1 @interface ViewController ()<NSURLConnectionDataDelegate>
 2 {
 3     // 文件的总大小
 4     long long _total;
 5     // 当前下载
 6     long long _current;
 7 }
 8 
 9 // 文件句柄
10 @PRoperty (nonatomic,strong)NSFileHandle *fileHandle;
11 // 连接对象
12 @property (nonatomic,strong)NSURLConnection *conn;
13 @property (weak, nonatomic) IBOutlet UiprogressView *progress;
14 @property (weak, nonatomic) IBOutlet UIButton *button;
15 @end
16 
17 @implementation ViewController
18 - (void)viewDidLoad {
19     [super viewDidLoad];
20     self.progress.progress = 0;
21     // Do any additional setup after loading the view, typically from a nib.
22 }
23 
24 - (IBAction)buttonAction:(UIButton *)sender {
25     if ([[sender titleForState:UIControlStateNormal]isEqualToString:@"开始"]) {
26         [sender setTitle:@"暂停" forState:(UIControlStateNormal)];
27         // 请求
28         NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:kUrl]];
29         // 设置请求参数
30         NSString *rang = [NSString stringWithFormat:@"byte:%lld",_current];
31         NSLog(@"request:%@end",request);
32         [request setValue:rang forHTTPHeaderField:@"Range"];
33          NSLog(@"request:%@end",request);
34         // 建立连接
35         self.conn = [NSURLConnection connectionWithRequest:request delegate:self];
36         // 开始请求
37         [_conn start];
38     }else{
39         [sender setTitle:@"开始" forState:(UIControlStateNormal)];
40         // 取消
41         [_conn cancel];
42     }
43 }
44 
45 - (void)didReceiveMemoryWarning {
46     [super didReceiveMemoryWarning];
47     // Dispose of any resources that can be recreated.
48 }
49 
50 #pragma mark---delegate
51 // 收到响应
52 - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
53 {
54     // 获取总文件大小(总文件的大小在响应里面可以获得)
55     _total = response.expectedContentLength;
56     // 创建文件
57     NSFileManager *manager = [NSFileManager defaultManager];
58     NSString *cachesPath  = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES)[0];
59     NSString *filePath = [cachesPath stringByAppendingPathComponent:@"music.mp3"];
60     NSLog(@"%@",cachesPath);
61     // 创建文件
62     [manager createFileAtPath:filePath contents:nil attributes:nil];
63     // 让文件句柄指向文件
64     self.fileHandle = [NSFileHandle fileHandleForWritingAtPath:filePath];
65 }
66 // 接收到数据
67 - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
68 {
69     // 计算当前总大小
70     _current += data.length;
71     // 更新 （在子线程中不能更新UI）
72     [self performSelectorOnMainThread:@selector(updateProgress) withObject:self waitUntilDone:YES];
73     // 指向文件末尾
74     [self.fileHandle seekToEndOfFile];
75     // 写数据
76     [self.fileHandle writeData:data];
77 }
78 // 结束
79 - (void)connectionDidFinishLoading:(NSURLConnection *)connection
80 {
81     NSLog(@"下载完毕");
82 }
83 // 更新progress
84 - (void)updateProgress
85 {
86     self.progress.progress = (long double)_current / (long double)_total;
87 }
88 
89 @end