SwiftUI macOS Commands (menu bar) and View - swift

Question

Hi I am starting to learn SwiftUI and macOS development. I am using the SwiftUI life cycle. How do I call a function from the focused window from the menu bar.
Besides Apple documentation, I found this reference and am able to create menu items using Commands but I have no idea how to call a function from my view.
For example:
Suppose this is my App struct:
import SwiftUI
#main
struct ExampleApp: App {
var body: some Scene {
WindowGroup {
ContentView()
}
}.commands {
CommandMenu("First menu") {
Button("Action!") {
// How do I call the views action function?
}
}
}
}
and this is my View:
struct ContentView: View {
public func action() {
print("It works")
}
var body: some View {
Text("Example")
}
}
I just typed the example code sorry if there are any typos but I hope you can get the idea.

Answer 1

Because Views in SwiftUI are transient, you can't hold a reference to a specific instance of ContentView to call a function on it. What you can do, though, is change part of your state that gets passed down to the content view.
For example:
#main
struct ExampleApp: App {
#StateObject var appState = AppState()
var body: some Scene {
WindowGroup {
ContentView(appState: appState)
.frame(maxWidth: .infinity, maxHeight: .infinity)
}.commands {
CommandMenu("First menu") {
Button("Action!") {
appState.textToDisplay = "\(Date())"
}
}
}
}
}
class AppState : ObservableObject {
#Published var textToDisplay = "(not clicked yet)"
}
struct ContentView: View {
#ObservedObject var appState : AppState
var body: some View {
Text(appState.textToDisplay)
}
}
Note that the .commands modifier goes on WindowGroup { }
In this example, AppState is an ObservableObject that holds some state of the app. It's passed through to ContentView using a parameter. You could also pass it via an Environment Object (https://www.hackingwithswift.com/quick-start/swiftui/how-to-use-environmentobject-to-share-data-between-views)
When the menu item is clicked, it sets textToDisplay which is a #Published property on AppState. ContentView will get updated any time a #Published property of AppState gets updated.
This is the general idea of the pattern you'd use. If you have a use case that isn't covered by this pattern, let me know in the comments.
Updates, based on your comments:
import SwiftUI
import Combine
#main
struct ExampleApp: App {
#StateObject var appState = AppState()
var body: some Scene {
WindowGroup {
ContentView(appState: appState)
.frame(maxWidth: .infinity, maxHeight: .infinity)
}.commands {
CommandMenu("First menu") {
Button("Action!") {
appState.textToDisplay = "\(Date())"
}
Button("Change background color") {
appState.contentBackgroundColor = Color.green
}
Button("Toggle view") {
appState.viewShown.toggle()
}
Button("CustomCopy") {
appState.customCopy.send()
}
}
}
}
}
class AppState : ObservableObject {
#Published var textToDisplay = "(not clicked yet)"
#Published var contentBackgroundColor = Color.clear
#Published var viewShown = true
var customCopy = PassthroughSubject<Void,Never>()
}
class ViewModel : ObservableObject {
#Published var text = "The text I have here"
var cancellable : AnyCancellable?
func connect(withAppState appState: AppState) {
cancellable = appState.customCopy.sink(receiveValue: { _ in
print("Do custom copy based on my state: \(self.text) or call a function")
})
}
}
struct ContentView: View {
#ObservedObject var appState : AppState
#State var text = "The text I have here"
#StateObject private var viewModel = ViewModel()
var body: some View {
VStack {
Text(appState.textToDisplay)
.background(appState.contentBackgroundColor)
if appState.viewShown {
Text("Shown?")
}
}
.onReceive(appState.$textToDisplay) { (newText) in
print("Got new text: \(newText)")
}
.onAppear {
viewModel.connect(withAppState: appState)
}
}
}
In my updates, you can see that I've addressed the question of the background color, showing hiding a view, and even getting a notification (via onReceive) when one of the #Published properties changes.
You can also see how I use a custom publisher (customCopy) to pass along an action to ContentView's ViewModel