Question

我想在下载之前从网址获取文件大小

这是obj-c代码

    NSURL *URL = [NSURL URLWithString:"ExampleURL"];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:URL];
    [request setHTTPMethod:@"HEAD"];
    NSHTTPURLResponse *response;
    [NSURLConnection sendSynchronousRequest:request returningResponse:&response error: nil];
    long long size = [response expectedContentLength];

这里是Swift Code

var url:NSURL = NSURL(string: "ExmapleURL")
                var request:NSMutableURLRequest = NSMutableURLRequest(URL: url)
                request.HTTPMethod = "HEAD"
                var response = NSHTTPURLResponse()
                NSURLConnection.sendSynchronousRequest(request, returningResponse: &response , error: nil)

但我在这里有错误

NSURLConnection.sendSynchronousRequest(request, returningResponse: &response , error: nil)

'NSHTTPURLResponse' is not identical to 'NSURLResponse?'

我在这里错过了什么东西？

Answer 1

响应参数的类型为

AutoreleasingUnsafeMutablePointer<NSURLResponse?>

这意味着您可以将可选 NSURLResponse的地址作为参数传递：

var response : NSURLResponse?
NSURLConnection.sendSynchronousRequest(request, returningResponse: &response , error: nil)

然后，您可以有条件地将返回的回复转换为NSHTTPURLResponse：

if let httpResponse = response as? NSHTTPURLResponse {
    println(httpResponse.expectedContentLength)
}

请注意，您应该检查sendSynchronousRequest()的返回值如果无法建立联系，则为nil。

还建议拨打此电话方法只来自一个单独的线程（或使用sendAsynchronousRequest()代替）因为建立连接可能需要一段时间 - 特别是在使用蜂窝网络时 - 主线程将是否则阻止。

Answer 2

Swift 4解决方案：

func fetchContentLength(for url: URL, completionHandler: @escaping (_ contentLength: Int64?) -> ()) {

    var request = URLRequest(url: url)
    request.httpMethod = "HEAD"

    let task = URLSession.shared.dataTask(with: request) { (data, response, error) in
    guard error == nil, let response = response as? HTTPURLResponse, let contentLength = response.allHeaderFields["Content-Length"] as? String else {
        completionHandler(nil)
        return
    }
        completionHandler(Int64(contentLength))
    }

        task.resume()
}

// Usage:

let url = URL(string: "https://s3.amazonaws.com/x265.org/video/Tears_400_x265.mp4")!

fetchContentLength(for: url, completionHandler: { contentLength in
    print(contentLength ?? 0)
})

使用NSURLConnection的URL文件大小 - Swift

2 个答案: