我试图下载前得到URL的文件大小
这里是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];
这里是银行代码
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)
但我有错误这里
NSURLConnection.sendSynchronousRequest(request, returningResponse: &response , error: nil)
'NSHTTPURLResponse' is not identical to 'NSURLResponse?'
我错过在这里迅速什么?
响应参数有类型
AutoreleasingUnsafeMutablePointer<NSURLResponse?>
这意味着你可以通过一个可选的地址NSURLResponse
作为参数:
var response : NSURLResponse?
NSURLConnection.sendSynchronousRequest(request, returningResponse: &response , error: nil)
然后,您可以有条件地转换为返回的响应NSHTTPURLResponse
:
if let httpResponse = response as? NSHTTPURLResponse {
println(httpResponse.expectedContentLength)
}
请注意,您应该检查返回值sendSynchronousRequest()
这是nil
,如果没有连接可以作出。
此外,还建议调用仅从一个单独的线程此方法(或使用sendAsynchronousRequest()
代替),因为它可能需要一段时间来建立连接-使用蜂窝网络时特别-和主线程否则会被阻塞。
斯威夫特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)
})