iOS 检测新版本

-(void)checkAppUpdate
{
    NSDictionary *infoDict = [[NSBundle mainBundle] infoDictionary];
    
    NSString *nowVersion = [infoDict objectForKey:@"CFBundleVersion"];
    
    NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"http://itunes.apple.com/lookup?id=%@", JWversionNumber]];
    NSString * file =  [NSString stringWithContentsOfURL:url encoding:NSUTF8StringEncoding error:nil];
    
    NSRange substr = [file rangeOfString:@"\"version\":\""];//判断是不是找到字符
    NSRange range1 = NSMakeRange(substr.location+substr.length,10);
    NSRange substr2 =[file rangeOfString:@"\"" options:nil range:range1];
    NSRange range2 = NSMakeRange(substr.location+substr.length, substr2.location-substr.location-substr.length);
    NSString *newVersion =[file substringWithRange:range2];
    if(![nowVersion isEqualToString:newVersion] && newVersion !=nil)
    {
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:nil message:@"版本有更新"delegate:self cancelButtonTitle:@"取消"otherButtonTitles:@"更新",nil];
        alert.tag = 222;
        [alert show];
    }else{
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:nil message:@"已经是最新版本"delegate:self cancelButtonTitle:@"确定"otherButtonTitles:nil,nil];
        alert.tag = 222;
        [alert show];
    }
}