NSView draw() being called twice - swift

Question

I'm new to swift and Cocoa dev my problem is:-
NSView's draw() function is being called twice. the results and code are below :-
results
[3/3] Linking MyCanvasApp
Hello, World
You got nothing.
You got nothing.
^C
as you can see "You got nothing" is being printed twice
PS everything is handwritten I'm not using Xcode at all
main.swift
import Cocoa
var app = NSApplication.shared
app.setActivationPolicy(.regular)
let delegate = AppDelegate()
app.delegate = delegate
app.activate(ignoringOtherApps: true)
app.run()
AppDelegate.swift
import Cocoa
class AppDelegate: NSObject, NSApplicationDelegate {
func applicationDidFinishLaunching(_ aNotification: Notification) {
print("Hello, World")
let frame = NSRect.init(x: 100.0, y: 100.0, width: 300.0, height: 300.0)
let win = NSWindow.init(contentRect: frame, styleMask: [.closable, .titled], backing: .buffered, defer: false)
win.title = "My Canvas App"
win.makeKeyAndOrderFront(nil)
let frame2 = NSRectToCGRect(NSRect.init(x: 0, y: 0, width: 300.0, height: 300.0))
let canvas = CanvasView.init(frame: frame2)
win.contentView!.addSubview(canvas)
}
}
does NSView.init (CanvasView.init) calls it or something? ^^
CanvasView.swift
import Cocoa
class CanvasView: NSView {
var Mode: CanvasMode = CanvasMode.Rectangle
override init(frame: CGRect) {
super.init(frame: frame)
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
override func draw(_ rect: CGRect) {
// super.draw(rect)
// var context: CGContext = NSGraphicsContext.current!.CGContext
self.wantsLayer = true
self.layer?.backgroundColor = NSColor.yellow.cgColor
switch Mode {
case .Line:
print("You got Line.")
default:
print("You got nothing.")
}
}
override func mouseDown(with theEvent: NSEvent) {
print("left mouse")
}
override func rightMouseDown(with theEvent: NSEvent) {
print("right mouse")
}
override func mouseDragged(with theEvent: NSEvent) {
print("mouseDragged")
}
}
CanvasMode.swift
import Cocoa
enum CanvasMode {
case Line
case Rectangle
case Triangle
}