我已经搜索但是没有在Objective C中找到相关答案。有没有办法在Swift中找到下载文件的进度,以便向用户显示?我是iOS编程的新手,我尝试过使用NSURLSession但没有成功。
编辑: 我已经在this帖子中看到了这种方法,但我似乎无法理解如何获得进度状态:
func downloadFile(page: NSString){
finished = false
var statusCode:Int = 0
println("Download starting")
let url = NSURL(string: page)
let task = NSURLSession.sharedSession().dataTaskWithURL(url!) {(data, response, error) in
if error != nil {
println("download failed with error \(error?.localizedDescription)")
} else {
println("Expected Content-Length \(response.expectedContentLength)")
self.contentLength = response.expectedContentLength
if let httpResponse = response as? NSHTTPURLResponse {
println("Status Code of number \(self.countDownload) is \(httpResponse.statusCode)")
statusCode = httpResponse.statusCode
}
}
}
task.resume()
}
提前谢谢
答案 0 :(得分:12)
可以在
中计算进度状态URLSession(_:downloadTask:didWriteData:totalBytesWritten:totalBytesExpectedToWrite:)
这是协议 NSURLSessionDownloadDelegate 的三种必需方法之一。在我的例子中,方法的代码如下所示:
func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) {
// println("download task did write data")
let progress = Float(totalBytesWritten) / Float(totalBytesExpectedToWrite)
dispatch_async(dispatch_get_main_queue()) {
self.progressDownloadIndicator.progress = progress
}
}
我创建了一个小项目,它实现了三种不同的方法:
检查出来:http://goo.gl/veRkA7
答案 1 :(得分:4)
假设您正在下载文件,那么只有NSURLSessionTask
的子类就是NSURLSessionDownloadTask
。以下是关于特定功能的NSURLSession文档的摘录:
定期向代表通知下载进度。
func URLSession(_ session: NSURLSession, downloadTask downloadTask: NSURLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten totalBytesWritten: Int64, totalBytesExpectedToWrite totalBytesExpectedToWrite: Int64 )
例如,您可以通过执行以下操作将进度输出到控制台:
println("\(totalBytesWritten) / \(totalBytesExpectedToWrite)")
答案 2 :(得分:1)
您可以简单地观察progress
对象的URLSessionDataTask
属性。而且您无需像其他答案在这里建议的那样计算进度。 fractionCompleted
上有一个Progress
属性。
游乐场示例:
import Foundation
import PlaygroundSupport
let page = PlaygroundPage.current
page.needsIndefiniteExecution = true
let url = URL(string: "https://source.unsplash.com/random/4000x4000")!
let task = URLSession.shared.dataTask(with: url) { _, _, _ in
page.finishExecution()
}
// Don't forget to invalidate the observation when you don't need it anymore.
let observation = task.progress.observe(\.fractionCompleted) { progress, _ in
print(progress.fractionCompleted)
}
task.resume()