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split up into multiple files, wrote design for better state management
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10 files changed

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‎samples/containers/thingy/src/main/java/com/squareup/sample/thingy/BackStackFactory.kt‎

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package com.squareup.sample.thingy
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import com.squareup.workflow1.ui.Screen
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import com.squareup.workflow1.ui.navigation.BackStackScreen
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import com.squareup.workflow1.ui.navigation.toBackStackScreen
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import kotlin.coroutines.AbstractCoroutineContextElement
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import kotlin.coroutines.CoroutineContext
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public fun interface BackStackFactory {
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/**
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* Responsible for converting a list of [Screen]s into a [BackStackScreen]. This function *must*
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* handle the case where [screens] is empty, since [BackStackScreen] must always have at least
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* one screen. It *should* handle the case where [isTopIdle] is true, which indicates that the
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* top (last) screen in [screens] is doing some work that may eventually show another screen.
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*
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* @see toBackStackScreen
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*/
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fun createBackStack(
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screens: List<Screen>,
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isTopIdle: Boolean
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): BackStackScreen<Screen>
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companion object {
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internal val ThrowOnIdle
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get() = showLoadingScreen {
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error("No BackStackFactory provided")
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}
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/**
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* Returns a [BackStackFactory] that shows a [loading screen][createLoadingScreen] when
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* [BackStackWorkflow.runBackStack] has not shown anything yet or when a workflow's output
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* handler is idle (not showing an active screen).
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*/
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fun showLoadingScreen(
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name: String = "",
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createLoadingScreen: () -> Screen
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): BackStackFactory = BackStackFactory { screens, isTopIdle ->
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val mutableScreens = screens.toMutableList()
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if (mutableScreens.isEmpty() || isTopIdle) {
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mutableScreens += createLoadingScreen()
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}
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mutableScreens.toBackStackScreen(name)
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}
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}
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}
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/**
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* Returns a [CoroutineContext.Element] that will store this [BackStackFactory] in a
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* [CoroutineContext] to later be retrieved by [backStackFactory].
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*/
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public fun BackStackFactory.asContextElement(): CoroutineContext.Element =
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BackStackFactoryContextElement(this)
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/**
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* Looks for a [BackStackFactory] stored the current context via [asContextElement].
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*/
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public val CoroutineContext.backStackFactory: BackStackFactory?
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get() = this[BackStackFactoryContextElement]?.factory
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private class BackStackFactoryContextElement(
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val factory: BackStackFactory
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) : AbstractCoroutineContextElement(Key) {
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companion object Key : CoroutineContext.Key<BackStackFactoryContextElement>
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}

‎samples/containers/thingy/src/main/java/com/squareup/sample/thingy/BackStackFrame.kt‎

