How to show an AlertController in Objective C...

The below method is to show an Alert in a ViewController Wherever you want an alert you can call this method (if you implement it globally then no need to implement in every ViewController).

call this method like,    [self showAlert];

-(void) showAlert {

    UIAlertController *warningAlertController = [UIAlertController alertControllerWithTitle:@"Title Of your Alert" message:@"Here enter your alert message !" preferredStyle:UIAlertControllerStyleAlert];

    UIAlertAction *alertAction = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {

        // After click on Ok what you want to perform you can write here

    }];

    [warningAlertController addAction:alertAction];

    [self presentViewController:warningAlertController animated:YES completion:nil];

}

And if you want add few more actions you can add to it as shown below,

  UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {

        // After click on Cancel what you want to perform you can write here

    }];

    [warningAlertController addAction:cancelAction];