iOS网络下载（一）三函数

原生的NSURL同步下载，并且调用三个函数
  RootViewController.h中定义
  NSURLConnection * myConnection;//连接网络
    NSMutableData * allData;//存储网络下载的数据
  
其中：
- (void)viewDidLoad
{
    [superviewDidLoad];
    NSString * urlString=@"http://www.baidu.com/img/baidu_jgylogo3.gif";
    NSURL * url = [NSURLURLWithString:urlString];
    NSURLRequest * request = [[NSURLRequest alloc] initWithURL:url];//通过url，获得request;
    myConnection = [[NSURLConnection alloc] initWithRequest:request delegate:self];//根据request得到connection;
    [request release];
}
网络三个函数
- (void)connectionDidFinishLoading:(NSURLConnection *)connection//下载完成,可以对一些数据进行处理，如在这里就用data得到图片；
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    [myConnection release];
    
    NSString * string = [[NSStringalloc] initWithData:allDataencoding:NSUTF8StringEncoding];
    NSLog(@"string ------------------- > %@",string);
    NSLog(@"functiono %s is calling",__func__);//获得方法名称
    UIImage * img = [UIImageimageWithData:allData];
    CGRect imageframe = CGRectMake(0, 0, img.size.width, img.size.height);
    UIImageView * imageview = [[UIImageViewalloc] initWithFrame:imageframe];
    [imageview setImage:img];
    [self.viewaddSubview:imageview];
    [imageview release];
    [string release];
    [allDatarelease]; 
｝
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{     //每接收一段数据就会调用此函数
    [allDataappendData:data];//把data加到allData最后
}
//接收完HTTP协议头，开始真正接手数据时候调用
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    allData = [[NSMutableDataalloc] initWithLength:0];
   // NSLog(@"functiono %s is calling",__func__);
    NSHTTPURLResponse * res = (NSHTTPURLResponse *)response;
    NSInteger statusCode = [res statusCode];
    if(statusCode >= 400)
    {
        NSLog(@"HTTP ERROR CODE %d",statusCode);
    }
    NSDictionary * dic = [res allHeaderFields];
    NSLog(@"all Header Field %@",dic);
}