iOS9 alert问题

iOS9之后alertview不让用啦，用UIAlertController吧

UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"警告" message:@"xxxxxxx" preferredStyle:UIAlertControllerStyleAlert];

[alert addAction:[UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {

}]];
[alert addAction:[UIAlertAction actionWithTitle:@"取消" style:UIAlertActionStyleCancel handler:^(UIAlertAction *action) {

}]];
[self presentViewController:alert animated:YES completion:^{
// dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
// [self dismissViewControllerAnimated:YES completion:nil];
// });
}];