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An easier way to manage sheets in SwiftUI
Jun 6, 2020 swiftui swiftui-presentation

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

TLDR;

If you find this post too long, I have added this to my SwiftUIKit library. You can find the source code here. If you decide to try it out, I’d be very interested in hearing what you think.

The basics

To present sheets in SwiftUI, you use the sheet modifier that takes an isPresented binding and a content function (since this was written, more options have been added):

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 code, state, view builders etc.

I have therefore tried to find a way to handle 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.

Sheet context

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 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.

Presentation context

Since I find that this problem is also true for alerts, modals etc. I have a PresentationContext, which is a small ObservableObject base class with an isActive binding and a generic content view:

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 sheet-specific functions in SheetContext, the context state is properly updated.

Sheet provider

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

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

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

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

Then present these sheets like this:

context.present(AppSheet.settings)

This makes it possible to create plain sheet views or app- and view-specific enums and present all of them in the same way, using the same context.

New sheet modifier

To present sheet, your context must be added to a view. We can do this by wrapping the native sheet modifier in a context-based modifier and provide it with the context state:

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

If you use this modifier instead of the native sheet modifier, you can use the context to present sheets.

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 sheet = SheetContext()

then add a sheet modifier to the view:

.sheet(sheet)

You can now present any views or SheetProviders with the context:

// Present a view
sheet.present(Text("Hello, I'm a custom sheet."))

// Present a sheet provider
sheet.present(AppSheet.settings)

You no longer need multiple @State properties for different sheets or switch over an enum to determine which sheet to show.

Conclusion

SheetContext can be used to present 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 views to present.

Source code

I have added this to my SwiftUIKit library. You can find the source code here. Feel free to try it out and let me know what you think.

An easier way to manage sheets in SwiftUI Jun 6, 2020 swiftuiswiftui-presentation