Changable themes in SwiftUI

ContentView.swift

import SwiftUI

struct Theme: Hashable {
    var colorPrimary: Color = Color.primary
    var name: String? = nil
    var publicName: String = "System"
}

var themes: [Theme] = [
    Theme(colorPrimary: Color.primary, name: nil, publicName: "System"),
    Theme(colorPrimary: Color.purple, name: "purple", publicName: "Purple"),
    Theme(colorPrimary: Color.orange, name: "orange", publicName: "Orange"),
    Theme(colorPrimary: Color.red, name: "red", publicName: "Red"),
    Theme(colorPrimary: Color.green, name: "green", publicName: "Green"),
    Theme(colorPrimary: Color.blue, name: "blue", publicName: "Blue"),
    Theme(colorPrimary: Color.pink, name: "pink", publicName: "Pink"),
    Theme(colorPrimary: Color.yellow, name: "yellow", publicName: "Yellow"),
]

func getTheme(themeName: String?) -> Theme {
    if themeName != nil {
        for theme in themes {
            if themeName! == theme.name {
                return theme
            }
        }
    }
    return themes[0]
}

func getCurrentTheme() -> Theme {
    let currentThemeName = UserDefaults.standard.string(forKey: "themeName")
    return getTheme(themeName: currentThemeName)
}

struct ChangeThemeButton: View {
    @Binding var currentThemeName: String?
    var colorName: String
    var themeName: String?
    
    var body: some View {
        HStack {
            Button(action: {
                UserDefaults.standard.set(self.themeName, forKey: "themeName")
                self.currentThemeName = UserDefaults.standard.string(forKey: "themeName")
                NotificationCenter.default.post(name: NSNotification.Name(rawValue: "themeUpdated"), object: self)
            }) {
                HStack {
                    Circle()
                    .fill(getTheme(themeName: themeName).colorPrimary)
                    .frame(width: 25, height: 25)
                    
                    Text(self.colorName)
                    
                    if self.currentThemeName == themeName {
                        Image(systemName: "checkmark")
                    }
                }
            }
        }
    }
}

struct SelectThemeView: View {
    @State var currentThemeName = UserDefaults.standard.string(forKey: "themeName")
    
    var body: some View {
        List {
            ForEach(themes, id: \.self) { theme in
                ChangeThemeButton(currentThemeName: self.$currentThemeName, colorName: theme.publicName, themeName: theme.name)
            }
        }
        .navigationBarTitle("Theme").onAppear {
            self.currentThemeName = UserDefaults.standard.string(forKey: "themeName")
        }
    }
}

struct SettingsView: View {
    var body: some View {
        NavigationView {
            List {
                NavigationLink(destination: SelectThemeView()) {
                    Text("Change theme")
                }
            }
            .navigationBarTitle("Settings")
        }
    }
}

struct ContentView: View {
  @State var currentTheme: Theme = getCurrentTheme()
  @State private var selection = 0
  
  var body: some View {
    HStack {
      TabView(selection: $selection){
        Text("Hello, world!")
          .tabItem {
            VStack {
                Image(systemName: "folder")
                Text("Hello")
            }
          }
          .tag(0)
        SettingsView()
          .tabItem {
            VStack {
                Image(systemName: "gear")
                Text("Settings")
            }
          }
          .tag(1)
      }
    }
    .accentColor(currentTheme.colorPrimary)
    .onAppear {
        NotificationCenter.default.addObserver(forName: NSNotification.Name(rawValue: "themeUpdated"), object: nil , queue: nil) { (notification) in
            DispatchQueue.main.async {
                self.currentTheme = getCurrentTheme()
            }
        }
    }
  }
}
  

this is great code to build off of. thanks!

this is great code to build off of. thanks!

Thank you!