【iOS開發-網絡】大文件的斷點續傳(斷點下載)

要想實現斷點續傳，暫停的時候要取消connection連接，
開始下載的時候要給服務器發送頭信息，告訴他要請求多長的數據，從哪裏開始

//暫停
    if(sender.selected) {

        [self.conn cancel];//取消連接
        self.conn = nil;

//開始        
    } else {

        //創建url
        NSURL *url = [NSURL URLWithString:@"http://localhost:8080/TFServer/resources/videos/minion_01.mp4"];

        //創建請求 這裏不是NSURLRequest
        NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];

        //創建頭信息
        NSString *range = [NSString stringWithFormat:@"bytes=%lld-", self.fileLength];

        //設置頭信息
        [request setValue:range forHTTPHeaderField:@"Range"];

        //發出一個異步請求
        self.conn = [NSURLConnection connectionWithRequest:request delegate:self];
    }