SwiftMVI/Documentation/Getting_Started.md

Getting started

To build a ui feature using the SwiftMVI you define some types and values that model your domain:

• ImmutableState: An integer as the state of your UI.
• Intent: A type that represents all of the user actions that can happen in your feature.
• IntentReducer: A function that handles intents and processes them over time.
• Processing: Enable processing functionalities in a feature.

As a basic example, consider a UI that shows a number along with + and − buttons that increment and decrement the number.

Here we need to define a type for the feature's state, which consists of an integer for the current count:

import SwiftMVI

class Feature: ObservableObject, ImmutableState {
    var state = 0
}

We also need to define a type for the feature's intents, there are two intents one for the increase and one for decrease:

extension Feature: IntentReducer {
    enum Intent {
        case increment
        case decrement
    }
}

And then we implement the reduce method which is responsible for handling the behaviour of the feature. In this example to change the state we need to add Processing protocol and call .state:

extension Feature: IntentReducer, Processing {
    enum Intent { ... }
    func reduce(intent: Intent) {
        switch intent {
        case .increment:
            state {
                $0 += 1
            }
        case .decrement:
            state {
                $0 -= 1
            }
        }
    }
}

And then finally we define the view that displays the feature, adding as StateObject or ObservedObject and call by passing its Intent:

struct FeatureView: View {
    @StateObject var feature = Feature()
    
    var body: some View {
        VStack {
            HStack {
                Button("−") { feature(.decrement) }
                Text("\(feature.state)")
                Button("+") { feature(.increment) }
            }
        }
    }
}