Create Workflow

Create Workflow

Create properly structured Square Workflow classes following library conventions.

Quick Start

To create a new workflow, gather:

1. Workflow name (e.g., Login)
2. Stateful or Stateless — does it need internal state?
3. Props — input data from parent (Unit if none)
4. Output — events emitted to parent (Nothing if none)
5. Rendering — UI model returned each render pass (typically a Screen data class)

Step 1: Choose Workflow Type

StatefulWorkflow — use when you need internal state:

• Form data, loading states, error states
• Multi-step flows or navigation
• State that changes in response to events

StatelessWorkflow — use when rendering is a direct function of props:

• Simple pass-through or composition of child workflows
• No internal state needed
• Rendering derived entirely from props and child renderings

Step 2: Define Types

Props (input from parent)

data class MyWorkflowProps(val userId: String)
// Or use Unit if no props needed

State (StatefulWorkflow only)

State should use any Kotlin types - often a data class. If your state needs to be persisted to disk via a Snapshot it needs to be able to be converted to a ByteString.

// Simple state
data class MyState(val name: String, val isLoading: Boolean)

// Sealed state for distinct modes
sealed interface MyState {
  data object Loading : MyState
  data class Loaded(val data: String) : MyState
  data class Error(val message: String) : MyState
}

Output (events to parent)

// Multiple output types
sealed interface MyOutput {
  data object Completed : MyOutput
  data class Selected(val item: Item) : MyOutput
}

// Or use Nothing if no output is ever emitted

Rendering (view model)

Create in a separate file named [Feature]Screen.kt:

data class MyScreen(
  val title: String,
  val isLoading: Boolean,
  val onAction: () -> Unit,
  val onItemSelected: (Item) -> Unit
) : Screen

Step 3: Create Workflow Class

StatefulWorkflow — Object Pattern (no dependencies)

Use when the workflow has no injected dependencies:

object MyWorkflow : StatefulWorkflow<MyProps, MyState, MyOutput, MyScreen>() {

  override fun initialState(props: MyProps, snapshot: Snapshot?): MyState =
    MyState.Loading

  override fun render(
    renderProps: MyProps,
    renderState: MyState,
    context: RenderContext
  ): MyScreen {
    return MyScreen(
      title = renderProps.title,
      isLoading = renderState is MyState.Loading,
      {
        setOutput(MyOutput.Completed)
      },
      { item: Item ->
        state = MyState.Loaded(item.name)
      }
    )
  }

  override fun snapshotState(state: MyState): Snapshot? = null
}

StatefulWorkflow — Class Pattern (with dependencies)

Use when the workflow needs injected dependencies:

class MyWorkflow(
  private val repository: DataRepository,
) : StatefulWorkflow<MyProps, MyState, MyOutput, MyScreen>() {

  override fun initialState(props: MyProps, snapshot: Snapshot?): MyState =
    MyState.Loading

  override fun render(
    renderProps: MyProps,
    renderState: MyState,
    context: RenderContext
  ): MyScreen {
    // Run a worker for async data loading
    context.runningWorker(
      Worker.from { repository.fetchData(renderProps.id) },
      key = "fetchData-${renderProps.id}"
    ) { result ->
      action("dataLoaded") {
        state = MyState.Loaded(result)
      }
    }

    return MyScreen(
      title = renderProps.title,
      isLoading = renderState is MyState.Loading,
      {
        setOutput(MyOutput.Completed)
      }
    )
  }

  override fun snapshotState(state: MyState): Snapshot? = null
}

StatelessWorkflow

object MyWorkflow : StatelessWorkflow<MyProps, MyOutput, MyScreen>() {

  override fun render(
    renderProps: MyProps,
    context: RenderContext
  ): MyScreen {
    return MyScreen(
      title = renderProps.title,
      { action: String ->
        setOutput(MyOutput.ActionSelected(action))
      }
    )
  }
}

Factory Functions (inline definitions)

For simple workflows that don't need a named class:

// Stateful
val counterWorkflow = Workflow.stateful<Unit, Int, Nothing, Int>(
  initialState = 0,
  render = { state ->
    state
  }
)

// Stateless
val greetingWorkflow = Workflow.stateless<String, Nothing, String> { name ->
  "Hello, $name!"
}

Workers (Async Operations)

Use Workers for async work. Never perform side effects directly in render().

// Single-value worker from a suspend function
val worker = Worker.from { api.fetchUser(userId) }

// Multi-value worker from a Flow
val worker = repository.observeUpdates().asWorker()

// Custom worker with doesSameWorkAs for deduplication
class FetchWorker(private val id: String) : Worker<Data> {
  override fun run(): Flow<Data> = flow { emit(api.fetch(id)) }
  override fun doesSameWorkAs(otherWorker: Worker<*>): Boolean =
    otherWorker is FetchWorker && otherWorker.id == id
}

// Using a worker in render():
context.runningWorker(worker, key = "fetch") { result ->
  action("fetched") { state = MyState.Loaded(result) }
}

Child Workflows

// Render a child and handle its output
val childScreen = context.renderChild(
  child = ChildWorkflow,
  props = ChildProps(renderProps.itemId)
) { childOutput ->
  action("childOutput") {
    when (childOutput) {
      is ChildOutput.Done -> setOutput(MyOutput.Completed)
      is ChildOutput.Back -> state = MyState.Initial
    }
  }
}

// Child with Nothing output (no handler needed)
val childScreen = context.renderChild(ChildWorkflow, props = childProps)

Side Effects

For coroutine work that doesn't produce workflow output:

context.runningSideEffect("trackScreen") {
  analytics.trackScreenView("my_screen")
}

Critical Rules

1. Never perform side effects in render() — render is called multiple times per state. Use runningWorker or runningSideEffect.
2. Don't capture renderState in lambdas — renderState is a snapshot from render time and will be stale when the action fires. This includes local variables derived from renderState (easy to miss!). Always read from state on the Updater receiver inside action/eventHandler lambdas. For sealed state hierarchies, use safeAction<SpecificState>("name") which no-ops if the state type has changed. See AGENTS.md "Common Pitfalls" for detailed examples.
3. Always provide name to eventHandler — Required for Compose stability and debugging.
4. Use setOutput() to emit output — Call at most once per action.
5. Return null from snapshotState unless you need state persistence across process death.

Naming Conventions

File Organization

feature/
├── MyWorkflow.kt          # Workflow + Props + State + Output
└── MyScreen.kt            # Rendering class (separate file)

Required Imports

// Core workflow types
import com.squareup.workflow1.StatefulWorkflow  // or StatelessWorkflow
import com.squareup.workflow1.Snapshot
import com.squareup.workflow1.action

// Workers
import com.squareup.workflow1.Worker
import com.squareup.workflow1.runningWorker
import com.squareup.workflow1.asWorker

// UI rendering
import com.squareup.workflow1.ui.Screen

// Factory functions
import com.squareup.workflow1.Workflow
import com.squareup.workflow1.stateful
import com.squareup.workflow1.stateless

Documentation

• Main docs: https://square.github.io/workflow/
• Kotlin API: https://square.github.io/workflow/kotlin/api/htmlMultiModule/
• Tutorial: https://github.com/square/workflow-kotlin/tree/main/samples/tutorial

Output

When creating a workflow, always:

1. Determine whether StatefulWorkflow or StatelessWorkflow is needed
2. Define Props, State (if stateful), Output, and Rendering types
3. Create the workflow class with proper type parameters
4. Create the Screen rendering in a separate file
5. Use eventHandler("name") for UI events
6. Use Workers for async operations
7. Ensure all imports are correct