How to remove only one line from LineView? - ios

Question

by my code I can draw multiple straight lines one by one on a view.
now what I want is, to remove only one line when click Undo button.
I have write single line to remove last draw line in undoButtonAction, but it removes whole view.
i have search a lot and trying different solutions
what can I do? please suggest some hint.
#view Controller
import UIKit
class Line {
var startPoint : CGPoint?
var endPoint : CGPoint?
init(startPoint : CGPoint?, endPoint : CGPoint?) {
self.startPoint = startPoint
self.endPoint = endPoint
}
}
class ViewController: UIViewController {
var counter = 0
var lastPosition : CGPoint?
var firstPosition : CGPoint?
let shapeLayer = CAShapeLayer()
let path = UIBezierPath()
let canvas = CanvasView()
var lines = [Line]()
func setup(){
self.view.backgroundColor = UIColor.cyan
shapeLayer.path = path.cgPath
shapeLayer.strokeColor = UIColor.blue.cgColor
shapeLayer.lineWidth = 2.0
self.view.layer.addSublayer(shapeLayer)
let undoButton = UIButton(frame: CGRect(x: self.view.center.x - 50, y: self.view.frame.maxY - 100, width: 100, height: 30))
undoButton.setTitle("Undo", for: .normal)
undoButton.backgroundColor = .systemYellow
undoButton.addTarget(self, action: #selector(undoButtonAction), for: .touchUpInside)
self.view.addSubview(undoButton)
}
#objc func undoButtonAction(){
lines.popLast()
self.view.layer.removeFromSuperlayer()
}
override func viewDidLoad() {
super.viewDidLoad()
self.setup()
}
func drawLineFromPoint(start : CGPoint, toPoint end:CGPoint, ofColor lineColor: UIColor, inView view:UIView) {
let path = UIBezierPath()
path.move(to: start)
path.addLine(to: end)
let shapeLayer = CAShapeLayer()
shapeLayer.path = path.cgPath
shapeLayer.strokeColor = lineColor.cgColor
shapeLayer.lineWidth = 2.0
view.layer.addSublayer(shapeLayer)
}
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
if let touch = touches.first{
let position = touch.location(in: view)
self.firstPosition = position
self.lastPosition = position
path.move(to: firstPosition!)
path.addLine(to: lastPosition!)
print(position)
}
}
override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
if let touch = touches.first{
let lastlocation = touch.location(in: view)
path.removeAllPoints()
lastPosition = lastlocation
path.move(to: firstPosition!)
path.addLine(to: lastPosition!)
shapeLayer.path = path.cgPath
}
}
override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
let line = Line(startPoint: firstPosition, endPoint: lastPosition)
lines.append(line)
drawLineFromPoint(start: line.startPoint!, toPoint: line.endPoint!, ofColor: .systemBlue, inView: view)
}
}
#LineView
import Foundation
import UIKit
class LineView: UIView {
var points = [CGPoint]()
var lines = [[CGPoint]]()
var fpoint : CGPoint?
func clearLine(){
lines.append([CGPoint]())
}
}

Answer 1

Search your lines array for the line you want to remove i.e lines[2] and call removeFromSuperView()
lines[2].removeFromSuperView()

Answer 2

First add new variable in Line
class Line {
var startPoint : CGPoint?
var endPoint : CGPoint?
var name : String?
init(startPoint : CGPoint?, endPoint : CGPoint?, name : String?) {
self.startPoint = startPoint
self.endPoint = endPoint
self.name = name
}
}
Now when you are adding a line, provide random name using below function as randomString(length: 16)
func randomString(length: Int) -> String {
let letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
return String((0..<length).map{ _ in letters.randomElement()! })
}
Also update below methods
override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
var randomString : String = randomString(length: 16)
let line = Line(startPoint: firstPosition, endPoint: lastPosition, randomString)
lines.append(line)
drawLineFromPoint(start: line.startPoint!, toPoint: line.endPoint!, ofColor: .systemBlue, inView: view, name : randomString)
}
func drawLineFromPoint(start : CGPoint, toPoint end:CGPoint, ofColor lineColor: UIColor, inView view:UIView, name : String) {
let path = UIBezierPath()
path.move(to: start)
path.addLine(to: end)
let shapeLayer = CAShapeLayer()
shapeLayer.path = path.cgPath
shapeLayer.strokeColor = lineColor.cgColor
shapeLayer.name = name
shapeLayer.lineWidth = 2.0
view.layer.addSublayer(shapeLayer)
}
So each layer, you have name identifier.
Now while doing undo, do below
#objc func undoButtonAction(){
var lastLineObject : Line = lines[lines.count-1]
guard let sublayers = self.view.layer.sublayers else { return }
if let tempLayer = sublayers.first(where: {$0.name == lastLineObject.name ?? ""}) {
print("Found it: \(layer)")
tempLayer.removeFromSuperlayer()
lines.remove(at : lines.count - 1)
}
}
Note this is just idea and not real code.