基本食谱

此配方展示了一个基本示例，说明了如何使用 Navigation 3 API 实现两个屏幕。

工作原理

此示例定义了两个路由：RouteA 和 RouteB。RouteA 是表示简单屏幕的 data object，而 RouteB 是接受 id 作为参数的 data class。

mutableStateListOf<Any> 用于管理导航返回堆栈。

NavDisplay 可组合项用于显示当前界面。其 entryProvider 参数是一个 lambda，它接受来自返回堆栈的路线并返回 NavEntry。在 entryProvider 内，使用 when 语句根据路线确定要显示哪个可组合项。

如需从 RouteA 前往 RouteB，我们只需将 RouteB 实例添加到返回堆栈中。id 作为实参传递给 RouteB 数据类。

探索

在 GitHub 上查看完整配方。

/*
 * Copyright 2025 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.basic

import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.material3.Button
import androidx.compose.material3.Text
import androidx.compose.runtime.mutableStateListOf
import androidx.compose.runtime.remember
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

private data object RouteA

private data class RouteB(val id: String)

class BasicActivity : ComponentActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        setEdgeToEdgeConfig()
        super.onCreate(savedInstanceState)
        setContent {
            val backStack = remember { mutableStateListOf<Any>(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} ")
                        }

                        else -> {
                            error("Unknown route: $key")
                        }
                    }
                }
            )
        }
    }
}
BasicActivity.kt