An easier way to manage sheets in SwiftUI

Jun 6, 2020
#swift #swiftui

In this post, we’ll look at an easier way to manage sheets in SwiftUI, that lets us reuse functionality, reduce state management and present many different sheets in the same way.

TLDR;

If you find this post too long, I have added this to my SwiftUIKit library. You can find the source code here and checkout the demo app for a fully working example.

The basics

To present sheets in SwiftUI, you use the sheet modifier that takes an isPresented binding and a content function:

struct MyView: View {
    
    @State private var isSheetActive = false
    
    var body: some View {
        Button("Show sheet", action: showSheet)
            .sheet(isPresented: $isSheetActive, content: sheetContent)
    }
    
    func sheetContent() -> some View {
        Text("Hello, world!")
    }

    func showSheet() {
        isSheetActive = true
    }
}

This can become tricky when you have to present multiple sheets from the same screen or reuse sheets across an app. You may end up duplicating state and view builder logic and having to write the same code many times.

I therefore tried to find a way to work with sheets in a more reusable way, that requires less code and less state while still being flexible to support both global and screen-specific sheets.

It all begins with a very simple state manager that I call SheetContext.

SheetContext

Instead of managing state in every view that should present sheets, I use a SheetContext:

public class SheetContext: PresentationContext<AnyView> {
    
    public override func content() -> AnyView {
        contentView ?? EmptyView().any()
    }
    
    public func present<Sheet: View>(_ sheet: Sheet) {
        present(sheet.any())
    }
    
    public func present(_ provider: SheetProvider) {
        contentView = provider.sheet
    }
}

As you can see, it basically only contains code for presenting a Sheet (which is just a view) or a SheetProvider. We’ll come back to the provider shortly.

You may also notice that it inherits something called PresentationContext. Let’s take a closer look at this base class.

PresentationContext

Since I find that the sheet presentation problem also is true for alerts, toasts etc., I have a PresentationContext, which is a pretty simple ObservableObject base class:

public class PresentationContext<Content>: ObservableObject {
    
    public init() {}
    
    @Published public var isActive = false
    
    public var isActiveBinding: Binding<Bool> {
        .init(get: { self.isActive },
              set: { self.isActive = $0 }
        )
    }
    
    open func content() -> Content { contentView! }
    
    public internal(set) var contentView: Content? {
        didSet { isActive = contentView != nil }
    }
    
    public func dismiss() {
        isActive = false
    }
    
    public func present(_ content: Content) {
        contentView = content
    }
}

By calling the more specific functions in SheetContext, the PresentationContext state is properly updated.

SheetProvider

As we saw earlier, SheetContext can present a Sheet and a SheetProvider. Sheet is just a view, while SheetProvider is a protocol for anything that can provide a sheet view:

public protocol SheetProvider {
    
    var sheet: AnyView { get }
}

With this in place, you can now implement custom sheets in many different ways and present all of them the same way, using this new context.

For instance, you can have an enum that represents the various sheets your app supports:

enum AppSheet: SheetProvider {
    
    case settings, tutorial
    
    var sheet: AnyView {
        switch self {
        case .settings: return SettingsScreen().any()
        case .tutorial: return TutorialScreen().any()
        }
    }
}

This makes it possible to create app and view specific enums that contain your app’s sheet logic, which can all be presented in the same way.

New sheet modifier

In SwiftUI, you present sheets by adding a modifier to the presenting view. With the new SheetContext managing our state, we can create a new sheet modifier:

public extension View {
    
    func sheet(context: SheetContext) -> some View {
        sheet(isPresented: context.isActiveBinding, content: context.content)
    }
}

The new modifier just provides the standard sheet modifier with the context’s state, which makes things easier for you.

Presenting a sheet

With these new tools at our disposal, we can present sheets in a much easier way. First, create a context property:

@StateObject private var sheetContext = SheetContext()

then add a sheet modifier to the view:

.sheet(context: sheetContext)

You can now present any SheetProvider as a sheet, for instance AppSheet:

sheetContext.present(AppSheet.settings)

You can also present any custom view in the same way, using the same context:

sheetContext.present(Text("Hello, I'm a custom sheet."))

That’s it, your view don’t need multiple @State properties for different sheets or to switch over an enum to determine which sheet to show.

@StateObject vs @ObservedObject

Use @StateObject for your contexts whenever possible. However, if you target iOS 13 or if the context is created and managed by another part of your app, use @ObservedObject.

Conclusion

As you can see, SheetContext can be used to manage all different kind of views. It manages all state for you and lets you use a more convenient modifier. All you have to do is provide it with the sheet you want to present.

Source code

I have added these components to my SwiftUIKit library. You can find the source code here.