mbrandonw

FB7867609

Consider the following code:

class ViewModel: ObservableObject {
  @Published private(set) var value = 0
}

let vm = ViewModel()

mbrandonw

import SwiftUI

struct ContentView: View {
  @State var isFavorite = false

  var body: some View {
    FavoriteComponent(id: 42, isFavorite: self.$isFavorite)
  }
}

mbrandonw

// This code has a bug. When you try to make a change to the selection
// it will not persist. The `selection` binding is never written to
// no matter what you do in the UI.

import SwiftUI

struct TestView: View {
  @State var selection: Int?

  var body: some View {

mbrandonw

FB7755967

@Published property emits differently in iOS 14 versus iOS 13

The following test fails on iOS 14 but passes in iOS 13:

func testCombineBug() {
  class Store {
    var cancellable: AnyCancellable?
    @Published var count: Int

mbrandonw

FB7746024

Memory leak in Combine when using Concatenate with MergeMany

When you concatenate two publishers, one of which is a merge, you will get a leak reported in Xcode’s memory graph debugger.

The publisher can be as simple as:

self.cancellable = Publishers.Concatenate(
 prefix: Empty(completeImmediately: true),

mbrandonw

The following code sample demonstrates a nested data structure in SwiftUI. You can add rows, drill down into those rows, and then add rows to that child node.

If you drill down 2 levels deep, then tapping “Add row” button no longer updates the UI. But, if you drill out and then drill back in you will see that the rows have appeared.

Paste the following code in a SwiftUI preview to demonstrate:

import SwiftUI

struct NestedState: Equatable, Identifiable {

mbrandonw

FB7673786

Paste the code below into a playground, and try incrementing and decrementing the stepper. The buttons will sporadically enable and disable.

This only happens with the Stepper.init(onIncrement:onDecrement:) initializer. It will work fine with a binding.

import SwiftUI
import PlaygroundSupport

mbrandonw

FB7671513

If you run the code below in a playground you will see that tapping the buttons doesn’t change the UI.

However, if you move the GeometryReader to the outside of ViewModelView it will begin working again.

import SwiftUI
import PlaygroundSupport

mbrandonw

/*

 I expect the following to be printed from running this playground 
 and drilling down to the child view:

 nextIsActive true
 childIsActive false
 ------------
 nextIsActive true
 childIsActive true

mbrandonw

extension Publisher where Failure == Never {
  func promoteError<E>(_ errorType: E.Type = E.self) -> AnyPublisher<Output, E> {
    func never<A>(_ never: Never) -> A {}

    return self
      .mapError(never)
      .eraseToAnyPublisher()
  }
}