直接上代码：

/**
 *  检测软件是否需要升级
 */
-(void)checkVersion
{
    NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"http://itunes.apple.com/cn/lookup?id=%i",iFeverAPPID]];
    ASIHTTPRequest *request = [[ASIHTTPRequest alloc]initWithURL:url];
    [request setUseCookiePersistence:YES];
    [request setDelegate: self];
    [request setDidFailSelector:@selector(getVersionRequestFailed:)];
    [request setDidFinishSelector:@selector(getVersionRequestSuccess:)];
    [request startAsynchronous];//开始异步请求
}

-(void)getVersionRequestFailed:(ASIHTTPRequest *)request1
{
    NSLog(@"从AppStore获取版本信息失败！！");
}

-(void)getVersionRequestSuccess:(ASIHTTPRequest *)request1
{
    NSString *newVersion;
    NSData *responseData = [request1 responseData];
    NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:responseData options:NSJSONReadingAllowFragments error:nil];
    NSArray *resultArray = [dic objectForKey:@"results"];
    for (id config in resultArray) {
        newVersion = [config valueForKey:@"version"];
    }
    if (newVersion) {
        NSLog(@"通过AppStore获取的版本号是：%@",newVersion);
    }
    //获取本地版本号
    NSString *localVersion = [[[NSBundle mainBundle]infoDictionary]objectForKey:@"CFBundleVersion"];
    NSString *msg = [NSString stringWithFormat:@"你当前的版本是V%@，发现新版本V%@，是否下载新版本？",localVersion,newVersion];
    if ([newVersion floatValue] > [localVersion floatValue]) {
        UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"升级提示!" message:msg delegate:self cancelButtonTitle:@"下次再说" otherButtonTitles:@"现在升级", nil];
        alert.tag = kVersionNeedUpdateAlertTag;
        [alert show];
    }
}

-(void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
    if (alertView.tag == kVersionNeedUpdateAlertTag) {
        //软件需要更新提醒
        if (buttonIndex == 1) {
            NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"https://itunes.apple.com/cn/app/wan-zhuan-quan-cheng/id%i?mt=8",iFeverAPPID]];
            [[UIApplication sharedApplication]openURL:url];
            /*
             // 打开iTunes 方法二:此方法总是提示“无法连接到itunes”，不推荐使用
             NSString *iTunesLink = @"itms-apps://phobos.apple.com/WebObjects/MZStore.woa/wa/viewSoftwareUpdate?id=%i&mt=8";
             NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"itms-apps://phobos.apple.com/WebObjects/MZStore.woa/wa/viewSoftwareUpdate?id=%i&mt=8",iFeverAPPID]];
             [[UIApplication sharedApplication] openURL:url];
             */
        }
    }
}

如果想知道网络请求AppStore时返回的信息可以打开这个链接：http://itunes.apple.com/cn/lookup?id=465039730

参考博文：

iOS appStore中的应用 实现升级功能http://www.cnblogs.com/ygm900/p/3334586.html

//基于企业级证书的IOS应用打包升级功能介绍

http://blog.csdn.net/sbvfhp/article/details/10336715

//另一种代码实现思路

http://hi.baidu.com/wwssttt/item/7446105e3c98fa3933e0a9d5

//向appStore获取软件版本的代码，有步骤

http://blog.csdn.net/wave_1102/article/details/7463697

//向 appstore 查询已发布 APP 的信息--纯思路

http://hi.baidu.com/yanh105/item/7378a98ffca6a8804414cfa0

//官方帮助文档

http://www.apple.com/itunes/affiliates/resources/documentation/itunes-store-web-service-search-api.html

//如何改进iOS客户端的升级提醒功能

http://www.cocoachina.com/applenews/devnews/2013/0108/5495.html

//ios项目如何实现版本更新？

http://blog.csdn.net/mad1989/article/details/8130013

//解决向appStore 发送请求获取版本，没有返回信息的问题

http://www.cocoachina.com/ask/questions/show/56158