example.m

//
//  ViewController.m
//  PopupTest
//
//  Created by Chris Hamons on 10/7/19.
//  Copyright © 2019 Chris Hamons. All rights reserved.
//

@import MetalKit;

#import "ViewController.h"

@implementation ViewController

NSTextView * textView;
NSDate *lastTick;

- (void)viewDidLoad {
    [super viewDidLoad];
    MTKView * timer = [[MTKView alloc] initWithFrame:CGRectMake(0, 0, 10, 10) device:MTLCreateSystemDefaultDevice()];
    timer.clearColor = MTLClearColorMake(1, 0, 0, 1);
    timer.delegate = self;
    [self.view addSubview:timer];
    
    textView = [[NSTextView alloc] initWithFrame:CGRectMake(0, 0, 200, 50)];
    [self.view addSubview:textView];
    
    lastTick = [NSDate date];
    
    
    NSMenuItem *first = [[NSMenuItem alloc] initWithTitle:@"1" action:NULL keyEquivalent:@""];
    NSMenuItem *second = [[NSMenuItem alloc] initWithTitle:@"2" action:NULL keyEquivalent:@""];
    NSMenuItem *third = [[NSMenuItem alloc] initWithTitle:@"3" action:NULL keyEquivalent:@""];
    
    NSPopUpButton *button = [[NSPopUpButton alloc] initWithFrame:NSMakeRect(50, 50, 50, 50)pullsDown:YES];
    [button.menu addItem:first];
    [button.menu addItem:second];
    [button.menu addItem:third];
    [self.view addSubview:button];
}

- (void)mtkView:(nonnull MTKView *)view drawableSizeWillChange:(CGSize)size{
}

- (void)drawInMTKView:(nonnull MTKView *)view {
    NSDate *currentDate = [NSDate date];
    NSTimeInterval timeInterval = [currentDate timeIntervalSinceDate:lastTick];

    NSString *intervalString = [NSString stringWithFormat:@"%f", timeInterval];
    textView.string = intervalString;
    
    lastTick = [NSDate date];
}

@end