这里对网络请求方式做一个总结。
原生方式同步GET请求：
NSString *urlStr = @"http://apis.juhe.cn/mobile/get?phone=13429667914&key=e87a054855796995c9e2b48e8514d0da";
urlStr = [urlStr stringByAddingPercentEscapesUsingEncoding: NSUTF8StringEncoding];
NSURL *url = [NSURL URLWithString:urlStr];
NSURLRequest *request = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:];
NSURLResponse *response = nil;
NSError *error = nil;
NSData *responseData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];
NSString *responseString = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding];
NSLog(@"%@", responseString);
原生方式异步GET请求：
NSString *urlStr = @"http://apis.juhe.cn/mobile/get?phone=13429667914&key=e87a054855796995c9e2b48e8514d0da";
urlStr = [urlStr stringByAddingPercentEscapesUsingEncoding: NSUTF8StringEncoding];
NSURL *url = [NSURL URLWithString:urlStr];
NSURLRequest *request = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:];
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
NSString *responseString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
NSLog(@"%@", responseString);
}];
可见，请求分为两部分，一是构建请求，二是发送请求。构建分为GET和POST，发送分为同步和异步。
POST请求的请求部分需要将参数构建为NSData类型：
NSString *urlStr = @"http://apis.juhe.cn/mobile/get?";
urlStr = [urlStr stringByAddingPercentEscapesUsingEncoding: NSUTF8StringEncoding];
NSURL *url = [NSURL URLWithString:urlStr];
//创建请求，配置参数的data
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:];
[request setHTTPMethod:@"POST"];
NSString *otherURLstr = @"phone=13429667914&key=e87a054855796995c9e2b48e8514d0da";
NSData *otherURLData = [otherURLstr dataUsingEncoding:NSUTF8StringEncoding];
[request setHTTPBody:otherURLData];
原生方式写出来的代码总是一坨，下面看看AFN对请求的封装。AFN需要添加MobileCoreService和SystemConfiguration框架，并在pch里加入头文件：
#import <MobileCoreServices/MobileCoreServices.h>
#import <SystemConfiguration/SystemConfiguration.h>
在使用时需要引入头文件：
#import "AFNetworking.h"
GET和POST的请求的构建还是和前面一样，发送处：
AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
NSLog(@"%@", operation.responseString);
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
NSLog(@"%@", [error localizedDescription]);
}];
[operation start];
AFHTTPRequestOperation是操作队列的子类，显然AFN的请求是异步的（当然，既然是操作队列，就可以用操作队列的方法控制它），请求完成后触发回调。
AFN支持自动解析JSON并转化为词典结构：
AFJSONRequestOperation *operation = [AFJSONRequestOperation JSONRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {
NSLog(@"%@", JSON);
} failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id JSON) {
}];
[operation start];
但是个人不建议使用它解析XML，因为它采用的是XMLParser的方式，很繁琐。
但是这还是显得一坨一坨的，于是有两种办法，第一种就是再封装一层简单的API，就像jQueryAjax一样，第二种就是每次用的时候复制粘贴啦~
使用AFN也可以很方便地实现文件异步下载：
//目标地址
NSURL *url = [NSURL URLWithString:@"http://www.baidu.com/img/baidu_sylogo1.gif"];
NSURLRequest *request = [NSURLRequest requestWithURL:url]; //构建AFN操作
AFURLConnectionOperation *operation = [[AFHTTPRequestOperation alloc]initWithRequest:request]; //设置输出流
NSArray *documents = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
NSString *downloadPath = [documents[] stringByAppendingPathComponent:@"1.gif"];
[operation setOutputStream:[NSOutputStream outputStreamToFileAtPath:downloadPath append:NO]]; //下载过程当中的block（检测进度）
[operation setDownloadProgressBlock:^(NSUInteger bytesRead, long long totalBytesRead, long long totalBytesExpectedToRead) {
NSLog(@"下载百分比：%f", (float)totalBytesRead / totalBytesExpectedToRead);
}]; //下载完成
[operation setCompletionBlock:^{
NSLog(@"操作完成");
}];