Swift callback function for draw()? - ios

Question

I have a customView where I overwrite drawRect:. I also have some cases, where I want to display a UILabel ontop of my customView:
if self.ticks.count < 50 {
self.label.frame = self.bounds
self.label.text = "This chart requires 50 or more ticks.\nKeep Ticking."
self.addSubview(label)
}
However if I call this code before the drawRect is called, then my label doesn't show up. Is there a callback method like viewDidDraw or something?
EDIT
Someone asked for it, so here is all the code that is now doing what I need it to do. I think the answer to the question is to override layoutSubviews.
#IBDesignable open class CustomView: UIView {
#objc open var ticks:[Tick] = []
let label = UILabel()
required public init?(coder: NSCoder) {
super.init(coder: coder)
setup()
}
required public override init(frame: CGRect) {
super.init(frame: frame)
setup()
}
func setup(){
self.backgroundColor = UIColor.clear
self.label.frame = self.bounds
self.label.text = "This chart requires 50 or more ticks.\nKeep Ticking."
self.label.numberOfLines = 0
self.label.textAlignment = .center
self.addSubview(label)
}
override open func layoutSubviews() {
self.label.frame = self.bounds
}
#objc open func setSessions(sessions:[Session]){
self.ticks = []
for session in sessions.reversed(){
if self.ticks.count < 250{
self.ticks = self.ticks + (session.getShots() as! [Shot])
}else{
break
}
}
if self.ticks.count < 50 {
self.label.isHidden = false
}else{
self.label.isHidden = true
}
self.bringSubview(toFront: self.label)
}
override open func draw(_ rect: CGRect) {
let context = UIGraphicsGetCurrentContext()!
let width = rect.width - 10;
let height = rect.height - 10;
let center = CGPoint(x: width/2+5, y: height/2+5)
let big_r = min(width, height)/2
context.setLineWidth(1.5)
UIColor.white.setStroke()
//draw the rings
for i in stride(from: 1, to: 7, by: 1){
let r = big_r * CGFloat(i) / 6.0;
context.addArc(center:center, radius:r, startAngle: 0, endAngle: CGFloat(2*Double.pi), clockwise: false)
context.strokePath()
}
//draw the ticks
if self.ticks.count > 49 {
UIColor.red().setFill()
for (i, tick) in self.ticks.prefix(250).enumerated(){
let radius = min((100.0-CGFloat(shot.score))/30.0 * big_r, big_r);
let x = Utilities.calculateX(tick, radius)
let y = Utilities.calculateY(tick, radius)
let point = CGPoint(x: x+center.x,y: y+center.y)
context.addArc(center:point, radius:CGFloat(DOT_WIDTH/2), startAngle: 0, endAngle: CGFloat(2*Double.pi), clockwise: false)
context.fillPath()
}
}
}
}

Answer 1

You can make your custom view redraw by calling setNeedsDisplay() when needed. After that, you can add the label

Answer 2

You can set a delegation for the View class and call the delegate method at the end of the draw function. However, it seems that if you call that directly, the draw function will only end until the delegate function get processed. Which means that the code will be executed before the new drawing refresh on the screen. In that case, you may need to call it asynchronously.
// at end of draw function
DispatchQueue.main.async {
self.delegate?.drawEnd()
}