点击链接直接跳转到 App Store 指定应用下载页面

//跳转到应用页面
NSString *str = [NSString stringWithFormat:@"http://itunes.apple.com/us/app/id%d",appid];
[[UIApplication sharedApplication] openURL:[NSURL urlWithString:str]]; 

//跳转到评价页面
NSString *str = [NSString stringWithFormat: @"itms-apps://ax.itunes.apple.com/WebObjects/MZStore.woa/wa/viewContentsUserReviews?type=Purple+Software&id;=%d",
                         appid ];
[[UIApplication sharedApplication] openURL:[NSURL urlWithString:str]];