How can I present successive views in a SwiftUI-based iOS app? - ios

Question

In attempting to learn SwiftUI, I am working on an iOS app that displays a list view of "observation sessions" and allows users to create new sessions from a "New" button. It requires an intermediate step of selecting a configuration that the new session will be based on.
I am able to show reasonable session list and configuration list screens, but my attempts to handle the selected configuration are failing.
The closure sent to the configurations list screen is called successfully as evidenced by a print statement that correctly displays the configuration name. But the remainder of the handler that is supposed to present a third view type fails to work (i.e. it doesn't present the view). In addition, I am getting a warning where I attempt to present the new view that "Result of call to 'sheet(isPresented:onDismiss:content:)' is unused". I'm hoping somebody can explain to me what I'm doing wrong. This is in Xcode 12.3, targeting iOS 14 in the simulator. Here is the SessionListView code where the problem is exhibited:
import SwiftUI
struct SessionsListView: View {
#ObservedObject var dataManager: DataManager
#State private var isPresented = false
#State private var isObserving = false
var body: some View {
VStack {
List {
ForEach(dataManager.allSavedSessions) {session in
NavigationLink(
// Navigate to a detail view
destination: SessionDetailView(session: session),
label: {
Text("\(session.name)")
})
}
}
Spacer()
Button("New Session") {
isPresented = true
}
.padding()
.font(.headline)
.sheet(isPresented: $isPresented) {
// Present a configuration list view where user must select configuration to use for new session
// Requires a closure that's called upon selection in the configuration list view, to handle the selection
NavigationView {
ConfigurationsListView(dataManager: dataManager, selectionHandler: { config in
isPresented = false
isObserving = true
handleConfigSelection(config)
})
.navigationTitle("Configurations")
.navigationBarItems(trailing: Button("Cancel") {
isPresented = false
})
}
}
}
}
private func handleConfigSelection(_ config: SessionConfiguration) {
// Use the selected configuration to start an observations session
print("Selected \(config.name). Will attempt to show sheet from \(self)")
isPresented = false
isObserving = true
self.sheet(isPresented: $isObserving) { // displaying warning: "Result of call to 'sheet(isPresented:onDismiss:content:)' is unused"
NavigationView {
ObservationsView(configuration: config)
.navigationBarItems(trailing: Button(action: {}) {
Text("Done")
})
}
}
}
}
Here's the code I'm using in this simplified demo for the model types.
ObservationSession:
struct ObservationSession: Identifiable {
let id: UUID = UUID()
let name: String
}
SessionConfiguration:
import Foundation
struct ObservationSession: Identifiable {
let id: UUID = UUID()
let name: String
}
DataManager:
import Foundation
class DataManager: ObservableObject {
var allSavedSessions: [ObservationSession] {
return [ObservationSession(name: "Field mouse droppings"), ObservationSession(name: "Squirrels running up trees"), ObservationSession(name: "Squirrel behavior in urban landscapes")]
}
var allSavedConfigurations: [SessionConfiguration] {
return [SessionConfiguration(name: "Squirrel Behavior"), SessionConfiguration(name: "Squirrel/Tree Interaction"), SessionConfiguration(name: "Mouse Behavior")]
}
}

Answer 1

After a night's sleep I figured out an approach that seems to work.
I added a "currentConfiguration" property to my DataManager class of type SessionConfiguration, and set that property in the ConfigurationsListView when a user selects a configuration from the list. Then the SessionsListView can either present the ConfigurationsListView or an ObservationsView depending on a variable that tracks the flow:
import SwiftUI
enum SessionListPresentationFlow {
case configuration
case observation
}
struct SessionsListView: View {
#ObservedObject var dataManager: DataManager
#State private var isPresented = false
#State var flow: SessionListPresentationFlow = .configuration
var body: some View {
VStack {
List {
ForEach(dataManager.allSavedSessions) {session in
NavigationLink(
// Navigate to a detail view
destination: SessionDetailView(session: session),
label: {
Text("\(session.name)")
})
}
}
Spacer()
Button("New Session") {
isPresented = true
}
.padding()
.font(.headline)
.sheet(isPresented: $isPresented, onDismiss: {
if flow == .observation {
flow = .configuration
} else {
flow = .configuration
}
dataManager.currentConfiguration = nil
isPresented = false
}) {
// Present a view for the appropriate flow
viewForCurrentFlow()
}
}
}
#ViewBuilder private func viewForCurrentFlow() -> some View {
if flow == .configuration {
NavigationView {
ConfigurationsListView(dataManager: dataManager, selectionHandler: { config in
isPresented = false
handleConfigSelection(config)
})
.navigationTitle("Configurations")
.navigationBarItems(trailing: Button("Cancel") {
isPresented = false
flow = .observation
})
}
} else if flow == .observation, let config = dataManager.currentConfiguration {
NavigationView {
ObservationsView(configuration: config)
.navigationBarItems(leading: Button(action: {isPresented = false}) {
Text("Done")
})
}
} else {
EmptyView()
}
}
private func handleConfigSelection(_ config: SessionConfiguration) {
flow = .observation
isPresented = true
}
}