Inspired from a really great Flutter package flutter_bloc this SwiftUI library brings the state management with a BloC (Buisiness logic component) approach to separate views and buisiness logic. With the help of Apple Library "Combine" the state management is handled with the reactive approach.
Requires iOS 13.0+ and MacOS 10.15+
At first you need to decide what approach is more suitable for your app.
If you prefer to make something simple and make changes without depending on what event is currently hapening you could use a Cubit class to create your child cubit and handle state there.
If you would need more complex implementation to track events and map them into states then Bloc class is the choice.
In both scenarios you may also need to create inside your custom View structure a BlocView instance which will accept your newly created cubit/bloc in the initializer and also will require a @ViewBuilder builder function to be provided as well. The idea of the BlocView is to handle rebuilding your views inside the builder callback based on the current state. Whenever the state is changed your view gets rebuild.
You can manipaulate with state as you want. In addition you can also provide to the BlocView constructor a custom action callback which will let you to add some side logic or view behavior without returning any View conforming object.
By default all changes are tracked by a shared instance of BlocObserver and currently only make console printing. You can always set a custom observer for the shared instance and override open methods as you wish.
For convinience you can use a ruby script bloc_template.rb. You need to provide additional parameters for executing the script.
- path
- class_name
- type
Example:
# creates a cubit
ruby bloc_template /MY_PROJECT/MY_CUBIT_FOLDER Counter cubit# creates a bloc
ruby bloc_template /MY_PROJECT/MY_BLOC_FOLDER Counter blocIf you go with Cubit first you need to create a child class. The generic type State can be any type which conforms Equitable protocol.
With the super constructor you can provide the initial state.
In order to emit a new state you need to use emit(state:) method
As a simple example the CounterCubit (the beloved one standar app from Flutter new project)
import SwiftBloc
class CounterCubit: Cubit<Int> {
init() {
super.init(state: 0)
}
func increment() {
emit(state: state + 1)
}
func decrement() {
emit(state: state - 1)
}
}Next you need to use it in your views.
Since our Stategeneric state is Int we can directly access to an integer getter state and display in in the text.
Next, inside your body property create a BlocView with some content:
var body: some View {
BlocView(builder: { (cubit) in
VStack {
Button(action: {
cubit.increment()
}, label: {
Text("Increment")
})
Button(action: {
cubit.decrement()
}, label: {
Text("Decrement")
})
Text("Count: \(cubit.state)")
}
}, cubit: CounterCubit())
}In this case you may use cubit directly from a builder. Moreover this approach will let to use your cubit instance as an @EnvironmentObject so every child view inside your builder function will get the instance of cubit without a need "to drill" through the whole view tree.
If you go with Bloc first you need also to create a child class. The generic types Event and State can be any types which conforms Equitable protocol.
With the super constructor you can provide the initial state.
The difference between Cubit and Bloc although the Bloc is a child class of the Cubit ist the the Bloc uses events to map them into states.
As a simple example the CounterBloc
import SwiftBloc
enum CounterEvent {
case increment
case decrement
}
struct CounterState: Equatable {
let count: Int
func copyWith(count: Int?) -> CounterState {
CounterState(count: count ?? self.count)
}
}
class CounterBloc: Bloc<CounterEvent, CounterState> {
init() {
super.init(initialState: CounterState(count: 0))
}
override func mapEventToState(event: CounterEvent) -> CounterState {
switch event {
case .increment:
return state.copyWith(count: state.count + 1)
case .decrement:
return state.copyWith(count: state.count - 1)
}
}
}The idea is, that everything what is happening in the app are events. Based on that you can call your event as you want, in the example the Enum is used (but you can also use Classes as well, but keep in mind to conform Equatable protocol).
If there are event, then there should be something what will tell about the current app state after the appropriate event.
You need to specify your state model for this. You can also use Classes with inheritance especially if you have some complicated states (and remebemer Equatable)
Now it is time to implement the child Bloc class.
You need to have a constructor where you specify the initial State value.
THE MOST IMPORTANT PART HERE - is to override the mapEventToState(event:) method. Without it nothing will work...
The goal of this method is to transform events to states.
