State Machines and Input-Driven Motion
Wire Rive state machine inputs to app data for reactive, branching animations.
State Machines and Input-Driven Motion is a free Flutter Mobile Development lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Flutter Mobile Development learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Why State Machines Beat Linear Animations
Traditional Rive animations play a single timeline from start to finish. A state machine is a graph of animation states connected by transitions, and those transitions fire based on inputs you control from Dart.
- Reactive: the animation reflects live app data instead of a fixed sequence.
- Branching: the same artboard can idle, hover, succeed, or fail depending on input values.
- Blended: Rive interpolates between states, so you get smooth motion for free.
In this lesson you will wire a Rive state machine's inputs to your widget tree so motion follows user actions and model state.
The Three Input Types
A Rive state machine exposes exactly three input kinds, and choosing the right one is the core design decision.
- Boolean (
SMIBool): a held on/off value, e.g.isOpenorisLoading. - Number (
SMINumber): a continuous value that can drive blend states, e.g. a 0–100 progress or a scroll offset. - Trigger (
SMITrigger): a one-shot pulse that fires a transition once, e.g.tapSuccess. It has no persistent value.
Rule of thumb: use a Trigger for momentary events, a Boolean for state you hold, and a Number for anything continuous you want to blend.
Loading the Artboard and State Machine
To drive inputs you need a StateMachineController. The onInit callback of RiveAnimation.asset hands you the loaded Artboard. You build a controller from a named state machine and attach it.
Always grab references to the inputs you need right here, while you still have the artboard, and store them on your widget's state.
import 'package:flutter/material.dart';
import 'package:rive/rive.dart';
class LikeButton extends StatefulWidget {
const LikeButton({super.key});
@override
State<LikeButton> createState() => _LikeButtonState();
}
class _LikeButtonState extends State<LikeButton> {
StateMachineController? _controller;
SMIBool? _isLiked;
void _onRiveInit(Artboard artboard) {
final controller = StateMachineController.fromArtboard(
artboard,
'LikeMachine',
);
if (controller != null) {
artboard.addController(controller);
_controller = controller;
_isLiked = controller.findInput<bool>('isLiked') as SMIBool?;
}
}
@override
Widget build(BuildContext context) {
return RiveAnimation.asset(
'assets/like.riv',
stateMachines: const ['LikeMachine'],
onInit: _onRiveInit,
);
}
}Setting a Boolean Input from a Tap
Once you hold an SMIBool reference, driving it is just assigning to its value. Rive immediately evaluates transitions whose condition depends on that input.
Wrap the Rive widget in a GestureDetector and toggle the boolean. There is no need to call setState for the animation itself — Rive repaints internally — but you may want it to keep your own model in sync.
GestureDetector(
onTap: () {
final input = _isLiked;
if (input != null) {
input.value = !input.value; // flips the held state
}
},
child: RiveAnimation.asset(
'assets/like.riv',
stateMachines: const ['LikeMachine'],
onInit: _onRiveInit,
),
)Firing a Trigger for One-Shot Motion
A SMITrigger has no value. You call fire() to pulse it exactly once, which is perfect for confetti bursts, success checkmarks, or shake-on-error feedback.
Because triggers auto-reset, you never have to clear them. Firing again replays the transition.
class _SubmitButtonState extends State<SubmitButton> {
SMITrigger? _success;
SMITrigger? _error;
void _onInit(Artboard artboard) {
final c = StateMachineController.fromArtboard(artboard, 'SubmitMachine');
if (c != null) {
artboard.addController(c);
_success = c.findSMI('success') as SMITrigger?;
_error = c.findSMI('error') as SMITrigger?;
}
}
Future<void> _onSubmit() async {
final ok = await _saveForm();
if (ok) {
_success?.fire();
} else {
_error?.fire();
}
}
}Driving a Number Input for Blended States
Number inputs shine when motion must follow a continuous value. A blend state in Rive can morph an artboard across a 0–100 range, so feeding it live data produces fluid, data-driven motion.
Common sources: download progress, a scroll position, a slider, or a sensor reading. Clamp the value so it never exceeds the range the artist designed for.
class _ProgressGaugeState extends State<ProgressGauge> {
SMINumber? _progress;
void _onInit(Artboard artboard) {
final c = StateMachineController.fromArtboard(artboard, 'GaugeMachine');
if (c != null) {
artboard.addController(c);
_progress = c.findSMI('progress') as SMINumber?;
}
}
void updateProgress(double fraction) {
// fraction is 0.0..1.0 from a download stream
_progress?.value = (fraction * 100).clamp(0, 100);
}
}Connecting Inputs to a Stream of App Data
Input-driven motion becomes powerful when a data stream feeds it. Subscribe in initState, push each event into the matching input, and cancel the subscription in dispose to avoid leaks.
