SwiftUI how to run a func after another is fully completed - swift

Question

I am running a func that goes into a for loop and append to a an array. In the next line I am running another func that uses the first element of that array, however, the app crashes since at the time of the 2nd func execution it finds the array empty. I trued using sync() queue and completion handlers but still have the issue. The only way that it is working at the moment is to call a Timer to wait for a few seconds but that is not ideal way to do it of course. Do you have any suggestions?
The 1st func is as follows:
func openRun () {
let openPanel = NSOpenPanel()
...
if result.rawValue == NSApplication.ModalResponse.OK.rawValue {
let rawURL = openPanel.url!.path
//some codes that extract image files from the openned path
for image in imageList {
images.append(newImage)
}
}
}

Answer 1

It is hard to see, what you try to do. Check next Playground snippet which use NSOpenPanel to select some .swift file(s) and asynchronously (random delay mimics the real world usage) calculates length of its absolute path and show the results in SwiftUI View.
//: A Cocoa based Playground to present user interface
import AppKit
import SwiftUI
import PlaygroundSupport
let panel = NSOpenPanel()
panel.allowsMultipleSelection = true
panel.allowedFileTypes = ["swift"]
struct Info: Identifiable {
let id = UUID()
let txt: String
let length: Int
}
struct ContentView: View {
#State var arr: [Info] = []
var body: some View {
VStack {
Button(action: {
panel.begin { (respond) in
panel.urls.forEach { (url) in
self.urlLength(url: url) { (i) in
self.arr.append(Info(txt: url.lastPathComponent, length: i))
}
}
}
}) {
Text("action")
}.padding()
List(arr) { (item) in
HStack {
Text(item.txt)
Text(item.length.description).foregroundColor(Color.yellow)
}
}
}.frame(width: 200, height: 400)
.border(Color.red)
}
func urlLength(url: URL, completion: #escaping (Int)->()) {
DispatchQueue.global().asyncAfter(deadline: .now() + Double.random(in: 0.0 ..< 3.0)) { [url] in
let c = url.absoluteString.count
DispatchQueue.main.async {
completion(c)
}
}
}
}
PlaygroundPage.current.setLiveView(ContentView())
this funny example demonstrates how to use asynchronous code with SwiftUI