Atoms
Atoms is a powerful and flexible atomic state management library for Swift, designed to create compact, independent global state components with seamless adaptability and composition.
// Create a text atom
let textAtom = Atom("")
// Create a derived atom that depends on textAtom.
// Atoms automatically update their state when any of their dependencies change.
let extractedNumbersAtom = DerivedAtom {
@UseAtomValue(textAtom) var text
return text.filter {
$0.isNumber
}
}
struct ContentView: View {
// Provide write access to the textAtom
@UseAtom(textAtom) var text
// Provide read-only access to the extractedNumbersAtom
@UseAtomValue(extractedNumbersAtom) var numbers
var body: some View {
VStack {
TextField("", text: $text)
Text("Extracted numbers: \(numbers)")
}
}
}SwiftUI provides great built-in support for handling state, but its object-oriented approach can make code splitting challenging. That's where Atoms can help.
Atoms provide a more granular level of state management, allowing you to focus on what you need without worrying about where to put things. By avoiding large observable objects with many published properties, Atoms help you steer clear of performance bottlenecks due to rendering, while maintaining a single source of truth in your app's architecture.
Atoms comes with 9 different atom types that should cover most of your needs, such as dealing with asyncronousy.
let searchTextAtom = Atom("")
let apiAtom = Atom(...)
// Define a dogsAtom for fetching dogs based on the search text
let dogsAtom = AsyncAtom<[Dog]> {
@UseAtomValue(searchTextAtom, debounce: 0.3) var searchText
@UseAtomValue(apiAtom) var api
return try await api.searchDogs(searchText)
}
struct SearchDogsView: View {
@UseAtom(searchTextAtom) var searchText
@UseAtomValue(dogsAtom) var dogsState
var body: some View {
NavigationStack {
List {
switch dogsState {
case .loading:
ProgressView()
case .success(let dogs):
ForEach(dogs) {
Text($0.name)
}
case .failure(let error):
Text(error.localizedDescription)
Button("Try again") {
dogsAtom.reload()
}
}
}
.searchable(text: $searchText)
}
}
}All atoms that accept a closure as their initial argument will update automatically when their dependencies change.
- Atom: Represents a state for a given value of type
T. - DerivedAtom: A read-only state derived from other atom states.
- AsyncAtom: Manages asynchronous operations that produce a value of type
Tor throw an error, with states represented asAsyncState<T>. - AsyncSequenceAtom: Manages the state of an asynchronous sequence producing values of type
Tor throwing an error, with states represented asAsyncState<T>. - GetSetAtom: Custom getter and setter for values of type
T. - ObservableObjectAtom: Represents a readable state for a given value of type
Tthat conforms toObservableObject. - PublisherAtom: Represents a readable state from a
Publisher, with states represented asAsyncState<T>. - PublishedAtom: Represents a readable state from a
Publishedproperty of typeT. - WillSetAtom: Stores values of type
Tand performs custom logic before updating the stored value.
- UseAtom: Provides read and write access to the atom's value, and it's reactive to changes.
- UseAtomValue: Provides read-only access to the atom's value, and it's reactive to changes.
- CaptureAtom: Captures the atom's value and provides read and write access without being reactive to changes.
- CaptureAtomValue: Captures the atom's value as a constant and provides read-only access without being reactive to changes.
- CaptureAtomPublisher: Provides an
AnyPublisher<T, Never>that emits the current value of the atom and any subsequent updates.
Atoms supports testing and overriding values through dependency injection.
struct SearchDogsView_Previews: PreviewProvider {
static var previews: some View {
SearchDogsView()
.inject(dogsAtom) {
return .success([
.init(name: "Pluto"),
.init(name: "Lassie")
])
}
}
}For testing, one can use the TestStore.
@MainActor
func testDogsSuccess() async throws {
let mock: [Dog] = [.init(name: "Pluto"), .init(name: "Lassie")]
try await TestStore { store in
store.inject(apiAtom) {
.init(searchDogs: { _ in
return mock
})
}
@CaptureAtomValue(dogsAtom) var dogsState: AsyncState<[Dog]>
@CaptureAtom(searchTextAtom) var searchText: String
searchText = "Foo"
try await expectEqual(dogsState, .success(mock))
}
}By default, atom values are stored in memory only while they are actively being used. However, it is still possible to keep certain values alive if needed by passing keepAlive: true when creating an atom.
Atoms can also be used with UIKit in addition to SwiftUI. You can use @CaptureAtomPublisher to subscribe to any atom value changes.
class ViewController: UIViewController {
@CaptureAtomPublisher(searchTextAtom) var searchTextPublisher
private let label = UILabel()
private var cancellable: AnyCancellable?
override func viewDidLoad() {
super.viewDidLoad()
view.addSubview(label)
cancellable = searchTextPublisher
.sink { [weak self] text in
self?.label.text = text
}
}
}If the global namespace is not your thing, you can always create static let properties for scoping.
enum MyAtoms {
static let atom = Atom("")
static let derived = DerivedAtom {
@UseAtomValue(atom) var someValue
return someValue.filter {
$0.isNumber
}
}
}Atoms provides built-in debugging support to help you track state changes. Use the enableAtomLogging method on a View.
Text("Hello, World!")
.enableAtomLogging()Or directly through the AtomStore.
AtomStore.shared.enableAtomLogging(debugScope: .include([counterAtom]))Using property wrappers inline without a following keyword will lead to a compiler error in Xcode < 14.3. The workaround is to either add a semicolon or explicitlly state the type.
let someAtom = DerivedAtom {
@UseAtomValue(someOtherAtom) var value: String
print(value)
return "Hello " + value
}Can be found here
- Open your project in Xcode.
- Go to File > Add Packages....
- In the search bar, enter the URL of the Atoms repository:
https://github.com/bangerang/swift-atoms.git. - Click Add Package.
- Choose the appropriate package options and click Add Package again to confirm.
Atoms comes bundled with AsyncExpectations, which makes writing asynchronous tests easy. Using the TestStore guarantees that your tests run in an isolated context.
@MainActor
func testFilterCompletedTodos() async throws {
try await TestStore { store in
let firstMock = Todo(name: "Todo1")
let secondMock = Todo(name: "Todo2", completed: true)
let mock: [Todo] = [firstMock, secondMock]
store.inject(todosAtom) {
return mock
}
@CaptureAtom(filterTodosOptionAtom) var filterTodosOption: FilterOption
@CaptureAtomValue(filteredTodosAtom) var filteredTodos: [Todo]
filterTodosOption = .completed
try await expectEqual(filteredTodos, [secondMock])
}
}