转自：http://blog.csdn.net/xyz_lmn/article/details/8968182
移动互联网时代，网络通信已是手机终端必不可少的功能。我们的应用中也必不可少的使用了网络通信，增强客户端与服务器交互。这一篇提供了使用NSURLConnection实现http通信的方式。
NSURLConnection提供了异步请求、同步请求两种通信方式。
1、异步请求
iOS5.0 SDK NSURLConnection类新增的sendAsynchronousRequest:queue:completionHandler:方法，从而使iOS5支持两种异步请求方式。我们先从新增类开始。
1）sendAsynchronousRequest
iOS5.0开始支持sendAsynchronousReques方法，方法使用如下：
- - (void)httpAsynchronousRequest{
- NSURL *url = [NSURL URLWithString:@"http://url"];
- NSString *post=@"postData";
- NSData *postData = [post dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];
- NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
- [request setHTTPMethod:@"POST"];
- [request setHTTPBody:postData];
- [request setTimeoutInterval:10.0];
- NSOperationQueue *queue = [[NSOperationQueue alloc]init];
- [NSURLConnection sendAsynchronousRequest:request
- queue:queue
- completionHandler:^(NSURLResponse *response, NSData *data, NSError *error){
- if (error) {
- NSLog(@"Httperror:%@%d", error.localizedDescription,error.code);
- }else{
- NSInteger responseCode = [(NSHTTPURLResponse *)response statusCode];
- NSString *responseString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
- NSLog(@"HttpResponseCode:%d", responseCode);
- NSLog(@"HttpResponseBody %@",responseString);
- }
- }];
- }
sendAsynchronousReques可以很容易地使用NSURLRequest接收回调，完成http通信。
2）connectionWithRequest
iOS2.0就开始支持connectionWithRequest方法，使用如下：
- - (void)httpConnectionWithRequest{
- NSString *URLPath = [NSString stringWithFormat:@"http://url"];
- NSURL *URL = [NSURL URLWithString:URLPath];
- NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:URL];
- [NSURLConnection connectionWithRequest:request delegate:self];
- }
- - (void)connection:(NSURLConnection *)theConnection didReceiveResponse:(NSURLResponse *)response
- {
- NSInteger responseCode = [(NSHTTPURLResponse *)response statusCode];
- NSLog(@"response length=%lld statecode%d", [response expectedContentLength],responseCode);
- }
- // A delegate method called by the NSURLConnection as data arrives. The
- // response data for a POST is only for useful for debugging purposes,
- // so we just drop it on the floor.
- - (void)connection:(NSURLConnection *)theConnection didReceiveData:(NSData *)data
- {
- if (mData == nil) {
- mData = [[NSMutableData alloc] initWithData:data];
- } else {
- [mData appendData:data];
- }
- NSLog(@"response connection");
- }
- // A delegate method called by the NSURLConnection if the connection fails.
- // We shut down the connection and display the failure. Production quality code
- // would either display or log the actual error.
- - (void)connection:(NSURLConnection *)theConnection didFailWithError:(NSError *)error
- {
- NSLog(@"response error%@", [error localizedFailureReason]);
- }
- // A delegate method called by the NSURLConnection when the connection has been
- // done successfully. We shut down the connection with a nil status, which
- // causes the image to be displayed.
- - (void)connectionDidFinishLoading:(NSURLConnection *)theConnection
- {
- NSString *responseString = [[NSString alloc] initWithData:mData encoding:NSUTF8StringEncoding];
- NSLog(@"response body%@", responseString);
- }
connectionWithRequest需要delegate参数，通过一个delegate来做数据的下载以及Request的接受以及连接状态，此处delegate:self，所以需要本类实现一些方法，并且定义mData做数据的接受。
需要实现的方法：
1、获取返回状态、包头信息。
- - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response;
2、连接失败，包含失败。
- - (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error;
3、接收数据
- - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data;
4、数据接收完毕
- (void)connectionDidFinishLoading:(NSURLConnection *)connection;
connectionWithRequest使用起来比较繁琐，而iOS5.0之前用不支持sendAsynchronousRequest。有网友提出了AEURLConnection解决方案。
- AEURLConnection is a simple reimplementation of the API for use on iOS 4. Used properly, it is also guaranteed to be safe against The Deallocation Problem, a thorny threading issue that affects most other networking libraries.
2、同步请求
同步请求数据方法如下：
- - (void)httpSynchronousRequest{
- NSURLRequest * urlRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://google.com"]];
- NSURLResponse * response = nil;
- NSError * error = nil;
- NSData * data = [NSURLConnection sendSynchronousRequest:urlRequest
- returningResponse:&response
- error:&error];
- if (error == nil)
- {
- // 处理数据
- }
- }
同步请求数据会造成主线程阻塞，通常在请求大数据或网络不畅时不建议使用。
从上面的代码可以看出，不管同步请求还是异步请求，建立通信的步骤基本是一样的：
1、创建NSURL
2、创建Request对象
3、创建NSURLConnection连接。
NSURLConnection创建成功后，就创建了一个http连接。异步请求和同步请求的区别是：创建了异步请求，用户可以做其他的操作，请求会在另一个线程执行，通信结果及过程会在回调函数中执行。同步请求则不同，需要请求结束用户才能做其他的操作。