LocalLifecycleOwner 配方

此配方演示了如何在 Navigation 3 条目中使用 LifecycleResumeEffect，以根据条目的生命周期状态暂停和恢复工作。

运作方式

在 Navigation 3 中，默认情况下，每个 NavEntry 都会通过 LocalLifecycleOwner.current 获得自己的 LifecycleOwner。这意味着，条目内的任何生命周期感知型组件都会自动限定为 NavEntry 的范围。

使用对话框场景的 LifecycleResumeEffect

  1. RouteA（屏幕）：

    • 使用限定为 NavEntry 的 LocalLifecycleOwner.current 的 LifecycleResumeEffect(Unit)，以便在 RESUMED 状态下推进 LinearProgressIndicator。
    • 每当 progressValue 达到 1f 时，都会自动将其重置为 0f。

  2. RouteB（对话框）：

    • 使用 DialogSceneStrategy.dialog() 配置为对话框。
    • 当用户打开 RouteB 对话框时，RouteA 会在 STARTED 状态下（离开 RESUMED）在对话框后面保持可见。
    • LifecycleResumeEffect 会调用 onPauseOrDispose，暂停进度指示器。
    • 当对话框被关闭时，RouteA 会返回到 RESUMED，并且 LifecycleResumeEffect 会自动恢复进度指示器。
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package com.example.nav3recipes.lifecycleowner

import android.os.Bundle
import android.util.Log
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.animation.core.LinearEasing
import androidx.compose.animation.core.animateFloatAsState
import androidx.compose.animation.core.snap
import androidx.compose.animation.core.tween
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.Spacer
import androidx.compose.foundation.layout.height
import androidx.compose.foundation.layout.padding
import androidx.compose.material3.AlertDialog
import androidx.compose.material3.Button
import androidx.compose.material3.LinearProgressIndicator
import androidx.compose.material3.Text
import androidx.compose.runtime.Composable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableFloatStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.rememberCoroutineScope
import androidx.compose.runtime.setValue
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.unit.dp
import androidx.lifecycle.Lifecycle
import androidx.lifecycle.compose.LifecycleEventEffect
import androidx.lifecycle.compose.LifecycleResumeEffect
import androidx.lifecycle.compose.dropUnlessResumed
import androidx.navigation3.runtime.NavKey
import androidx.navigation3.runtime.entryProvider
import androidx.navigation3.runtime.rememberNavBackStack
import androidx.navigation3.scene.DialogSceneStrategy
import androidx.navigation3.ui.NavDisplay
import com.example.nav3recipes.content.ContentGreen
import com.example.nav3recipes.ui.setEdgeToEdgeConfig
import kotlinx.coroutines.delay
import kotlinx.coroutines.launch
import kotlinx.serialization.Serializable
import kotlin.time.Duration.Companion.milliseconds

@Serializable
private data object RouteA : NavKey

@Serializable
private data object RouteB : NavKey

class LifecycleOwnerActivity : ComponentActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        setEdgeToEdgeConfig()
        super.onCreate(savedInstanceState)
        setContent {
            val backStack = rememberNavBackStack(RouteA)
            val dialogStrategy = remember { DialogSceneStrategy<NavKey>() }

            NavDisplay(
                backStack = backStack,
                onBack = backStack::removeLastOrNull,
                sceneStrategies = listOf(dialogStrategy),
                entryProvider = entryProvider {
                    entry<RouteA> {
                        LogLifecycleEffect("ScreenA")
                        ContentGreen("Screen A") {
                            var progressValue by remember { mutableFloatStateOf(0f) }
                            val coroutineScope = rememberCoroutineScope()

                            val animatedProgress by animateFloatAsState(
                                targetValue = progressValue,
                                animationSpec = if (progressValue == 0f) snap() else tween(durationMillis = 100, easing = LinearEasing),
                                label = "ProgressAnimation"
                            )

                            // LifecycleResumeEffect runs only while ScreenA is in the RESUMED state.
                            // When the dialog opens, ScreenA transitions to PAUSED, which calls onPauseOrDispose.
                            LifecycleResumeEffect(Unit) {
                                val job = coroutineScope.launch {
                                    while (true) {
                                        delay(100.milliseconds)
                                        progressValue += 0.01f
                                        if (progressValue >= 1f) {
                                            progressValue = 0f
                                        }
                                    }
                                }
                                onPauseOrDispose {
                                    job.cancel()
                                }
                            }

                            Column(
                                horizontalAlignment = Alignment.CenterHorizontally,
                                modifier = Modifier.padding(16.dp)
                            ) {
                                LinearProgressIndicator(progress = { animatedProgress })
                                Spacer(modifier = Modifier.height(16.dp))
                                Button(onClick = dropUnlessResumed { backStack.add(RouteB) }) {
                                    Text("Open Dialog")
                                }
                            }
                        }
                    }
                    entry<RouteB>(metadata = DialogSceneStrategy.dialog()) {
                        LogLifecycleEffect("Dialog")
                        AlertDialog(
                            onDismissRequest = backStack::removeLastOrNull,
                            title = { Text("Dialog") },
                            text = {
                                Text("Screen A is no longer in resumed state, pausing the progress indicator.")
                            },
                            confirmButton = {
                                Button(onClick = dropUnlessResumed { backStack.removeLastOrNull() }) {
                                    Text("Dismiss Dialog")
                                }
                            }
                        )
                    }
                }
            )
        }
    }
}

@Composable
private fun LogLifecycleEffect(screenName: String) {
    LifecycleEventEffect(Lifecycle.Event.ON_CREATE) {
        Log.d("LifecycleOwner", "$screenName: ON_CREATE")
    }
    LifecycleEventEffect(Lifecycle.Event.ON_START) {
        Log.d("LifecycleOwner", "$screenName: ON_START")
    }
    LifecycleEventEffect(Lifecycle.Event.ON_RESUME) {
        Log.d("LifecycleOwner", "$screenName: ON_RESUME")
    }
    LifecycleEventEffect(Lifecycle.Event.ON_PAUSE) {
        Log.d("LifecycleOwner", "$screenName: ON_PAUSE")
    }
    LifecycleEventEffect(Lifecycle.Event.ON_STOP) {
        Log.d("LifecycleOwner", "$screenName: ON_STOP")
    }
    // Note that ON_DESTROY event is not observable from composables.
}