In my last post I talked about some of the struggles I'm having getting up to speed with SwiftUI. Let's dive in to a couple of examples.

Magic Environments

To make my Settings form view, I found a suer helpful blog post by Majid Jabrayilov where he goes over the basics of building a Form with SwiftUI and binding some controls to UserDefaults. He outlines a type called SettingsStore, which I also implemented. I diverged from the tutorial to try my hand at making a property wrapper type to handle fetching from and saving to UserDefaults. When it came time to wire a switch up with its associated value is where I slowed quite a bit. The post has this line of code in the SettingsView type:

@EnvironmentObject var settings: SettingsStore

What this says is that somewhere in the SwiftUI environment will be a SettingsStore instance. What's missed in the post is how the thing gets there in the first place. It turns out that an ancestor of my SettingsView needs to inject the property into the environment when also constructing the view. Here's what that looks like in Scorebook's case, where the SettingsView is visible as a tab item in the tab bar.

let hostingController = UIHostingController(rootView: SettingsListView().environmentObject(SettingsStore()))

So after putting my SettingsView inside of the UIHostingController, I also need to chain an environmentObject(_:) call to put the store in the environment. When I failed to do this at first I got a crash, and when I tried constructing the environment and passing it in via constructor injection I couldn't set the variable. It has to be done through the environment. For my taste, it's feeling a bit magic-y at the moment but I'm hopeful that's due to the fact that I don't know what I'm doing very well just yet.

Conditional View Navigation

I've got a button on my settings screen to send me an email. In UIKit land I have an action on the button and check that the device in question can send the email, then it presents the mail compose screen. If it cannot, then I show an alert. Easy enough.

But in SwiftUI land it's not so easy (at least to my imperatively wired mind). Thankfully I found a helpful StackOverflow question to help me get started with sending the message. I honestly don't quite understand exactly how the UIViewControllerRepresentable protocol works yet but I think the code in that answer gives me a good starting point. One thing that is kind of breaking my Objective-C brain is the usage of _ when setting the initial value of a @Binding property. It's like setting the instance variable used to be in days of old.

The trouble comes in triggering the mail view from my settings screen. I think I've gotten it working with a dual-boolean option (again, somehow managed via magic). Here's what I've come up with (and this is working-ish in the simulator):

struct SettingsListView: View {
    // Mail
    @State var mailResult: MailResult?
    @State var isShowingMailView = false
    @State var isShowingMailErrorAlert = false

    var body: some View {
        NavigationView {
                Section(header: Text("Feedback".uppercased())) {
                    Button(action: {
                        if MFMailComposeViewController.canSendMail() {
                            self.isShowingMailView.toggle()
                        }
                        else {
                            self.isShowingMailErrorAlert.toggle()
                        }
                    }) {
                        Text("Send Email")
                    }
                }
            }
            .navigationBarTitle(Text("Settings"))
            .alert(isPresented: $isShowingMailErrorAlert) {
                Alert(title: Text("Unable to send mail"),
                      message: nil,
                      dismissButton: .default(Text("OK")))
            }

            if isShowingMailView {
                MailView(isShowing: $isShowingMailView, result: $mailResult)
                    .transition(.move(edge: .bottom))
                    .animation(.default)
            }
        }
        .navigationViewStyle(StackNavigationViewStyle())
    }
}

I haven't tried this on a device yet as I haven't installed iOS 13 at this point on anything (those days are nearing an end) but the Alert at least shows in the simulator. What I find kind of gross about this is the fact that I have separate @State booleans for showing or presenting content. How do those get reset when I dismiss the things they're presenting? It sounds like SwiftUI handles that but I don't know how.

I also don't like taking what was one single method in my UIKit code and scattering its pieces in a declarative spew of state all around my view code. I'm hoping there's a nice, Combine-y way of doing this that can let me isolate the states in clearer fashion.

Lots to learn still, which makes this exciting and frustrating all at the same time!