Presenting SwiftUI views from DocumentGroup
May 16, 2022 ·
The SwiftUI DocumentGroup makes it easy to create document-based apps. However, it is a bit limited, with some basic things being hard to do. In this post, let’s take a look at how we can present custom views as modals from a DocumentGroup.
Background
When you create a DocumentGroup-based app for the first time, you may be surprised by how easy it is to get started. Just provide the DocumentGroup with the view you want to use to present documents with, and you’re good to go. Kind of.
The DocumentGroup takes a regular SwiftUI view, which means that we can use standard SwiftUI components like toolbars, navigation views, sheets, etc. to create a powerful app.
However, while DocumentGroup is easy to use, it’s also pretty limited in functionality. There is very little you can customize with the public api:s, which means that you will have to do some UIKit/AppKit hacking to get even the most basic thing to work.
For instance, say that you want to present a sheet from a document group, e.g. to show an onboarding when the user first opens the app. This is not possible, since DocumentGroup is not a view. You only get a view once you open a document, which may be too late.
Solution
We can work around this limitation by dropping down to UIKit & AppKit and use the more extensive api:s that these frameworks provide.
Let’s build a UIKit-specific workaround by first defining a DocumentGroupSheet protocol that can be implemented by any SwiftUI view:
public protocol DocumentGroupSheet: View {}
Let’s also define a specific error for things that can go wrong when doing this workaround:
public enum DocumentGroupSheetError: Error {
case noParentWindow
}
We can now extend DocumentGroupSheet to make it present itself from any DocumentGroup:
public extension DocumentGroupSheet {
func presentFromDocumentGroup() throws {
let window = UIApplication.shared.activeKeyWindows.first
let parent = window?.rootViewController
guard let parent = parent else { throw DocumentGroupSheetError.noParentWindow }
let sheet = UIHostingController(rootView: body)
parent.present(sheet, animated: true, completion: nil)
}
}
This workaround is pretty basic, and doesn’t even require the active view controller to be a document group. We try to get the active root view controller, and throw an error if none exists. We then create a hosting controller with the view body and present it as a sheet.
With this, views can either present themselves by calling the present function from within the view. We can also let the app create a view instance and present it whenever we want.
Conclusion
The SwiftUI DocumentGroup is limited, but we can easily extend the available functionality by using UIKit & AppKit. This will hopefully not be needed in future versions of SwiftUI.
You can find the source code in my SwiftUIKit library. Don’t hesitate to comment or reach out with any thoughts you may have.
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