How can I run swift code in Struct ContentView - swift

Question

I'm very new to SwiftUI and Xcode and very less knowledge in Class, Stuct and function() in Swift. I'm trying to put my code inside to ContentView View{}. Because I couldn't see the result of this code on the (UI)user interface. Also, I couldn't find a good article on how this code runs in Sturct ContnetView.Here is the code I want to run.
import Cocoa
let options = CGWindowListOption(arrayLiteral: .excludeDesktopElements, .optionOnScreenOnly)
let windowsListInfo = CGWindowListCopyWindowInfo(options, CGWindowID(0))
let infoList = windowsListInfo as! [[String:Any]]
let visibleWindows = infoList.filter{ $0["kCGWindowLayer"] as! Int == 0 }
print(visibleWindows)
ContentView looks like,
import SwiftUI
struct ContentView: View {
var body: some View {
Text("Hello, world!")
.padding()
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
When I put code inside to View{}. It gives errors.

Answer 1

Think of your SwiftUI code like "View Builder Code". The first snippet you provided is "Logical Code".
Your SwiftUI View Builder code is intended to describe your view. When you add logical code in there, SwiftUI wouldn't know when to run it.
For instance, you can tell SwiftUI to run the code when the view appears using the .onAppear modifier.
Text("Hello, world!")
.padding()
.onAppear {
// Your Logical Code
let options = CGWindowListOption(arrayLiteral: .excludeDesktopElements, .optionOnScreenOnly)
let windowsListInfo = CGWindowListCopyWindowInfo(options, CGWindowID(0))
let infoList = windowsListInfo as! [[String:Any]]
let visibleWindows = infoList.filter{ $0["kCGWindowLayer"] as! Int == 0 }
print(visibleWindows)
}
For your use case, you might want to consider creating a #State variable with an array of visibleWindows or even a computed property.