Minimal Swift App

MiniApp.swift

#!/usr/bin/swift
import AppKit

let application = NSApplication.shared

let fileOpenPanel = NSOpenPanel(), fileSavePanel = NSSavePanel()

let window: NSWindow = { window in
   window.setContentSize(NSSize(width:800, height:600))
   window.styleMask = [.titled, .closable, .miniaturizable]
   window.center()
   window.title = "Minimal Swift App"
   return window
}(NSWindow())

window.makeKeyAndOrderFront(window)

extension NSButton {
   
   static func makeButton(title: String, target: AnyObject?, action: Selector) -> NSButton {
      let button = NSButton()
      button.title = title
      button.target = target
      button.action = action
      button.bezelStyle = .rounded
      return button
   }
}

class Delegate: NSObject, NSApplicationDelegate, NSWindowDelegate, NSTextFieldDelegate {
   
   var window: NSWindow
   var textField = NSTextField()
   var stack = NSStackView()
   var imageView = NSImageView()
   var mainStackView = NSStackView(frame: NSRect(x: 15, y: 15, width: 770, height: 570))

   init(window: NSWindow) { 
      textField.isEditable = true
      self.window = window
      super.init() 
      textField.delegate = self

      window.contentView!.addSubview(mainStackView)

      imageView.imageFrameStyle = .grayBezel

      let fileOpenButton = NSButton.makeButton(title: "File Open", target: delegate, action: #selector(Delegate.fileOpen(_:))),
      fileSaveButton = NSButton.makeButton(title: "File Save", target: delegate, action: #selector(Delegate.fileSave(_:)))

      if #available(iOS 9, OSX 10.11, *) {
         mainStackView.addArrangedSubview(stack);mainStackView.addArrangedSubview(imageView);mainStackView.orientation = .vertical 
         stack.addArrangedSubview(fileOpenButton);stack.addArrangedSubview(fileSaveButton);stack.addArrangedSubview(textField)
      }  
   }

   func applicationDidFinishLaunching(_ notification: Notification) { }
   
   func windowWillClose(_ notification: Notification) {
      NSApplication.shared.stop(0)
   }
   
   override func controlTextDidEndEditing(_ obj: Notification) {
      if let textField = obj.object as? NSTextField, let url = URL(string: textField.stringValue) {
         imageView.image = NSImage(contentsOf: url)
      }
   }
   
   @objc func fileOpen(_ sender: AnyObject) {
      fileOpenPanel.runModal()
      if let url = fileOpenPanel.urls.first {
         textField.stringValue = url.absoluteString
         imageView.image = NSImage(contentsOf: url)
      }
   }
   
   @objc func fileSave(_ sender: AnyObject) {
      fileSavePanel.allowedFileTypes = ["png"]
      fileSavePanel.runModal()
      guard let url = fileSavePanel.url, let rep = imageView.image?.representations.first as? NSBitmapImageRep else { return }
      let _ = try? rep.representation(using: .png, properties: [:])?.write(to: url, options: [])
   }
}

let delegate = Delegate(window: window)

application.delegate = delegate
window.delegate = delegate

application.activate(ignoringOtherApps: true)
application.setActivationPolicy(.regular)
application.run()