条件付きトランジションのレシピ
このレシピでは、transitionSpec と popTransitionSpec を使用して Navigation 3 でルート依存の画面遷移を作成する方法を示します。スライドの方向（右、左、下、上）は、initialState と targetState のナビゲーション キーのペアに基づいて条件付きで選択されます。
仕組み
- ルート定義: ナビゲーションの宛先（
Step1、Step2、Step3、Step4）は、NavKeyを実装し、@Serializableでマークされた sealed クラス階層を使用して定義されます。 - 条件付きの転送トランジション（
transitionSpec）:(initialKey to targetKey)のペアを照合して、スライド アニメーションの方向を決定します。Step1$\rightarrow$Step2: 左にスワイプStep2$\rightarrow$Step3: 上にスワイプStep3$\rightarrow$Step4: 右にスワイプStep4$\rightarrow$Step1: 下にスライド（フローを再開）
- 条件付きポップ トランジション（
popTransitionSpec）: 戻るナビゲーション時やバックスタックのクリア時に、スライドの逆方向を処理します。 - Backstack Control: シームレスなトップスライド トランジションを実行しながら、最終ステップ（
backStack.clear()とbackStack.add(Step1)）でナビゲーション スタックをクリアする方法を示します。
package com.example.nav3recipes.conditionaltransitions import android.os.Bundle import androidx.activity.ComponentActivity import androidx.activity.compose.setContent import androidx.compose.animation.ContentTransform import androidx.compose.animation.slideInHorizontally import androidx.compose.animation.slideInVertically import androidx.compose.animation.slideOutHorizontally import androidx.compose.animation.slideOutVertically import androidx.compose.animation.togetherWith import androidx.compose.foundation.layout.Arrangement import androidx.compose.foundation.layout.Column import androidx.compose.foundation.layout.Row import androidx.compose.foundation.layout.fillMaxSize import androidx.compose.foundation.layout.fillMaxWidth import androidx.compose.foundation.layout.padding import androidx.compose.material3.ElevatedButton import androidx.compose.material3.Scaffold import androidx.compose.material3.Text import androidx.compose.runtime.Composable import androidx.compose.ui.Alignment import androidx.compose.ui.Modifier import androidx.navigation3.runtime.NavKey import androidx.navigation3.runtime.entryProvider import androidx.navigation3.runtime.rememberNavBackStack import androidx.navigation3.ui.NavDisplay import com.example.nav3recipes.content.ContentGreen import com.example.nav3recipes.content.ContentOrange import com.example.nav3recipes.content.ContentPurple import com.example.nav3recipes.content.ContentRed import com.example.nav3recipes.sharedviewmodel.toContentKey import com.example.nav3recipes.ui.setEdgeToEdgeConfig import dagger.hilt.android.AndroidEntryPoint import kotlinx.serialization.Serializable @Serializable sealed class Step(val firstButtonTitle: String, val secondButtonTitle: String) : NavKey @Serializable data object Step1 : Step("Home", "Swipe left") @Serializable data object Step2 : Step("Swipe right", "Swipe up") @Serializable data object Step3 : Step("Swipe down", "Swipe right") @Serializable data object Step4 : Step("Swipe left", "Swipe down") @AndroidEntryPoint class ConditionalTransitionsActivity : ComponentActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setEdgeToEdgeConfig() setContent { Scaffold { paddingValues -> val backStack = rememberNavBackStack(Step1) NavDisplay( backStack = backStack, modifier = Modifier.padding(paddingValues), onBack = backStack::removeLastOrNull, entryProvider = entryProvider { entry<Step1> { ContentGreen(title = "Screen 1") { StepContent( step = it, onNext = { backStack += Step2 }, onBack = ::finish, // closing the activity ) } } entry<Step2> { ContentRed(title = "Screen 2") { StepContent( step = it, onNext = { backStack += Step3 }, onBack = backStack::removeLastOrNull, ) } } entry<Step3> { ContentOrange(title = "Screen 3") { StepContent( step = it, onNext = { backStack += Step4 }, onBack = backStack::removeLastOrNull, ) } } entry<Step4> { ContentPurple(title = "Screen 4") { StepContent( step = it, onNext = { backStack.clear() backStack.add(Step1) }, onBack = backStack::removeLastOrNull, ) } } }, transitionSpec = { val initialKey = initialState.entries.lastOrNull()?.contentKey val targetKey = targetState.entries.lastOrNull()?.contentKey when (initialKey to targetKey) { Step1.toContentKey() to Step2.toContentKey() -> swipeLeft() Step2.toContentKey() to Step3.toContentKey() -> swipeUp() Step3.toContentKey() to Step4.toContentKey() -> swipeRight() Step4.toContentKey() to Step1.toContentKey() -> swipeDown() else -> swipeRight() } }, popTransitionSpec = { val initialKey = initialState.entries.lastOrNull()?.contentKey val targetKey = targetState.entries.lastOrNull()?.contentKey when (initialKey to targetKey) { Step4.toContentKey() to Step1.toContentKey() -> swipeDown() // via backstack clearing Step2.toContentKey() to Step1.toContentKey() -> swipeRight() Step3.toContentKey() to Step2.toContentKey() -> swipeDown() Step4.toContentKey() to Step3.toContentKey() -> swipeLeft() else -> swipeLeft() } }, ) } } } } @Composable fun StepContent(step: Step, onNext: () -> Unit, onBack: () -> Unit) { Column( verticalArrangement = Arrangement.SpaceEvenly, horizontalAlignment = Alignment.CenterHorizontally, modifier = Modifier.fillMaxSize() ) { Row(horizontalArrangement = Arrangement.SpaceEvenly, modifier = Modifier.fillMaxWidth()) { ElevatedButton(onBack) { Text(text = step.firstButtonTitle) } ElevatedButton(onNext) { Text(text = step.secondButtonTitle) } } } } private fun swipeLeft(): ContentTransform = slideInHorizontally(initialOffsetX = { it }) togetherWith slideOutHorizontally(targetOffsetX = { -it }) private fun swipeUp(): ContentTransform = slideInVertically(initialOffsetY = { it }) togetherWith slideOutVertically(targetOffsetY = { -it }) private fun swipeRight(): ContentTransform = slideInHorizontally(initialOffsetX = { -it }) togetherWith slideOutHorizontally(targetOffsetX = { it }) private fun swipeDown(): ContentTransform = slideInVertically(initialOffsetY = { -it }) togetherWith slideOutVertically(targetOffsetY = { it })