网络请求的步骤：

GET 、POST

GET暴露太多，很少用

1.NSURL;

2.NSURLRequest

3.NSURLConnection

4.处理Error or 返回数据

example：

//1.获取 urlstring
    NSString * urlString = [NSString stringWithFormat:@"%@",GETurl];
    
    //采用utf-8编码
    urlString = [urlString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
    //2.
    NSURL * url = [NSURL URLWithString:urlString];
    //3.请求数据
    //    
    NSURLRequest * request = [NSURLRequest requestWithURL:url];
    
    [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue]completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
        self.imageView11.image = [UIImage imageWithData:data];
    }];