Drawing lines with core graphics - ios

Question

I want to draw more than one straight line in core graphics. or save the line and start a new one. I used two variables for touch location and assigned touch location to them in touch Began,Moved,Ended then I used this:
override func draw(_ rect: CGRect) {
let context = UIGraphicsGetCurrentContext()
context?.setStrokeColor(UIColor(red: 0, green: 0, blue: 0, alpha: 1.0).cgColor)
context?.setLineWidth(5.0)
context?.move(to: CGPoint(x: firstTouchLocation.x, y: firstTouchLocation.y))
context?.addLine(to: CGPoint(x: lastTouchLocation.x, y: lastTouchLocation.y))
context?.strokePath()
}
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
if let touch = touches.first {
firstTouchLocation = touch.location(in: self)
lastTouchLocation = firstTouchLocation
setNeedsDisplay()
}
}
override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
if let touch = touches.first {
lastTouchLocation = touch.location(in: self)
setNeedsDisplay()
}
}
override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
if let touch = touches.first {
lastTouchLocation = touch.location(in: self)
setNeedsDisplay()
}
}

Answer 1

Try drawing the line using CAShapeLayer like so:
func addLine(fromPoint start: CGPoint, toPoint end:CGPoint) {
let line = CAShapeLayer()
let linePath = UIBezierPath()
linePath.move(to: start)
linePath.addLine(to: end)
line.path = linePath.cgPath
line.strokeColor = UIColor.red.cgColor
line.lineWidth = 1
line.lineJoin = kCALineJoinRound
self.view.layer.addSublayer(line)
}
Hope this helps!

Answer 2

You got to have a model object which represent a line say ex: LineAnnotation. LineAnnotation will hold start and end points, color and many others details about the line. Hold every LineAnnotation(line) in an array. Iterate through this array and draw line one by one. In your case are drawing using latest data. Previous points which are drawn will e refreshed when you call setNeedsDisplay()

Answer 3

As per apples documentation(https://developer.apple.com/documentation/uikit/uiview/1622437-setneedsdisplay) setNeedsDisplay method redraws your view, so you are left with fresh view with latest line only.
To solve your problem simply pull your code in a method and call that method whenever you made a touch.
override func draw(_ rect: CGRect) {
drawLine()
}
func drawLine()
{
let context = UIGraphicsGetCurrentContext()
context?.setStrokeColor(UIColor(red: 0, green: 0, blue: 0, alpha: 1.0).cgColor)
context?.setLineWidth(5.0)
context?.move(to: CGPoint(x: firstTouchLocation.x, y: firstTouchLocation.y))
context?.addLine(to: CGPoint(x: lastTouchLocation.x, y: lastTouchLocation.y))
context?.strokePath()
}
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
if let touch = touches.first {
firstTouchLocation = touch.location(in: self)
lastTouchLocation = firstTouchLocation
drawLine()
}
}
override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
if let touch = touches.first {
lastTouchLocation = touch.location(in: self)
drawLine()
}
}
override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
if let touch = touches.first {
lastTouchLocation = touch.location(in: self)
drawLine()
}
}