Drawing in cocoa swift - swift

Question

I've been trying to draw a simple line in a cocoa application using swift, however I fail to fully understand how to use the CGContext class.
I've created this class:
import Cocoa
class Drawing: NSView {
override func drawRect(dirtyRect: NSRect) {
super.drawRect(dirtyRect)
let context = NSGraphicsContext.currentContext()?.CGContext;
CGContextBeginPath(context)
CGContextMoveToPoint(context, 0, 0)
CGContextAddLineToPoint(context, 100, 100)
CGContextSetRGBStrokeColor(context, 1, 1, 1, 1)
CGContextSetLineWidth(context, 5.0)
CGContextStrokePath(context)
}
}
and used it in the main window like so
override func viewDidLoad() {
super.viewDidLoad()
let dr = Drawing()
self.view.addSubview(dr)
dr.drawRect(NSRect(x: 0, y: 0, width: 100, height: 100))
}
but it didn't do a thing

Answer 1

You need to initialise your Drawing view with a frame otherwise the system won't know where to draw it, like so:
override func viewDidLoad() {
super.viewDidLoad()
let dr = Drawing(frame: NSRect(x: 0, y: 0, width: 100, height: 100))
self.view.addSubview(dr)
}
Also as David said, you do not need to call drawRect yourself as it is automatically called by the system.

Answer 2

my 2 cents for swift 5.x Xcode 10:
override func draw(_ dirtyRect: NSRect) {
super.draw(dirtyRect)
guard let context = NSGraphicsContext.current?.cgContext else{
return
}
context.beginPath()
context.move(to: CGPoint.zero)
context.addLine(to: CGPoint( x: 100, y: 100))
context.setStrokeColor(CGColor( red: 1, green: 0, blue: 0, alpha: 1))
context.setLineWidth(5.0)
context.strokePath()
}

Answer 3

You don't need to add a view or use CoreGraphics instructions.
Simply do like this: ( EDIT: I added update exemple code )
class View: NSView {
var p1: NSPoint = .zero {
didSet { needsDisplay = true }
}
var p2: NSPoint = NSPoint(x: 100, y: 100) {
didSet { needsDisplay = true }
}
// Returns the rect using the two points
var rect: NSRect {
NSRect(x: p1.x, y: p1.y,
width: p2.x - p1.x, height: p2.y - p1.y)
}
// Draw a rectangle and its diagonal
override func draw(_ dirtyRect: NSRect) {
// Draw rect
let rect = self.rect
NSColor.red.setFill()
NSColor.black.setStroke()
rect.fill()
rect.stroke()
// Draw line
let path = NSBezierPath()
path.move(to: p1)
path.line(to: p2)
path.stroke()
}
}
Don't forget to call myView.needsDisplay = true to update content
From there, check auto completion to discover Cocoa drawing functions to draw paths, ovals, rounded rects. Cheers :)