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package com.squareup.sample.thingy
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import com.squareup.workflow1.Sink
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import com.squareup.workflow1.StatefulWorkflow.RenderContext
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import com.squareup.workflow1.Workflow
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import com.squareup.workflow1.WorkflowAction
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import com.squareup.workflow1.WorkflowAction.Companion
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import com.squareup.workflow1.ui.Screen
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import kotlinx.coroutines.CompletableDeferred
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import kotlinx.coroutines.CoroutineScope
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import kotlinx.coroutines.CoroutineStart.UNDISPATCHED
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import kotlinx.coroutines.Job
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import kotlinx.coroutines.cancel
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import kotlinx.coroutines.currentCoroutineContext
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import kotlinx.coroutines.ensureActive
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import kotlinx.coroutines.job
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import kotlinx.coroutines.launch
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internal sealed interface BackStackFrame<R> {
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fun cancelCaller()
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suspend fun awaitResult(): R
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suspend fun cancelSelf(): Nothing
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fun cancel()
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}
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/**
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* Represents a call to [BackStackScope.showWorkflow].
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*/
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internal class WorkflowFrame<PropsT, OutputT, ChildPropsT, ChildOutputT, R> private constructor(
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private val workflow: Workflow<ChildPropsT, ChildOutputT, Screen>,
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private val props: ChildPropsT,
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private val callerJob: Job,
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private val frameScope: CoroutineScope,
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private val onOutput: suspend BackStackWorkflowScope.(ChildOutputT) -> R,
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private val actionSink: Sink<WorkflowAction<PropsT, BackStackState, OutputT>>,
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private val parent: BackStackFrame<*>?,
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private val result: CompletableDeferred<R>,
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) : BackStackFrame<R> {
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constructor(
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workflow: Workflow<ChildPropsT, ChildOutputT, Screen>,
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initialProps: ChildPropsT,
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callerJob: Job,
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frameScope: CoroutineScope,
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onOutput: suspend BackStackWorkflowScope.(ChildOutputT) -> R,
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actionSink: Sink<WorkflowAction<PropsT, BackStackState, OutputT>>,
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parent: BackStackFrame<*>?,
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) : this(
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workflow = workflow,
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props = initialProps,
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callerJob = callerJob,
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frameScope = frameScope,
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onOutput = onOutput,
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actionSink = actionSink,
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parent = parent,
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result = CompletableDeferred(parent = frameScope.coroutineContext.job)
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)
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fun copy(
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props: ChildPropsT = this.props,
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): WorkflowFrame<PropsT, OutputT, ChildPropsT, ChildOutputT, R> = WorkflowFrame(
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workflow = workflow,
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props = props,
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callerJob = callerJob,
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frameScope = frameScope,
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onOutput = onOutput,
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actionSink = actionSink,
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parent = parent,
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result = result
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)
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override suspend fun awaitResult(): R = result.await()
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override fun cancelCaller() {
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callerJob.cancel()
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}
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private suspend fun finishWith(value: R): Nothing {
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result.complete(value)
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cancelSelf()
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}
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override suspend fun cancelSelf(): Nothing {
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cancel()
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val currentContext = currentCoroutineContext()
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currentContext.cancel()
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currentContext.ensureActive()
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error("Nonsense")
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}
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override fun cancel() {
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frameScope.cancel()
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}
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fun renderWorkflow(
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context: RenderContext<PropsT, BackStackState, OutputT>
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): Screen = context.renderChild(
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child = workflow,
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props = props,
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handler = ::onOutput
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)
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private fun onOutput(output: ChildOutputT): WorkflowAction<PropsT, BackStackState, OutputT> {
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var canAcceptAction = true
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var action: WorkflowAction<PropsT, BackStackState, OutputT>? = null
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val sink = object : Sink<WorkflowAction<PropsT, BackStackState, OutputT>> {
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override fun send(value: WorkflowAction<PropsT, BackStackState, OutputT>) {
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val sendToSink = synchronized(result) {
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if (canAcceptAction) {
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action = value
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canAcceptAction = false
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false
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} else {
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true
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}
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}
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if (sendToSink) {
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actionSink.send(value)
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}
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}
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}
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// Run synchronously until first suspension point since in many cases it will immediately
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// either call showWorkflow, finishWith, or goBack, and so then we can just return that action
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// immediately instead of needing a whole separate render pass.
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frameScope.launch(start = UNDISPATCHED) {
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val showScope = BackStackWorkflowScopeImpl(
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actionSink = sink,
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coroutineScope = this,
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thisFrame = this@WorkflowFrame,
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parentFrame = parent
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)
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finishWith(onOutput(showScope, output))
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}
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// TODO collect WorkflowAction
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// Once the coroutine has suspended, all sends must go to the real sink.
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return synchronized(result) {
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canAcceptAction = false
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action ?: WorkflowAction.noAction()
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}
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}
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}
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/**
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* Represents a call to [BackStackScope.showScreen].
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*/
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internal class ScreenFrame<OutputT, R>(
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private val callerJob: Job,
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private val frameScope: CoroutineScope,
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private val actionSink: Sink<WorkflowAction<Any?, BackStackState, OutputT>>,
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private val parent: BackStackFrame<*>?,
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) : BackStackFrame<R> {
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private val result = CompletableDeferred<R>()
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lateinit var screen: Screen
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private set
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fun initScreen(screenFactory: BackStackScreenScope<R>.() -> Screen) {
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val factoryScope = BackStackScreenScopeImpl<Any?, OutputT, R>(
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actionSink = actionSink,
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coroutineScope = frameScope,
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thisFrame = this,
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parentFrame = parent
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)
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screen = screenFactory(factoryScope)
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}
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override suspend fun awaitResult(): R = result.await()
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override fun cancelCaller() {
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callerJob.cancel()
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}
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fun continueWith(value: R) {
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result.complete(value)
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cancel()
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}
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override suspend fun cancelSelf(): Nothing {
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cancel()
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val currentContext = currentCoroutineContext()
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currentContext.cancel()
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currentContext.ensureActive()
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error("Nonsense")
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}
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override fun cancel() {
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frameScope.cancel()
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}
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}

