【SwiftUI】ScrollView + LazyVStack vs Large amounts of data 👉 https://android.benigumo.com/20240627/scrollview-lazyvstack-vs-large-amounts-of-data/

LargeData.swift

import SwiftUI
import SwiftData

@MainActor @Observable
final class LargeData {
  var loadedItems: [Item] = []
  var count = 0

  private var modelContext: ModelContext!
  private var predicate: Predicate<Item>!
  private var page = 0

  private let limit = 1000

  func setContext(modelContext: ModelContext) {
    self.modelContext = modelContext
  }

  func find(contains: String) {
    predicate = .predicateItems(text: contains)
    count = (
      try? modelContext.fetchCount(.fetchItems(predicate: predicate))
    ) ?? 0

    page = 0
    loadedItems.removeAll()
    fetchPage()
  }

  func next() {
    if count > (page + 1) * limit {
      page += 1
      fetchPage()
    }
  }

  private func fetchPage() {
    loadedItems.append(
      contentsOf: (
        try? modelContext.fetch(
          .fetchItems(predicate: predicate, offset: page * limit, limit: limit)
        )
      ) ?? []
    )
  }
}

fileprivate extension Predicate {
  static func predicateItems(text: String) -> Predicate<Item> {
    return #Predicate { text.isEmpty || $0.s.contains(text) }
  }
}

fileprivate extension FetchDescriptor {
  static func fetchItems(
    predicate: Predicate<Item>, offset: Int = 0, limit: Int? = nil) -> FetchDescriptor<Item> {
      var descriptor = FetchDescriptor<Item>(predicate: predicate,  sortBy: [.init(\.i)])
      descriptor.fetchOffset = offset
      descriptor.fetchLimit = limit
      return descriptor
    }
}