iOS在下载前获取文件大小

Question

我找不到适合我的解决方案。但是我需要获取我正在下载的视频的文件大小，以便我可以确保用户在他的手机上有足够的空间来下载它。

我的想法是检查视频的大小，如果用户有空间，我会下载它。有什么建议吗？

NSURL *url = [NSURL URLWithString:stringURL];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
NSURLSession *session = [NSURLSession sharedSession];

NSURLSessionDownloadTask *downloadTask = [session downloadTaskWithRequest:request completionHandler:^(NSURL *location, NSURLResponse *response, NSError *error) {...}];

Answer 1

这是其他答案的变体，它使用函数（在 Swift 4 中）在检索大小时调用闭包：

func getDownloadSize(url: URL, completion: @escaping (Int64, Error?) -> Void) {
    let timeoutInterval = 5.0
    var request = URLRequest(url: url,
                             cachePolicy: .reloadIgnoringLocalAndRemoteCacheData,
                             timeoutInterval: timeoutInterval)
    request.httpMethod = "HEAD"
    URLSession.shared.dataTask(with: request) { (data, response, error) in
        let contentLength = response?.expectedContentLength ?? NSURLSessionTransferSizeUnknown
        completion(contentLength, error)
    }.resume()
}

这个函数的使用方法如下：

let url = URL(string: "https://upload.wikimedia.org/wikipedia/commons/7/70/Example.png")!
getDownloadSize(url: url, completion: { (size, error) in
    if error != nil {
        print("An error occurred when retrieving the download size: \(error.localizedDescription)")
    } else {
        print("The download size is \(size).")
    }
})

Answer 2

斯威夫特 3： 由于您正在调用 dataTask ，因此您不能在块之外使用该值，因此请以这种方式使用它。

 var contentLength: Int64 = NSURLSessionTransferSizeUnknown
                let request = NSMutableURLRequest(url: url as URL, cachePolicy: NSURLRequest.CachePolicy.reloadIgnoringLocalAndRemoteCacheData, timeoutInterval: 30.0);
                request.httpMethod = "HEAD";
                request.timeoutInterval = 5;
                let group = DispatchGroup()
                group.enter()
                URLSession.shared.dataTask(with: request as URLRequest, completionHandler: { (data, response, error) -> Void in
                    contentLength = response?.expectedContentLength ?? NSURLSessionTransferSizeUnknown
//Here you should use the value
                    print("contentLength",contentLength)
                    group.leave()
                }).resume()

Answer 3

使用此函数获取 URL 的远程大小。请注意这个函数是同步的并且会阻塞线程，所以从不同于主线程的线程中调用它：

extension NSURL {
    var remoteSize: Int64 {
        var contentLength: Int64 = NSURLSessionTransferSizeUnknown
        let request = NSMutableURLRequest(URL: self, cachePolicy: NSURLRequestCachePolicy.ReloadIgnoringLocalAndRemoteCacheData, timeoutInterval: 30.0);
        request.HTTPMethod = "HEAD";
        request.timeoutInterval = 5;
        let group = dispatch_group_create()
        dispatch_group_enter(group)
        NSURLSession.sharedSession().dataTaskWithRequest(request, completionHandler: { (data, response, error) -> Void in
            contentLength = response?.expectedContentLength ?? NSURLSessionTransferSizeUnknown
            dispatch_group_leave(group)
        }).resume()
        dispatch_group_wait(group, dispatch_time(DISPATCH_TIME_NOW, Int64(5 * NSEC_PER_SEC)))
        return contentLength
    }
}

然后在与主线程不同的线程上随处调用 remoteSize 变量：

let size = url.remoteSize

Answer 4

SWIFT 3：

extension NSURL {
    var remoteSize: Int64 {
        var contentLength: Int64 = NSURLSessionTransferSizeUnknown
        let request = NSMutableURLRequest(url: self as URL, cachePolicy: NSURLRequest.CachePolicy.reloadIgnoringLocalAndRemoteCacheData, timeoutInterval: 30.0);
        request.httpMethod = "HEAD";
        request.timeoutInterval = 5;
        let group = DispatchGroup()
        group.enter()
        URLSession.shared.dataTask(with: request as URLRequest, completionHandler: { (data, response, error) -> Void in
            contentLength = response?.expectedContentLength ?? NSURLSessionTransferSizeUnknown
            group.leave()
        }).resume()

        return contentLength
    }
}