Dynamically assigned UIFont does not show immediately in slow simulator - swift

Question

I have a UIView with a UILabel for which, I'd like allow the user to dynamically change the font size. The code below almost works, but the problem is that after the new UIFont is assigned to the label, it doesn't immediately show in the UI. Instead, some other UI activity is required to make it show up.
What I'm looking for is a technique where the font change will show up immediately after the gesture is over.
Starting with the technique shown in this tutorial, I added a gesture recognizer to the UIScrollView. In the associated UIViewController, I implemented handlePinch(UIpinchGestureRecognizer).
Inside that function, I take action only when the gesture begins and ends (no attempt to animate). If the user indicated zoom, I increase the font by 4 points. If the user indicated a shrink, I decrease the font by 4 points. This all works, except for the fact that the screen does not reflect the change until another UI function is executed. I have only tested this on the simulator, but I presume it would be the same on a real device.
I have tried setNeedsDisplay and setNeedsLayout and several other odd things on both the UILabel as well as the view that was passed to the handlePinch() function.
#IBAction func handlePinch(_ gesture: UIPinchGestureRecognizer) {
guard let gestureView = gesture.view else {
return;
}
gestureView.transform = gestureView.transform.scaledBy(x: gesture.scale, y: gesture.scale)
if (gesture.state == UIPinchGestureRecognizer.State.began) {
pinchD = gestureView.transform.d
print("pinch started ", pinchD)
}
if (gesture.state == UIPinchGestureRecognizer.State.ended) {
print("pinch ended ", gestureView.transform.d)
print("compare:", pinchD, gestureView.transform.d)
let larger = gestureView.transform.d > pinchD
let fontSize = multiLineLabel.font.pointSize
if (larger) {
if (fontSize < 28) {
let calculatedFont = UIFont(name: multiLineLabel.font.fontName, size: fontSize + 4)
print("bigger fontSize", fontSize + 4);
multiLineLabel.font = calculatedFont
}
} else {
if (fontSize > 12) {
let calculatedFont = UIFont(name: multiLineLabel.font.fontName, size: fontSize - 4)
print("smaller fontSize", fontSize - 4);
multiLineLabel.font = calculatedFont
}
}
}
}
What needs to be done after the calculatedFont is applied to the UILabel to make it show immediately in the app?
ADDITIONAL CLARIFICATION:
handlePinch() runs as expected; every time a pinch gesture ends, I see bigger fontSize... or smaller fontSize... logged.
After the logging, the simulator screen font size remains the same until I do one of several things. One thing that causes the font size to change is if I swipe to the next item. Before the animation starts, the font increases. The font changes also if I hit the back button (the font change shows briefly before the other view appears).

Answer 1

It turns out that my presumption was incorrect:
I have only tested this on the simulator, but I presume it would be the same on a real device.
I believe that was NOT correct.
I'm testing on a very, very old iMac and the simulator is bogged down such that it takes 15 or 30 seconds to update the screen!
So I conclude that the code is working fine after all.