iOS NSURLConnection 同步异步GET、POST请求

NSURLConnection GET&POST

1、同步GET请求
NSURL *url = [NSURL URLWithString:@"http://api.hudong.com/iphonexml.do?type=focus-c"]; NSURLRequest *request = [[NSURLRequest alloc]initWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10];
      其中缓存协议是个枚举类型包含：
      NSURLRequestUseProtocolCachePolicy（基础策略）
      NSURLRequestReloadIgnoringLocalCacheData（忽略本地缓存）
      NSURLRequestReturnCacheDataElseLoad（首先使用缓存，如果没有本地缓存，才从原地址下载）
      NSURLRequestReturnCacheDataDontLoad（使用本地缓存，从不下载，如果本地没有缓存，则请求失败，此策略多用于离线操作）
      NSURLRequestReloadIgnoringLocalAndRemoteCacheData（无视任何缓存策略，无论是本地的还是远程的，总是从原地址重新下载）
      NSURLRequestReloadRevalidatingCacheData（如果本地缓存是有效的则不下载，其他任何情况都从原地址重新下载）
    
NSData *received = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
NSString *str = [[NSString alloc]initWithData:received encoding:NSUTF8StringEncoding];
NSLog(@"%@",str);

2、同步POST请求
NSURL *url = [NSURL URLWithString:@"http://api.hudong.com/iphonexml.do"];
NSMutableURLRequest *request = [[NSMutableURLRequest alloc]initWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10];
[request setHTTPMethod:@"POST"];//设置请求方式为POST，默认为GET
NSString *str = @"type=focus-c";//设置参数
NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding];
[request setHTTPBody:data];
NSData *received = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
NSString *str1 = [[NSString alloc]initWithData:received encoding:NSUTF8StringEncoding];
NSLog(@"%@",str1);

3、异步GET请求
    //第一步，创建url
    NSURL *url = [NSURL URLWithString:@"http://api.hudong.com/iphonexml.do?type=focus-c"];
    //第二步，创建请求
    NSURLRequest *request = [[NSURLRequest alloc]initWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10];
    //第三步，连接服务器
    NSURLConnection *connection = [[NSURLConnection alloc]initWithRequest:request delegate:self];

4、异步POST请求
    //第一步，创建url
    NSURL *url = [NSURL URLWithString:@"http://api.hudong.com/iphonexml.do"];
    //第二步，创建请求
    NSMutableURLRequest *request = [[NSMutableURLRequest alloc]initWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10];
    [request setHTTPMethod:@"POST"];
    NSString *str = @"type=focus-c";
    NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding];
    [request setHTTPBody:data];
    //第三步，连接服务器
    NSURLConnection *connection = [[NSURLConnection alloc]initWithRequest:request delegate:self];