Open the last used document on App startup

Did you ever want your app to open the last used document on startup? Well, that’s not too difficult on macOS. In your NSDocumentController subclass you have the array of recentDocumentURLs, and on startup you can try to open the first member if it exists.

But on iOS it’s a little bit more tricky. There is no such array as on macOS. So we have to mimic it by ourself.

This is a review of my post 2 years ago: UIDocumentBrowserViewController and External Storage


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.


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.


Performance of a Heavy Multithreading App on Apple Silicon

I couldn’t resist. Now, the new Apple Silicon macs are out and I had to buy a new Mac mini to test my applications on the new architecture (and the new macOS 11.0). Recently I released my refurbished project, the call center simulator CCsim ( It is heavily relying on multithreading and I was eager to see what it is doing on M1-equipped macs. Weiterlesen

Performance of Swift vs. Objective-C and the Debugger

Recently I have migrated an old project of mine from Objective-C to Swift. It was not that difficult and it worked out fine, and I was eager to see how the performance of the migrated system would turn out. How big was my disappointment when I saw that the Swift version of my system was at least a factor of 10 slower than the Objective-C version with unchanged functionality. That can’t be true, I thought and debugged at little bit.