I build a ScreenSaver using swift 4.2 but it doesn't work

Hello everyone, I'm a newer to Swift and macOS Development.

I want to build a ScreenSaver to start my macOS development life, but I have encountered some problems:

First I read this blog post Creating a macOS screensaver and create an Xcode project.

Then I create a

MainView.swift

.h

.m

import ScreenSaver

class MainView: ScreenSaverView {

    override init?(frame: NSRect, isPreview: Bool) {
        super.init(frame: frame, isPreview: isPreview)
    }
   
    required init?(coder: NSCoder) {
        super.init(coder: coder)
    }
   
    override func draw(_ rect: NSRect) {
        super.draw(rect)

        // Drawing code here.
        NSColor.black.setFill()
        bounds.fill()
        NSColor.white.set()
       
        let hello: String = "Hello world!"
       
        hello.draw(at: NSPoint(x: 100.0, y: 100.0), withAttributes: nil)
    }
   
}

I know I need to change the

Principal class

MainView

Always Embed Swift Standard Libraries

Yes

Then I build my project and double-click

.saver

You cannot use the ... screen saver with this version of OS X. Please contact the vendor to get a newer version of the screen saver.

Xcode version is Version 10.1 (10B61)

Swift version is 4.2

macOS version is 10.14.1 (18B75)