iOS下载大文件原理解析一

iOS中下载大型文件，需要考虑到占用内存的大小与下载速度（使用多线程），因此本文首先介绍一个原理性下载文件的DEMO。
在下载大型文件中，需要知道下载的进度因此需要使用代理模式，不断的回调下载进度。
- (void)downLoad {
// 1.URL
NSURL *url = [NSURL URLWithString:@”http://localhost:8080/MJServer/resources/videos.zip“];
// 2.NURLRequest
NSURLRequest *request = [NSURLRequest requestWithURL:url];
// 3.开始创建TCP连接
[NSURLConnection connectionWithRequest:request delegate:self];
// [[NSURLConnection alloc]initWithRequest:request delegate:self];
// NSURLConnection *connection = [[NSURLConnection alloc]initWithRequest:request delegate:self startImmediately:NO];
// [connection start];
}

下面是代理方法：
- (void)connection:(NSURLConnection )connection didFailWithError:(NSError )error {
NSLog(@”didFailWithError”);
}
- (void)connection:(NSURLConnection )connection didReceiveResponse:(NSURLResponse )response {
self.fileData = [NSMutableData data];
// NSHTTPURLResponse * resp = (NSHTTPURLResponse*)response;
// long long fileLength = [resp.allHeaderFields[@”Content-Length”]longLongValue];
self.totalLength = response.expectedContentLength;
}
- (void)connection:(NSURLConnection )connection didReceiveData:(NSData )data {
[self.fileData appendData:data];
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
NSString *caches = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
NSString *file = [caches stringByAppendingPathComponent:@”videos.zip”];
[self.fileData writeToFile:file atomically:YES];
}