"Make a Custom UIGestureRecognizer in Objective-C" ViewController.m File and Selector Method.

ViewController.m

#import “ViewController.h”
#import “zLetterGestureRecognizer.h”

@interface ViewController ()
@end

@implementation ViewController
  - (void)viewDidLoad {
      [super viewDidLoad];
      [self.view addGestureRecognizer:[[ZLetterGestureRecognizer alloc] initWithTarget:self action:@selector(zLetterMade:)]];
  }

  -(void)zLetterMade:(ZLetterGestureRecognizer *)zLetterRecognizer {
      NSLog(@”Z letter made by the user!!”); //This will be printed when the gesture is recognized.
  }
@end