DevAndArtist

// This code uses 3 HIDDEN SwiftUI types, there is no guarantee 
// that it will pass app review, so please use it with caution.
//
//   * SwiftUI._PreferenceValue<Key>
//   * SwiftUI._DelayedPreferenceView<Key, Content>
//   * SwiftUI._PreferenceValue<Key>
//
// Feedback ID for an official support: (FB7577482)
//
// ⚠️ WARNING: 

DevAndArtist

struct PKey: PreferenceKey {
  static var defaultValue: Int?
  static func reduce(value: inout Int?, nextValue: () -> Int?) {
    print(#function, "value:", value as Any, "nextValue:", nextValue() as Any)
    value = nextValue()
  }
}

struct ContentView: View {
  let condition = true

DevAndArtist

// BUG: FB7569572

struct GeometrySizeKey: PreferenceKey {
  static func reduce(value: inout CGSize?, nextValue: () -> CGSize?) {
    value = nextValue()
  }
}

extension View {
  func readGeometrySize() -> some View {

DevAndArtist

import SwiftUI

class Base: CustomDebugStringConvertible {
  var debugDescription: String {
    "\(type(of: self)) \(ObjectIdentifier(self))"
  }

  init() {
    print("🟢 init\t", self)
  }

DevAndArtist

import Combine
import SwiftUI

@available(iOS 13.0, OSX 10.15, tvOS 13.0, watchOS 6.0, *)
@propertyWrapper
public struct Model<Value>: DynamicProperty {
  final class _Box: ObservableObject {
    let objectWillChange = ObservableObjectPublisher()

    var value: Value {

DevAndArtist

import SwiftUI

struct ContentView: View {
  @State var flag = true

  var body: some View {
    let text = "\(flag ? "HStack" : "ZStack")"
    return VStack {
      Text(text)
      Button("change the stack") {

DevAndArtist

fileprivate struct _CompletionPreferenceKey: PreferenceKey {
  typealias Value = CGFloat

  static let defaultValue: CGFloat = 0

  static func reduce(value: inout CGFloat, nextValue: () -> CGFloat) {
    value = nextValue()
  }
}

DevAndArtist

import CoreGraphics

final class TransactionStack {
  static let shared = TransactionStack()
  
  private var _transactions: [Transaction]
  
  private init() {
    dispatchPrecondition(condition: .onQueue(.main))
    _transactions = []

DevAndArtist

import RxSwift
import RxCocoa
import RxRelay

extension Disposable {
  public func wrapIntoAnyDisposable() -> AnyDisposable {
    return AnyDisposable(self)
  }
}

DevAndArtist

WWDC 2019 Labs Questions

Size changes propagation to child view controller

In A Look Inside Presentation Controllers - WWDC 2014 session the following pattern was introduced.

• A child view controller or a presented view controller can issue a request for size update by setting its preferredContentSize property.
• A parent view controller or a presentation controller will receive a callback on preferredContentSizeDidChangeForChildContentContainer method.
• At this point the receiver can decide if can allow the size request and layout the child view controller or the presented view controller.