Creating a macOS document based app with SwiftUI and the new App protocol

Have you already tried to create a macOS document based app with SwiftUI and the new App protocol? Well, there are some problems to solve esp. if you want to use menus focused on the currently open document.

In the old app cycle with AppDelegate / SceneDelegate you still had to use the storyboard to define the menu items and link them to your methods in your document class derived from NSDocument. Enabling and disabling of the menu item according to the open documents was automatically managed by the frameworks.

That’s not the case in the new App protocol of SwiftUI anymore. Instead, you can define your menus and menu items quite nicely in your App struct conforming to the new App protocol but there is no automatic link to the current document in focus.

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SwiftUI Previews: 5s Update Error

Currently, I am developing a quite complex Mac application using Core Data together with SwiftUI. The first challenge I encountered was the SwiftUI preview. I implemented a special preview model with some test data that is assigned to the preview structs of my views as EnvironmentObject. That works fine and I enriched my application step by step.

Well, but suddenly the previews stopped to work. I always got the error message „Updating took more than 5 seconds.“ I suspected one of the recent changes to screw up my work although the completely built applications still worked fine. I walked through my code and certainly found some problematic points but nothing could make the preview show up again.

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