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State machines enable interactive, logic-driven animations in Rive. They respond to user input, trigger events, and manage complex animation flows automatically.

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Overview

The RiveStateMachineInstance class represents a running instance of a state machine from your Rive file. State machines control animation states based on inputs and conditions, making them ideal for interactive experiences.

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Creating State Machine Instances

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From RiveArtboard

do {
    let file = try RiveFile(name: "button")
    let artboard = try file.artboard()
    
    // Get state machine by name
    let sm = try artboard.stateMachine(fromName: "Button State")
    
    // Get state machine by index
    let firstSM = try artboard.stateMachine(from: 0)
    
    // Get default state machine
    if let defaultSM = artboard.defaultStateMachine() {
        print("Using default state machine")
    }
    
    // List available state machines
    let names = artboard.stateMachineNames()
    print("Available state machines: \(names)")
} catch {
    print("Error loading state machine: \(error)")
}

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Using RiveModel

do {
    let model = try RiveModel(fileName: "button")
    
    // Set state machine by name
    try model.setStateMachine("Button State")
    
    // Set default state machine
    try model.setStateMachine()
    
    // Access the state machine instance
    let sm = model.stateMachine
} catch {
    print("Error setting state machine: \(error)")
}

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Using RiveViewModel

// Create with specific state machine
let viewModel = RiveViewModel(
    fileName: "skills",
    stateMachineName: "Designer's Test"
)

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Advancing State Machines

let sm = try artboard.stateMachine(fromName: "Button State")

// Advance by elapsed time (in seconds)
let deltaTime = 1.0 / 60.0 // 60 FPS
let didStateChange = sm.advance(by: deltaTime)

if didStateChange {
    print("State machine changed state")
}

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Working with Inputs

State machines can have three types of inputs: booleans, numbers, and triggers.

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Accessing Inputs

// Get input count
let count = sm.inputCount()
print("State machine has \(count) inputs")

// List input names
let names = sm.inputNames()
print("Available inputs: \(names)")

// Get input by name
do {
    let input = try sm.input(fromName: "Hover")
} catch {
    print("Input not found")
}

// Get input by index
do {
    let input = try sm.input(from: 0)
} catch {
    print("Input not found")
}

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Boolean Inputs

// Get boolean input
if let boolInput = sm.getBool("isActive") {
    // Read current value
    let currentValue = boolInput.value()
    
    // Set value
    boolInput.value(true)
}

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Number Inputs

// Get number input
if let numberInput = sm.getNumber("Level") {
    // Read current value
    let currentValue = numberInput.value()
    
    // Set value
    numberInput.value(2.5)
}

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Trigger Inputs

// Get trigger input
if let trigger = sm.getTrigger("Reset") {
    // Fire the trigger
    trigger.fire()
}

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Using RiveViewModel for Inputs

let viewModel = RiveViewModel(
    fileName: "skills",
    stateMachineName: "Designer's Test"
)

// Set inputs by name
viewModel.setInput("Level", value: 0.0)  // Beginner
viewModel.setInput("Level", value: 1.0)  // Intermediate
viewModel.setInput("Level", value: 2.0)  // Expert

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State Changes

Track when states change in your state machine: 
// Get number of state changes since last frame
let changeCount = sm.stateChangedCount()

if changeCount > 0 {
    // Get state changes by index
    for i in 0..<changeCount {
        if let state = try? sm.stateChanged(from: i) {
            print("Changed to state: \(state)")
        }
    }
}

// Get all state change names
let changes = sm.stateChanges()
print("States changed: \(changes)")

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Events

Handle events reported by the state machine: 
// Get number of reported events
let eventCount = sm.reportedEventCount()

// Process events
for i in 0..<eventCount {
    let event = sm.reportedEvent(at: i)
    // Handle the event
    print("Event fired: \(event.name())")
}

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Touch/Pointer Interactions

State machines can respond to touch events:

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Basic Touch Events

// Touch began
let hitResult = sm.touchBegan(at: CGPoint(x: 100, y: 100))
if hitResult == .hit {
    print("Touch hit an interactive element")
}

// Touch moved
let moveResult = sm.touchMoved(at: CGPoint(x: 150, y: 150))

// Touch ended
let endResult = sm.touchEnded(at: CGPoint(x: 150, y: 150))

// Touch cancelled
let cancelResult = sm.touchCancelled(at: CGPoint(x: 150, y: 150))

// Touch exited
let exitResult = sm.touchExited(at: CGPoint(x: 200, y: 200))

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Multi-touch Support

Use touch IDs for multi-touch interactions: 
// Touch with ID
let result1 = sm.touchBegan(at: CGPoint(x: 100, y: 100), touchID: 1)
let result2 = sm.touchBegan(at: CGPoint(x: 200, y: 200), touchID: 2)

// Move specific touch
sm.touchMoved(at: CGPoint(x: 150, y: 150), touchID: 1)

// End specific touch
sm.touchEnded(at: CGPoint(x: 150, y: 150), touchID: 1)

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Hit Results

ResultDescription
noneTouch didn’t hit any interactive element
hitTouch hit an interactive element
hitOpaqueTouch hit an opaque interactive element

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Layer Information

// Get number of layers
let layerCount = sm.layerCount()
print("State machine has \(layerCount) layers")

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State Machine Name

let name = sm.name()
print("Running state machine: \(name)")

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Data Binding

Bind view model instances to state machines: 
let file = try RiveFile(name: "animation")
let artboard = try file.artboard()
let sm = try artboard.stateMachine(fromName: "State Machine 1")

if let viewModel = file.defaultViewModel(for: artboard),
   let instance = viewModel.createDefaultInstance() {
    // Bind to state machine (automatically binds to artboard too)
    sm.bind(viewModelInstance: instance)
}

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Complete Example

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SwiftUI State Machine with Inputs

import SwiftUI
import RiveRuntime

struct StateMachineView: View {
    @StateObject private var viewModel = RiveViewModel(
        fileName: "skills",
        stateMachineName: "Designer's Test"
    )
    
    var body: some View {
        VStack {
            viewModel.view()
                .frame(height: 200)
            
            HStack {
                Button("Beginner") {
                    viewModel.setInput("Level", value: 0.0)
                }
                Button("Intermediate") {
                    viewModel.setInput("Level", value: 1.0)
                }
                Button("Expert") {
                    viewModel.setInput("Level", value: 2.0)
                }
            }
        }
    }
}

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Best Practices

State machines are ideal for buttons, toggles, hover effects, and any animation that responds to user input.
let buttonVM = RiveViewModel(
    fileName: "button",
    stateMachineName: "Button State"
)
Always verify inputs exist to avoid runtime errors.
let names = sm.inputNames()
if names.contains("Level") {
    viewModel.setInput("Level", value: 1.0)
}
Process reported events immediately after advancing the state machine to ensure you don’t miss any events.
sm.advance(by: deltaTime)
for i in 0..<sm.reportedEventCount() {
    let event = sm.reportedEvent(at: i)
    handleEvent(event)
}
RiveViewModel provides a simpler API for setting inputs compared to working directly with state machine instances.

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