<HTTP>HttpDownload的实现（ASIHTTP和NSConnection两种方式）

ASIHTTPRequest是第三方包，使用前需要导入的包：MobileCoreServices、SystemConfiguration、CFNetwork、libz。

这里写的HttpDownload类可以实现用参数选择两种方式中一种来实现HTTP下载。并且通过callMethod函数实现回调。

下面是HttpDownload.h

#import <Foundation/Foundation.h>
#import "ASIHTTPRequest.h"
#define DOWNLOAD_SYSTEM 1
#define DOWNLOAD_ASIHTTPREQUEST 2

@interface HttpDownload : NSObject<ASIHTTPRequestDelegate,NSURLConnectionDataDelegate>
{
    //回调的方法
    SEL callMethod;
    //代理
    id delegate;
    NSURLConnection *mConnection;
    NSInteger mType;
    //用于存放下载到的二进制数据
    NSMutableData *mData;
}
@property (nonatomic,retain) NSMutableData *mData;

-(void)downloadFromUrl:(NSString *)url delegate:(id)delegate selector:(SEL)selector type:(NSInteger)type;

@end

下面是HttpDownload.m

#import "HttpDownload.h"
@implementation HttpDownload
@synthesize mData;
//在初始化函数中为mData分配空间
-(id)init
{
    if (self=[super init]) {
        mData=[[NSMutableData alloc] init];
    }
    return self;
}
//dealloc时对mData进行内存回收
-(void)dealloc
{
    self.mData=nil;
    [super dealloc];
}
//参数一表示下载地址，参数二表示回调对象地址，参数3表示回调函数地址，参数四是下载类型
-(void)downloadFromUrl:(NSString *)url delegate:(id)newdelegate selector:(SEL)selector type:(NSInteger)type
{
    delegate=newdelegate;
    callMethod=selector;
    //关于类型的宏定义
    // #define DOWNLOAD_SYSTEM 1
    // #define DOWNLOAD_ASIHTTPREQUEST 2
    if (type==DOWNLOAD_ASIHTTPREQUEST) {
        ASIHTTPRequest *request=[ASIHTTPRequest requestWithURL:[NSURL URLWithString:url]];
        request.delegate=self;
        //启动异步下载
        [request startAsynchronous];
        //后面继续执行requestfinish或者requestFail方法
    }
    else if(type==DOWNLOAD_SYSTEM){
        if (mConnection) {
            [mConnection cancel];
            [mConnection release];
        }
        mConnection=[[NSURLConnection alloc] initWithRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:url]] delegate:self];
        //后面执行connection:系列函数
    }
    else{
        NSLog(@"暂没实现");
    }
}
//得到回应，即将开始开始接收数据时
-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    //清空mData
    [mData setLength:0];
}
//得到数据时
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    //将数据存到mData
    [mData appendData:data];
}

-(void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    //检查代理是否可用以及是否实现方法callMethod
    if(delegate && [delegate respondsToSelector:callMethod]){
        //调用对象delegate的方法callMethod传的参数为self
        [delegate performSelector:callMethod withObject:self];
        //下面这个不能用，因为成员变量delegate是id类型的。
        //[delegate callMethod:self];
    }
}
-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    NSLog(@"系统下载失败");

}
-(void)requestFinished:(ASIHTTPRequest *)request
{
    [mData setLength:0];
    [mData appendData:[request responseData]];
    //检查代理是否可用以及是否实现方法callMethod
    if(delegate && [delegate respondsToSelector:callMethod]){
        //调用对象delegate的方法callMethod传的参数为self
        [delegate performSelector:callMethod withObject:self];
        //[delegate callMethod:self];
    }
}
-(void)requestFailed:(ASIHTTPRequest *)request
{
    NSLog(@"第三方下载失败");
}
@end