创建一个写入流写入一个文件到程序的临时目录里

先获得写入的路径：

self.filePath = [[NetworkManager sharedInstance] pathForTemporaryFileWithPrefix:@"Get"];

- (NSString *)pathForTemporaryFileWithPrefix:(NSString *)prefix
{
NSString *  result;
CFUUIDRef   uuid;
CFStringRef uuidStr;

uuid = CFUUIDCreate(NULL);
assert(uuid != NULL);

uuidStr = CFUUIDCreateString(NULL, uuid);
assert(uuidStr != NULL);

result = [NSTemporaryDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:@"%@-%@", prefix, uuidStr]];
assert(result != nil);

CFRelease(uuidStr);
CFRelease(uuid);

return result;
}

创建写入流，并打开流

assert(self.filePath != nil);

self.fileStream = [NSOutputStream outputStreamToFileAtPath:self.filePath append:NO];
assert(self.fileStream != nil);

[self.fileStream open];

发送url请求

request = [NSURLRequest requestWithURL:url];
assert(request != nil);

self.connection = [NSURLConnection connectionWithRequest:request delegate:self];
assert(self.connection != nil);

实现代理方法，将文件写入到临时目录

- (void)connection:(NSURLConnection *)theConnection didReceiveData:(NSData *)data
{
#pragma unused(theConnection)
NSInteger       dataLength;
const uint8_t * dataBytes;
NSInteger       bytesWritten;
NSInteger       bytesWrittenSoFar;

assert(theConnection == self.connection);

dataLength = [data length];
dataBytes  = [data bytes];

bytesWrittenSoFar = 0;
do {
bytesWritten = [self.fileStream write:&dataBytes[bytesWrittenSoFar] maxLength:dataLength - bytesWrittenSoFar];
assert(bytesWritten != 0);
if (bytesWritten == -1) {
[self stopReceiveWithStatus:@"File write error"];
break;
} else {
bytesWrittenSoFar += bytesWritten;
}
} while (bytesWrittenSoFar != dataLength);
}

还有写代理方法也要去实现，例如：

- (void)connectionDidFinishLoading:(NSURLConnection *)theConnection

- (void)connection:(NSURLConnection *)theConnection didFailWithError:(NSError *)error

- (void)connection:(NSURLConnection *)theConnection didReceiveResponse:(NSURLResponse *)response