获取app的下载链接

http://www.jianshu.com/p/db785c3f1603

拿到app id

NSString *iTunesString = [NSString stringWithFormat:@"http://itunes.apple.com/app/id%@", appid];    
  NSURL *iTunesURL = [NSURL URLWithString:iTunesString];        
[[UIApplication sharedApplication] openURL:iTunesURL];