How do I put a UIActivityIndicatorView in a UIAler

We're moving away from MBProgressHUD because it's too glitchy in our app, and doesn't have features such as blocking user input or providing a Cancel button.

So, I've attempted to implement Swipesight's How to display activity indicator in center of UIAlertController?, and I ran into improper positioning of the indicator:

^{It is green because our app's tint is green.}

As you can see, it's not in the white rectangle part of the controller, but the grey background. This uses something similar to his "@62Shark" solution:

// in implementation:

@property (nonatomic, strong) UIActivityIndicatorView *spinner;
@property (nonatomic, strong) UIAlertController *alertController;


// in init:

_alertController = [UIAlertController alertControllerWithTitle: @"Loading"
                                                         message: nil
                                                  preferredStyle: UIAlertControllerStyleAlert];
_spinner = [UIActivityIndicatorView new];
_spinner.translatesAutoresizingMaskIntoConstraints = false;
_spinner.userInteractionEnabled = false;
_spinner.color = [ThemingAssistant tintColor];
_spinner.frame = _alertController.view.bounds;
_spinner.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
[_spinner startAnimating];
[_alertController.view addSubview: _spinner];


// ...

- (void) showOn: (UIViewController *)target
          title: (NSString *)title
        message: (NSString *)message
      canCancel: (BOOL)canCancel
{
    self.alertController.title = title;
    self.alertController.message = message;

    if (canCancel)
    {
        [self.alertController addAction:[UIAlertAction actionWithTitle: @"Cancel"
                                                                 style: UIAlertActionStyleCancel
                                                               handler: ^(UIAlertAction *name){
                                                                   [self customDismiss];
                                                               }]];
    }

    NSDictionary *views = @{@"pending"   : self.alertController.view,
                            @"indicator" : self.spinner};
    NSArray *constraints =
    [NSLayoutConstraint constraintsWithVisualFormat: @"V:[indicator]-(-50)-|"
                                            options: 0
                                            metrics: nil
                                              views: views];
    [constraints arrayByAddingObjectsFromArray:
     [NSLayoutConstraint constraintsWithVisualFormat: @"H:|[indicator]|"
                                             options: 0
                                             metrics: nil
                                               views: views]];


    [target presentViewController: self.alertController
                         animated: true
                       completion: nil];
}

Even if this was in the white rectangle, I fear it might run into text (also, when I get it in there, I want it to be in the middle-top, much like MBProgressHUD does), so I'll need a way to reserve some space for it.

So, my question is two-fold: How do I reserve space for a UIActivityIndicatorView in a UIAlertController's white rectangle, and then how do I actually place it in there?

Like JonasG mentioned here there is a property named contentViewController and we can use KVC for access

Example :

UIViewController *v = [[UIViewController alloc] init];
v.view.backgroundColor = [UIColor redColor];

[alertController setValue:v forKey:@"contentViewController"];

So here is how your code should looks like (tested and works fine) :

- (IBAction)buttonClicked:(id)sender
{

    self.alertController = [UIAlertController alertControllerWithTitle: @"Loading"
                                                           message: nil
                                                    preferredStyle: UIAlertControllerStyleAlert];


    [self.alertController addAction:[UIAlertAction actionWithTitle: @"Cancel" style: UIAlertActionStyleCancel handler:nil]];


    UIViewController *customVC     = [[UIViewController alloc] init];


    UIActivityIndicatorView* spinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
    [spinner startAnimating];
    [customVC.view addSubview:spinner];


    [customVC.view addConstraint:[NSLayoutConstraint
                           constraintWithItem: spinner
                           attribute:NSLayoutAttributeCenterX
                           relatedBy:NSLayoutRelationEqual
                           toItem:customVC.view
                           attribute:NSLayoutAttributeCenterX
                           multiplier:1.0f
                           constant:0.0f]];



    [customVC.view addConstraint:[NSLayoutConstraint
                           constraintWithItem: spinner
                           attribute:NSLayoutAttributeCenterY
                           relatedBy:NSLayoutRelationEqual
                           toItem:customVC.view
                           attribute:NSLayoutAttributeCenterY
                           multiplier:1.0f
                           constant:0.0f]];


    [self.alertController setValue:customVC forKey:@"contentViewController"];


    [self presentViewController: self.alertController
                         animated: true
                       completion: nil];

}

You can override -preferredContentSize to return a custom size in the view controller that you are setting as contentViewController.

in our case it's customVC

Result:

Want the text to be below the indicator ?

I have created a UIViewController with an xib to act as a custom controller for our contentViewController in the first example we have created the view controller without xib file, Now we can add views using interface builder, I have added an Activity indicator and set the constraints to be centered horizontally and vertically and a label under the activity indicator which is centered horizontally here is my interface builder:

we have less code now:

- (IBAction)buttonClicked:(id)sender
{

    self.alertController = [UIAlertController alertControllerWithTitle: nil
                                                           message: nil
                                                    preferredStyle: UIAlertControllerStyleAlert];

    MyCustomViewController *v     = [[MyCustomViewController alloc] init];

    [self.alertController setValue:v forKey:@"contentViewController"];
    [self presentViewController: self.alertController animated: true  completion: nil];

}

Result :