Using Auto Layout Constraints for Drag, Pinch, Zoom and Tap

DragZoomPinch.swift

import UIKit
import PlaygroundSupport

class ViewController: UIViewController {
    var redView:UIView!
    var movedRight:Bool = false
    var verticalConstraint:NSLayoutConstraint!
    var horizontalConstraint:NSLayoutConstraint!
    var widthConstraint:NSLayoutConstraint!
    var heightConstraint:NSLayoutConstraint!
    
    var offSet:CGPoint!
    var transform: CGAffineTransform!
    var viewSize:CGSize!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        redView = UIView(frame: CGRect(x: 100, y: 100, width: 200, height: 200))
        redView.backgroundColor = .red
        
        view.addSubview(redView)
        let taps = UITapGestureRecognizer(target: self, action: #selector(tap))
        redView.addGestureRecognizer(taps)
        let drags = UIPanGestureRecognizer(target: self, action: #selector(drag))
        redView.addGestureRecognizer(drags)
        let pinches = UIPinchGestureRecognizer(target: self, action: #selector(pinch))
        redView.addGestureRecognizer(pinches)
        let rotates = UIRotationGestureRecognizer(target: self, action: #selector(rotate))
        redView.addGestureRecognizer(rotates)
        redView.isUserInteractionEnabled = true
        alignView(viewToConstrain: redView)
        
        
    }
    
    @objc func rotate(gest:UIRotationGestureRecognizer) {
        //        view.layoutIfNeeded()
        
        let rotation = gest.rotation
        if let viewToTransform = gest.view {
            switch (gest.state) {
            case .began:
                transform = viewToTransform.transform
                break;
                
            case .changed:
                viewToTransform.transform = transform.concatenating(CGAffineTransform(rotationAngle: rotation))
                break;
                
                
            case .ended:
                break;
                
            default:
                break;
            }
            
        }
        
    }
    
    // see http://stackoverflow.com/a/21803627/1694526
    @objc func drag(gest:UIPanGestureRecognizer) {
        view.layoutIfNeeded()
        
        let translation = gest.translation(in: self.view)
        switch (gest.state) {
        case .began:
            offSet = CGPoint(x: horizontalConstraint.constant, y: verticalConstraint.constant)
            break;
            
        case .changed:
            horizontalConstraint.constant = offSet.x + translation.x
            verticalConstraint.constant = offSet.y + translation.y
            
            view.layoutIfNeeded()
            break;
            
            
        case .ended:
            break;
            
        default:
            break;
        }
        
    }
    @objc func pinch(gest:UIPinchGestureRecognizer) {
        view.layoutIfNeeded()
        let scale = gest.scale
        switch (gest.state) {
        case .began:
            viewSize = CGSize(width: widthConstraint.constant, height: heightConstraint.constant)
            break;
            
        case .changed:
            widthConstraint.constant = viewSize.width * scale
            heightConstraint.constant = viewSize.height * scale
            view.layoutIfNeeded()
            break;
            
        case .ended:
            break;
            
        default:
            break;
        }
        
    }
    
    @objc func tap(gest:UITapGestureRecognizer) {
        if movedRight {
            self.view.layoutIfNeeded()
            self.verticalConstraint.constant += 25
            UIView.animate(withDuration: 0.5){
                self.view.layoutIfNeeded()
                
            }
            
            movedRight = false
            
        }
        else {
            self.view.layoutIfNeeded()
            UIView.animate(withDuration: 0.5){
                self.horizontalConstraint.constant += 25
                self.view.layoutIfNeeded()
                
            }
            movedRight = true
            
        }
    }
    
    func alignView(viewToConstrain:UIView) {
        // a precaution
        viewToConstrain.removeConstraints(viewToConstrain.constraints)
        // enable AutoLayout
        viewToConstrain.translatesAutoresizingMaskIntoConstraints = false
        // set horizontal and vertical constraints
        horizontalConstraint =  viewToConstrain.centerXAnchor.constraint(equalTo: view.centerXAnchor)
        horizontalConstraint.isActive = true
        verticalConstraint = viewToConstrain.centerYAnchor.constraint(equalTo: view.centerYAnchor)
        verticalConstraint.isActive = true
        // set height and width anchors
        heightConstraint =  viewToConstrain.heightAnchor.constraint(equalToConstant: viewToConstrain.frame.height)
        heightConstraint.isActive = true
        widthConstraint = viewToConstrain.widthAnchor.constraint(equalToConstant: viewToConstrain.frame.width)
        widthConstraint.isActive = true
    }
}
let aVC = ViewController()

PlaygroundPage.current.liveView = aVC

My UILabel jumps to initial position when I change its font programmatically. I have a button for that. What could be wrong?

I wrote this code a long time ago, so I'm working from memory here, but the jumping issue occurs because the constraint values are not updated, or a refresh of the values is triggered. This is the reason for all the .changed cases. I'd look at what's happening in the redrawing of the label when the font changes. It might be being thrown back to its original position because the whole thing is being redrawn.

Thank you so much @sketchytech. I managed to achieve that by updating constraint constant value and it is now working fine.

Brilliant, @shoaibahmaddx thanks for taking the time to add the update, really pleased it worked.