‎samples/containers/thingy/src/main/java/com/squareup/sample/thingy/BackStackScopeImpl.kt‎

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package com.squareup.sample.thingy
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import com.squareup.workflow1.Sink
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import com.squareup.workflow1.Workflow
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import com.squareup.workflow1.WorkflowAction
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import com.squareup.workflow1.ui.Screen
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import kotlinx.coroutines.CoroutineScope
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import kotlinx.coroutines.flow.Flow
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internal class BackStackScopeImpl<OutputT>(
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coroutineScope: CoroutineScope,
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) : BackStackScope, CoroutineScope by coroutineScope {
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// TODO set this
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lateinit var actionSink: Sink<WorkflowAction<Any?, BackStackState, OutputT>>
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override suspend fun <ChildPropsT, ChildOutputT, R> showWorkflow(
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workflow: Workflow<ChildPropsT, ChildOutputT, Screen>,
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props: Flow<ChildPropsT>,
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onOutput: suspend BackStackWorkflowScope.(ChildOutputT) -> R
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): R = showWorkflowImpl(
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workflow = workflow,
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props = props,
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onOutput = onOutput,
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actionSink = actionSink,
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parentFrame = null
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)
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override suspend fun <R> showScreen(
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screenFactory: BackStackScreenScope<R>.() -> Screen
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): R = showScreenImpl(
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screenFactory = screenFactory,
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actionSink = actionSink,
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parentFrame = null
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)
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}

‎samples/containers/thingy/src/main/java/com/squareup/sample/thingy/BackStackScreenScopeImpl.kt‎

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package com.squareup.sample.thingy
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import com.squareup.workflow1.Sink
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import com.squareup.workflow1.Workflow
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import com.squareup.workflow1.WorkflowAction
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import com.squareup.workflow1.action
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import com.squareup.workflow1.ui.Screen
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import kotlinx.coroutines.CoroutineScope
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import kotlinx.coroutines.flow.Flow
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internal class BackStackScreenScopeImpl<PropsT, OutputT, R>(
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private val actionSink: Sink<WorkflowAction<PropsT, BackStackState, OutputT>>,
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coroutineScope: CoroutineScope,
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private val thisFrame: ScreenFrame<OutputT, R>,
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private val parentFrame: BackStackFrame<*>?,
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) : BackStackScreenScope<R>, CoroutineScope by coroutineScope {
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override suspend fun <ChildPropsT, ChildOutputT, R> showWorkflow(
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workflow: Workflow<ChildPropsT, ChildOutputT, Screen>,
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props: Flow<ChildPropsT>,
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onOutput: suspend BackStackWorkflowScope.(ChildOutputT) -> R
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): R = showWorkflowImpl(
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workflow = workflow,
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props = props,
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onOutput = onOutput,
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actionSink = actionSink,
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parentFrame = thisFrame,
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)
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@Suppress("UNCHECKED_CAST")
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override suspend fun <R> showScreen(
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screenFactory: BackStackScreenScope<R>.() -> Screen
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): R = showScreenImpl(
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screenFactory = screenFactory,
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actionSink = actionSink as Sink<WorkflowAction<Any?, BackStackState, OutputT>>,
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parentFrame = thisFrame,
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)
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override fun continueWith(value: R) {
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thisFrame.continueWith(value)
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}
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override fun cancelScreen() {
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// If parent is null, goBack will not be exposed and will never be called.
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val parent = checkNotNull(parentFrame) { "goBack called on root scope" }
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actionSink.send(action("popTo") {
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state = state.popToFrame(parent)
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})
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thisFrame.cancel()
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}
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}

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