Spinner (UIActivityIndicatorView) at the Center of View with AutoLayout

UIActivityIndicatorView  *spinner;

spinner =[[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];

[spinner setTranslatesAutoresizingMaskIntoConstraints:NO];

spinner.color=[UIColor blackColor];

    [self.view addSubview:spinner];

 NSLayoutConstraint *cont = [NSLayoutConstraint constraintWithItem:spinner attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0.0];

    [self.view addConstraint:cont];

 cont = [NSLayoutConstraint constraintWithItem:spinner attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1.0 constant:0.0];

    [self.view addConstraint:cont];

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 [spinner startAnimating];

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 [spinner stopAnimating];