let downloadUrl = downloadTask.originalRequest?.URL?.absoluteString,
download = activeDownloads[downloadUrl] {
download.progress = Float(totalBytesWritten)/Float(totalBytesExpectedToWrite)
if let trackIndex = getIndex(), let cell = tableView.cellForRowAtIndexPath(NSIndexPath(forRow: trackIndex, inSection: 0)) as? MainTableViewCell {
dispatch_async(dispatch_get_main_queue(), {
cell.progress.progress = download.progress
if(download.progress < 1.0){
cell.progress.hidden = false
}
else{
cell.progress.hidden = true
}
})
}
}
}
// Action triggered by UIButton (in this case the download button)
//Access tag, which is the IndexPath.row, using sender.tag
@IBAction func downloadFile(sender: UIButton){
let indexPath = NSIndexPath(forRow: sender.tag, inSection: 0)
let cell = tableView.cellForRowAtIndexPath(indexPath) as! MainTableViewCell
cell.downloadButton.hidden = true
cell.progress.progress = 0
cell.progress.hidden = false
let isAvailable = true
let key = names[sender.tag] + "_offline"
defaults.setValue(isAvailable, forKey: key)
let name = (names[sender.tag])
let fileName = name + ".pdf"
let attachment = attachments[sender.tag]
temp_name = fileName
temp_index = sender.tag
temp_indexPath = indexPath
let destinationURL = getUrl(temp_name)!
defaults.setValue(destinationURL.path!, forKey: name + "_path")
defaults.synchronize()
defaults.setBool(true, forKey: name + "_downloading")
let urlString = attachment
let url = NSURL(string: urlString)
let download = PDFDownload(url: urlString)
download.downloadTask = downloadsSession.downloadTaskWithURL(url!)
download.downloadTask!.resume()
download.isDownloading = true
activeDownloads[download.url] = download
}
有一个布尔值用于存储是否正在进行下载会话，所以也许有一种方法可以使用它？等到布尔值为false来执行我的代码？
您可以在第一次点击按钮后禁用按钮，并在网络调用的完成处理程序中重新启用它 –
让我澄清 - 它们是每个表格视图单元格上的按钮，我仍然希望其他一些工作，但只是等到开始下载 –
啊，你可以做的一件事就是使用一个串行dispatch_queue，或者你可以把它包装在一个NSOperation中，并使用一个串行NSOperation队列 –