⚡️ OptimizedVStack

A high-performance vertical stack implementation for list-style layouts in SwiftUI.
An alternative to the standard LazyVStack and List, focused on correct layout, improved hitch rate/RAM usage and fine-grained control.

🚀 Additional Features

• 📐 Access to container content size information (without using GeometryReader or the protocol Layout)
• 🧹 No size's information "spam" to client
• ✅ Correct layout. No "white" flaky screens, no content truncating
• 🪵 Improved cell's rendering OSLogging quality
• ⚡️ Enhanced memory usage performance

⚡ Quick Start

1. 📥 Clone the repository
2. 🧩 Write a bit of code and build the project

        OptimizedVStack(
            data: $viewModel.items,
            spacing: 8,
            onChangeOfHeight: {
                print($0.formatted)
            }
        ) { index in
            CellView(by: $viewModel.items[index])
        }

3. 👀 Observe the height value in the console

👉 Alternatively, you can open the Demo/Screen folder and modify any of the prototypes as you like.

🧩 Supported Scenarios

• Fixed row height lists
• Variable row height lists
• Dynamic row height lists
• List pagination

The simplest initialization looks like this:

      OptimizedVStack(
          data: items
      ) { index in
          CellView(by: items[index])
      }

• For the "scroll progress tracking" case, the following API is used in the Demo app:

  ProgressLine(...)
  OptimizedVStack(
      data: $viewModel.items,
      spacing: 8,
      onChangeOfScrollProgress: { currentYMax, measuredheight in
          let totalHeight = switch measuredheight {
          case .exact(let total), .estimated(let total, _, _):
              total
          default:
              CGFloat.zero
          }
                    
          viewModel.updateScrollProgress(
            currentYMax: currentYMax, totalHeight: totalHeight
          )
      },
      rowContent: { index in
          CellView(by: viewModel.items[index])
      },
      footer: {
          loader
      }
  )

• For the "pagination" use case, the following API is used in the Demo app:

  OptimizedVStack(
      data: $viewModel.items,
      spacing: 8,
      onChangeOfHeight: {
          print($0.formatted)
      },
      rowContent: { index in
          CellView(by: viewModel.items[index])
      },
      footer: {
          loader
      }
  )

🪵 Logs

The implementation sends content setup logs via OSLog.
Inspired by the native LazyVStack logs, enabled through the UserDefaults key: com.apple.SwiftUI.LazyStackLogging.

⏱ Benchmark:

Actual content height: 1086
Tested: iOS 26
Test's scheme: link

Approach	Result	Final Height	Iterations	API Notes
List + GeometryReader	-	778	-	iOS 13+
List + Introspect + uiCollectionView.contentSize	-	803	-	iOS 13+
LazyVStack + GeometryReader	+	1086	5	iOS 14+
LazyVStack + ViewThatFits	+	1086	5	iOS 16.4+
LazyVStack + View.scrollBounceBehavior	+	1086	2	iOS 16.4+
OptimizedVStack + onChangeOfHeight	+	1086	1	iOS 14+

First's frame layout speed
iPhone 12, iOS 18.6.2
Test's scheme: link

Approach	Result
LazyVStack	25 ms.
OptimizedVStack	10 ms.

Hitch test (dragging the scroll indicator for fast scrolling in 30 seconds)
iPhone 12, iOS 18.6.2
Test's scheme: link

Approach	Hitch time	Max hitch
LazyVStack	610 ms.	80 ms.
List	3.5 s.	75 ms.
OptimizedVStack	315 ms.	70 ms.

Peak RAM usage (dragging the scroll indicator for fast scrolling in 30 seconds)
iPhone 12, iOS 18.6.2
Test's scheme: link

Approach	Result
LazyVStack	24.5 MB.
List	26 MB.
OptimizedVStack	21.0 MB.

🚀 Very fast! 🚀

📦 Dependencies:

• Only standard iOS SDK (Foundation, SwiftUI, UIKit, os)

📄 License

Source code is released under the Apache License 2.0. See LICENSE for details.