Drag a CGRect using UIPanGestureRecognizer - swift

Question

I am subclassing UIView, and am trying to "drag" a CGRect back and forth across the screen. Basically I want to move(redraw) the rectangle every time I drag my finger. So far, I have this code:
var rectangle: CGRect {
get {
return CGRect(x: 200,
y: 200,
width: frame.width / 6,
height: 15)
}
set {}
}
override func draw(_ rect: CGRect) {
let gesture = UIPanGestureRecognizer(target: self, action: #selector(dragRectangle(recognizer:)))
addGestureRecognizer(gesture)
drawRectangle(rect)
}
func drawRectangle(_ rect: CGRect) {
let path = UIBezierPath(rect: rectangle)
UIColor.black.set()
path.fill()
}
#objc func dragRectangle(recognizer: UIPanGestureRecognizer) {
let translation = recognizer.translation(in: self)
rectangle = CGRect(x: rectangle.midX + translation.x, y: rectangle.midY + translation.y, width: rectangle.width, height: rectangle.height)
setNeedsDisplay()
recognizer.setTranslation(CGPoint.zero, in: self)
}
This is my first time using UIPanGestureRecognizer, so I'm not sure of all the details that go into this. I have set breakpoints in drawRectangle and confirmed that this is being called. However, the rectangle on the screen does not move at all, no matter how many times I try to drag it. What's wrong?

Answer 1

This is how you can do it easily. just copy paste and run this.
//
// RootController.swift
// SampleApp
//
// Created by Chanaka Caldera on 24/6/19.
// Copyright © 2019 homeapps. All rights reserved.
//
import UIKit
class RootController: UIViewController {
private var draggableView: UIView!
private var pangesture: UIPanGestureRecognizer!
override func viewDidLoad() {
super.viewDidLoad()
setdragview()
}
}
extension RootController {
fileprivate func setdragview() {
draggableView = UIView()
draggableView.translatesAutoresizingMaskIntoConstraints = false
draggableView.backgroundColor = .lightGray
view.addSubview(draggableView)
let draggableviewConstraints = [draggableView.leftAnchor.constraint(equalTo: view.leftAnchor,constant: 10),
draggableView.topAnchor.constraint(equalTo: view.topAnchor, constant: 64),
draggableView.widthAnchor.constraint(equalToConstant: 100),
draggableView.heightAnchor.constraint(equalToConstant: 40)]
NSLayoutConstraint.activate(draggableviewConstraints)
pangesture = UIPanGestureRecognizer()
draggableView.isUserInteractionEnabled = true
draggableView.addGestureRecognizer(pangesture)
pangesture.addTarget(self, action: #selector(draggableFunction(_:)))
}
}
extension RootController {
#objc fileprivate func draggableFunction(_ sender: UIPanGestureRecognizer) {
view.bringSubviewToFront(draggableView)
let translation = sender.translation(in: self.view)
draggableView.center = CGPoint(x: draggableView.center.x + translation.x, y: draggableView.center.y + translation.y)
sender.setTranslation(CGPoint.zero, in: self.view)
print("drag works : \(translation.x)")
}
}
here is the demo,
Hope this will help. cheers !

Answer 2

Try like this (check comments through code):
#IBDesignable
class Rectangle: UIView {
#IBInspectable var color: UIColor = .clear {
didSet { backgroundColor = color }
}
// draw your view using the background color
override func draw(_ rect: CGRect) {
backgroundColor?.set()
UIBezierPath(rect: rect).fill()
}
// add the gesture recognizer to your view
override func didMoveToSuperview() {
addGestureRecognizer(UIPanGestureRecognizer(target: self, action: #selector(pan)))
}
// your gesture selector
#objc func pan(_ gesture: UIPanGestureRecognizer) {
// update your view frame origin
frame.origin += gesture.translation(in: self)
// reset the gesture translation
gesture.setTranslation(.zero, in: self)
}
}
extension CGPoint {
static func +=(lhs: inout CGPoint, rhs: CGPoint) {
lhs.x += rhs.x
lhs.y += rhs.y
}
}
To draw rectangles on your view when panning you can do as follow:
import UIKit
class ViewController: UIViewController {
var rectangles: [Rectangle] = []
override func viewDidLoad() {
super.viewDidLoad()
view.addGestureRecognizer(UIPanGestureRecognizer(target: self, action: #selector(pan)))
}
#objc func pan(_ gesture: UIPanGestureRecognizer) {
switch gesture.state {
case .began:
let rectangle = Rectangle(frame: .init(origin: gesture.location(in: view), size: .init(width: 0, height: 0)))
rectangle.fillColor = .red
rectangle.strokeColor = .white
rectangle.lineWidth = 3
view.addSubview(rectangle)
rectangles.append(rectangle)
case .changed:
let distance = gesture.translation(in: view)
let index = rectangles.index(before: rectangles.endIndex)
let frame = rectangles[index].frame
rectangles[index].frame = .init(origin: frame.origin, size: .init(width: frame.width + distance.x, height: frame.height + distance.y))
rectangles[index].setNeedsDisplay()
gesture.setTranslation(.zero, in: view)
case .ended:
break
default:
break
}
}
}
Sample Project

Answer 3

I figured out most of the problem as to why the rectangle wasn't moving. It turns out that I misunderstood how variable getters and setters work in Swift. Nevertheless, I changed this code:
var rectangle: CGRect {
get {
return CGRect(x: 200,
y: 200,
width: frame.width / 6,
height: 15)
}
set {}
}
to be a lazy variable:
lazy var rectangle: CGRect = {
return CGRect(x: 200,
y: 200,
width: self.frame.width / 6,
height: 15)
}()
The reason I needed get and set in the first place was because I use frame in my variable calculations, and that was not available until the view itself was fully instantiated. I also tweaked this code a bit:
rectangle = CGRect(x: rectangle.midX + translation.x, y: rectangle.midY + translation.y, width: rectangle.width, height: rectangle.height)
and used minX instead of midX:
rectangle = CGRect(x: rectangle.minX + translation.x, y: rectangle.minY + translation.y, width: rectangle.width, height: rectangle.height)
This is because CGRect is initialized with the x and y parameters being the minX and minY.
This is good progress(at least the rectangle moves). However, I am not able to figure out why the rectangle only switches places after I have released my mouse, resulting in choppy movement.