So based on incoming events, the states are generated. You may create new objects of state using CounterState or your can create a method to copy the current state and provide changes to it.
Then the new state will be delivered to your BlocView and your view will be rebuilt automatically!
Now let's see what is the view looks like:
import SwiftBloc
struct BlocContentView: View {
var body: some View {
NavigationView {
BlocView(builder: { (bloc) in
let isPresented = Binding.constant(bloc.state.count < -6)
CounterView()
.alert(isPresented: isPresented) {
Alert(
title: Text("Hi"),
message: Text("Message"),
dismissButton: .cancel {
for _ in 0..<6 {
bloc.add(event: .increment)
}
}
)
}
}, action: { (bloc) in
print(bloc.state.count)
}, base: CounterBloc())
.navigationBarTitle(Text("Bloc"), displayMode: .inline)
}
}
}
struct CounterView: View {
@EnvironmentObject var bloc: CounterBloc
var body: some View {
if bloc.state.count > 5 {
LimitView()
} else {
OperationView()
}
}
}
struct LimitView: View {
@EnvironmentObject var bloc: CounterBloc
var body: some View {
VStack {
Text("Hooora")
Button(action: {
for _ in 0..<6 {
bloc.add(event: .decrement)
}
}, label: {
Text("Reset")
})
}
}
}
struct OperationView: View {
@EnvironmentObject var bloc: CounterBloc
var body: some View {
VStack {
Button(action: {
bloc.add(event: .increment)
}, label: {
Text("Send Increment event")
})
Button(action: {
bloc.add(event: .decrement)
}, label: {
Text("Send Decrement event")
})
Text("Count: \(bloc.state.count)")
}
}
}The Bloc class is monitoring the changes of the event property via @PublishedSubject property wrapper. This bloc instance is set by default as @EnvironmentObject and will be available for all child views if needed.
You may want to test your Blocs to be sure that the awaited states are actually happening if appropriate events passed in.
BlocTest.execute will expect to have four callbacks:
- build (create a Bloc instance inside the closure)
- act (provide a sequence of events)
- expect (set awaited states)
- verify (handle information about equality of expected and real states)
final class SwiftBlocTests: XCTestCase {
func testCounterBlocInitial() {
BlocTest.execute(build: {
MockCounterBloc()
}, act: { (_) in
// DO NOTHING
}, expect: {
[
MockCounterState(count: 0)
]
}, verify: { areEqual, message in
XCTAssert(areEqual, message)
})
}
func testCounterBlocIncrement() {
BlocTest.execute(build: {
MockCounterBloc()
}, act: { (bloc) in
bloc.add(event: .increment)
bloc.add(event: .increment)
}, expect: {
[
MockCounterState(count: 0),
MockCounterState(count: 1),
MockCounterState(count: 2)
]
}, verify: { areEqual, message in
XCTAssert(areEqual, message)
})
}
func testCounterBlocDecrement() {
BlocTest.execute(build: {
MockCounterBloc()
}, act: { (bloc) in
bloc.add(event: .decrement)
bloc.add(event: .decrement)
}, wait: 3.0, expect: {
[
MockCounterState(count: 0),
MockCounterState(count: -1),
MockCounterState(count: -2)
]
}, verify: { areEqual, message in
XCTAssert(areEqual, message)
})
}
} To run the example project, clone the repo, and run pod install from the Example directory first.
The library supports iOS 13 & above.
SwiftBloc is available through CocoaPods. To install it, simply add the following line to your Podfile:
pod 'SwiftBloc'or
pod 'SwiftBloc', '~> 1.0.3'To install it, simply add the following lines to your Package.swift file (or just use the Package Manager from within XCode and reference this repo):
dependencies: [
.package(url: "https://github.com/VictorKachalov/SwiftBloc.git", from: "1.0.3")
]Add the line in your cartfile
github "VictorKachalov/SwiftBloc" "1.0.3"Victor Kachalov, victorkachalov@gmail.com
SwiftBloc is available under the MIT license. See the LICENSE file for more info.
If you think that my repo helped you to solve the issues you struggle with, please don't be shy and sponsor :-)