Notice you guard against a null input: the stream may emit before onInit has run, so a null-aware call keeps you safe.
late final StreamSubscription<double> _sub;
@override
void initState() {
super.initState();
_sub = downloadProgress$.listen((fraction) {
_progress?.value = (fraction * 100).clamp(0, 100);
});
}
@override
void dispose() {
_sub.cancel();
_controller?.dispose();
super.dispose();
}Modeling Branching Logic in Pure Dart
Before touching Rive, it helps to model the decision that selects a branch as plain Dart. Here is a self-contained mapper that turns an upload result into the kind of input event you would fire. Testing this logic in isolation keeps your widget thin.
This snippet has no Flutter or Rive dependency, so it runs anywhere.
enum MotionEvent { idle, loading, success, error }
MotionEvent selectMotion({
required bool inFlight,
required bool? succeeded,
}) {
if (inFlight) return MotionEvent.loading;
if (succeeded == null) return MotionEvent.idle;
return succeeded ? MotionEvent.success : MotionEvent.error;
}
void main() {
print(selectMotion(inFlight: true, succeeded: null)); // loading
print(selectMotion(inFlight: false, succeeded: true)); // success
print(selectMotion(inFlight: false, succeeded: false)); // error
print(selectMotion(inFlight: false, succeeded: null)); // idle
}Applying a Branch Decision to Inputs
Now bind that pure decision to the state machine. A single method translates a MotionEvent into the correct combination of boolean holds and trigger pulses.
- Booleans hold state, so set both the new value and clear the opposite where needed.
- Triggers fire once for transient feedback.
Centralizing this in one method keeps your input wiring consistent and easy to audit.
void applyMotion(MotionEvent event) {
switch (event) {
case MotionEvent.loading:
_isLoading?.value = true;
break;
case MotionEvent.idle:
_isLoading?.value = false;
break;
case MotionEvent.success:
_isLoading?.value = false;
_success?.fire();
break;
case MotionEvent.error:
_isLoading?.value = false;
_error?.fire();
break;
}
}Reading Input State Back via Listeners
Sometimes motion is driven by Rive itself (e.g. a draggable knob the user moves on the artboard) and you need the current value back in Dart. Inputs expose their value, and you can poll or react to it inside the state machine's change callback.
The StateMachineController also accepts an onStateChange callback so you can run Dart whenever the active state transitions, useful for analytics or chaining side effects.
void _onInit(Artboard artboard) {
final c = StateMachineController.fromArtboard(
artboard,
'KnobMachine',
onStateChange: (machineName, stateName) {
debugPrint('Entered $stateName in $machineName');
if (stateName == 'Snapped') {
HapticFeedback.lightImpact();
}
},
);
if (c != null) {
artboard.addController(c);
_angle = c.findSMI('angle') as SMINumber?;
}
}Lifecycle, Disposal, and Common Pitfalls
State machines are stateful resources. Treat them with the same discipline as controllers and subscriptions.
- Always dispose the
StateMachineControllerindispose()to release the artboard binding. - Null-check inputs:
findSMI/findInputreturn null if the name is misspelled or the artboard lacks that input — a silent no-op otherwise. - Match names exactly: input and state-machine names are case-sensitive and must match the
.rivfile. - Do not over-call setState: Rive repaints itself; rebuilding the whole subtree on every stream tick wastes frames.
Get these right and your input-driven motion stays smooth and leak-free.
Quick Check: Choosing the Right Input
You are wiring a Rive state machine to a form submit button. Tapping submit should play a one-time success checkmark animation that then returns to idle. Which input type and call is correct?
Recap: Reactive, Branching Motion
You now know how to make Rive animations follow your app instead of a fixed timeline.
- Three inputs: Boolean for held state, Number for continuous/blended values, Trigger for one-shot events.
- Wiring: build a
StateMachineControllerinonInit, attach it to the artboard, and cache input references. - Driving: assign to
valuefor booleans/numbers, callfire()for triggers, and feed continuous data from streams with clamping. - Architecture: model the branch decision in pure, testable Dart, then translate it to inputs in one central method.
- Hygiene: dispose the controller, cancel subscriptions, null-check inputs, and match names exactly.
With these patterns your animations become a live reflection of user input and model state.
Frequently asked questions
Is the “State Machines and Input-Driven Motion” lesson free?
Yes — the full text of “State Machines and Input-Driven Motion” is free to read here on the web, and the Flutter Mobile Development course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Flutter Mobile Development course, upgrade to CoddyKit PRO.
What will I learn in “State Machines and Input-Driven Motion”?
Wire Rive state machine inputs to app data for reactive, branching animations. You practise Flutter Mobile Development with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Flutter Mobile Development?
No prior experience is required. Flutter Mobile Development on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “State Machines and Input-Driven Motion” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Flutter Mobile Development lesson?
Yes. Every Flutter Mobile Development lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Embedding Rive Assets and Controllers
- State Machines and Input-Driven Motion
- Hero Transitions and Shared Element Motion
- Staggered and Choreographed AnimationControllers