在.h 文件中  实现NSURLConnectionDataDelegate协议

@property (nonatomic, assign) IBOutlet UIProgressView *progressView;

– (IBAction)download;

{
    // 文件的总长度
    int _totalLength;
}
@property (nonatomic, retain) NSMutableData *data;

.m 文件中

– (void)dealloc {
    [_data release];
    [super dealloc];
}

– (void)viewDidUnload {
    [super viewDidUnload];
    self.data = nil;
}

– (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    
}

– (void)download {
    
    self.data = [NSMutableData data];
    
    NSURL *url = [NSURL URLWithString:@”http://192.168.1.106:8080/MJServer/movie.avi”];
    
    NSURLRequest *reuqest = [NSURLRequest requestWithURL:url];
    
    [[NSURLConnection connectionWithRequest:reuqest delegate:self] start];
}

#pragma mark – 代理方法
– (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    [self.data appendData:data];
    
    // 设置下载进度
    self.progressView.progress = (float)self.data.length / (float)_totalLength;
}

#pragma mark 服务器有相应就会调用这个方法
– (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    NSHTTPURLResponse *rep = (NSHTTPURLResponse *)response;
    
    _totalLength = [[[rep allHeaderFields] objectForKey:@”Content-Length”] intValue];
}

//下载完成后放到指定的文件夹中
– (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    NSString *cacheDir = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
    
    NSString *dir = [cacheDir stringByAppendingPathComponent:@”movie”];
    
    NSFileManager *mgr = [NSFileManager defaultManager];
    
    // 是否为文件夹
    BOOL isDir;
    // 是否存在
    BOOL exist = [mgr fileExistsAtPath:dir isDirectory:&isDir];
    if (!exist) {
        // 创建一个新的文件夹
        [mgr createDirectoryAtPath:dir withIntermediateDirectories:YES attributes:nil error:nil];
    }
    
    NSString *path = [dir stringByAppendingPathComponent:@”mj.avi”];
    // 将文件数据写入Library/Caches文件夹下
    [self.data writeToFile:path atomically:YES];
}