how can I present a UIAlertController above UIViewController.view.window - ios8

Question

Now, I created a UIViewController called viewController, and add a subview called maskView on viewController via:
UIView *maskView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, SCREEN_SIZE.width, SCREEN_SIZE.height)];
[self.view.window addSubview:maskView];
and then on maskView there is a button called "deleteBtn", when click on the deleteBtn, I want to present a UIAlertController via:
UIAlertController *alertController = [UIAlertController alertControllerWithTitle:NSLocalizedString(#"mybulb.confirmRemove", #"") message:#"" preferredStyle:UIAlertControllerStyleAlert];
UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:NSLocalizedString(#"cancel", #"取消") style:UIAlertActionStyleDefault handler:nil];
UIAlertAction *confirmAction = [UIAlertAction actionWithTitle:NSLocalizedString(#"confirm", #"确定") style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
}];
[alertController addAction:cancelAction];
[alertController addAction:confirmAction];
[self presentViewController:alertController animated:YES completion:nil];
but the alertController is not present on the topmost screen, it is below the maskView, how can I show the alertController above the maskView added on UIViewController.view.window?
Thanks so much!

Answer 1

finally I fixed this problem by creating a new window object and switch between this window and the default one, the code like this:
if ([UIAlertController class]) {
AppDelegate *appDelegate = [UIApplication sharedApplication].delegate;
UIAlertController *alertController = [UIAlertController alertControllerWithTitle:NSLocalizedString(#"readus.org.title", #"alert title") message:#"" preferredStyle:UIAlertControllerStyleAlert];
UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:NSLocalizedString(#"readus.org.cancel", #"取消") style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
[appDelegate.window makeKeyAndVisible];
}];
UIAlertAction *confirmAction = [UIAlertAction actionWithTitle:NSLocalizedString(#"readus.org.confirm", #"确定") style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
//do anything you like...
[appDelegate.window makeKeyAndVisible];
}];
[alertController addAction:cancelAction];
[alertController addAction:confirmAction];
[self.alertWindow makeKeyAndVisible];
[self.alertWindow.rootViewController presentViewController:alertController animated:YES completion:nil];
}
and self.alertWindow is defined as:
#property (strong, nonatomic) UIWindow *alertWindow;
- (UIWindow *)alertWindow {
if (!_alertWindow) {
_alertWindow = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
UIViewController *viewController = [[UIViewController alloc] init];
_alertWindow.rootViewController = viewController;
}
return _alertWindow;
}