基本 Parcelable 食谱

此食谱展示了一个基本示例，说明如何在不使用 kotlinx.serialization 的情况下创建在配置更改后仍保留的返回堆栈。它使用 Android 的 Parcelable 和 kotlin-parcelize 插件来保存和恢复导航状态。

工作原理

在此示例中，RouteA 和 RouteB 实现了一个标记接口 Route，该接口本身扩展了 Parcelable。它们还使用 kotlin-parcelize 插件中的 @Parcelize 进行注解，该插件会自动生成 Parcelable 实现：

sealed interface Route : Parcelable

@Parcelize
data object RouteA : Route

@Parcelize
data class RouteB(val id: String) : Route

为了使返回堆栈保持不变，此食谱定义了 rememberParcelableBackStack 函数。为了确保 NavDisplay 和其他可组合项知道返回堆栈的更改，返回堆栈存储在 SnapshotStateList 中。

@Composable
fun <T : Parcelable> rememberParcelableBackStack(vararg elements: T): SnapshotStateList<T> {
    return rememberSaveable {
        mutableStateListOf(*elements)
    }
}

这可以替代 androidx.navigation3.runtime 中的内置 rememberNavBackStack，后者依赖于 kotlinx.serialization。如果您的应用严格偏好 Parcelable 并且避免依赖于 kotlinx.serialization，请使用此方法。

/*
 * Copyright 2026 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.nav3recipes.basicparcelable

import android.os.Bundle
import android.os.Parcelable
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.material3.Button
import androidx.compose.material3.Text
import androidx.compose.runtime.Composable
import androidx.compose.runtime.mutableStateListOf
import androidx.compose.runtime.saveable.rememberSaveable
import androidx.compose.runtime.snapshots.SnapshotStateList
import androidx.lifecycle.compose.dropUnlessResumed
import androidx.navigation3.runtime.NavEntry
import androidx.navigation3.ui.NavDisplay
import com.example.nav3recipes.content.ContentBlue
import com.example.nav3recipes.content.ContentGreen
import com.example.nav3recipes.ui.setEdgeToEdgeConfig
import kotlinx.parcelize.Parcelize

sealed interface Route : Parcelable

@Parcelize
data object RouteA : Route

@Parcelize
data class RouteB(val id: String) : Route

/**
 * Creates and remembers a [SnapshotStateList] to hold a back stack of [Parcelable] routes
 * that survives configuration changes and process death.
 *
 * @param T The route type, which must implement [Parcelable].
 * @param elements The initial routes to populate the back stack.
 * @return A reactive [SnapshotStateList] managing the navigation back stack.
 */
@Composable
fun <T : Parcelable> rememberParcelableBackStack(vararg elements: T): SnapshotStateList<T> {
    return rememberSaveable {
        mutableStateListOf(*elements)
    }
}

class BasicParcelableActivity : ComponentActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        setEdgeToEdgeConfig()
        super.onCreate(savedInstanceState)
        setContent {
            val backStack = rememberParcelableBackStack<Route>(RouteA)

            NavDisplay(
                backStack = backStack,
                onBack = { backStack.removeLastOrNull() },
                entryProvider = { key ->
                    when (key) {
                        is RouteA -> NavEntry(key) {
                            ContentGreen("Welcome to Nav3") {
                                Button(onClick = dropUnlessResumed {
                                    backStack.add(RouteB("123"))
                                }) {
                                    Text("Click to navigate")
                                }
                            }
                        }

                        is RouteB -> NavEntry(key) {
                            ContentBlue("Route id: ${key.id} ")
                        }
                    }
                }
            )
        }
    }
}