I’m guessing your mySpinner
ivar isn’t being properly retained or declared.
In your .h file, declare it as a property. That is:
@property (strong) UIActivityIndicatorView *mySpinner;
then, when you create it:
self.mySpinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
and when you reference it in your button click method:
[self.mySpinner startAnimating];
solved IOS: Add activity indicatior view in web view