使用Navigation时出现主线程帧丢失问题求助

错误日志 #

I/Choreographer: Skipped 204 frames!  The application may be doing too much work on its main thread.

场景描述 #

基于Firebase Storage存储、Media3播放的音乐流应用，单页面实现歌曲列表+播放控制时运行正常；使用Navigation拆分为两个页面（点击歌曲跳转至播放控制页）后，出现上述主线程丢帧错误。

相关代码 #

网络请求代码 #

TrackRepository.kt

class TrackRepository {

    private val storage = Firebase.storage
    private val trackRef = storage.reference

    suspend fun getTracks() = suspendCoroutine<List<Track>> { result ->
        val trackList = mutableListOf<Track>()
            try {
                Firebase.firestore.collection(Constants.TRACK).get().addOnCompleteListener { task ->
                    var index = 0
                    task.result.forEach { document ->
                        val trackUrl = trackRef.child(document.getString(Constants.FILENAME)!!)

                        trackUrl.downloadUrl.addOnSuccessListener { trackDownloadUrl ->
                            trackList.add(
                                document.toTrack(
                                    trackDownloadUrl.toString()
                                )
                            )
                            if (index == task.result.size() - 1) {
                                result.resume(trackList)
                            }
                            index++
                        }

                    }
                }

            } catch (e: Exception) {
                e.printStackTrace()
            }

    }

}

TrackViewModel.kt

@HiltViewModel
class TrackViewModel @Inject constructor(trackRepository: TrackRepository): ViewModel() {
    private val _trackList = MutableLiveData<List<Track>>()
    val trackList : LiveData<List<Track>> get() = _trackList

    init {
        viewModelScope.launch() {
            trackRepository.getTracks().let {
                _trackList.postValue(it.sortedBy { it.fileName })
            }
        }
    }
}

导航相关代码 #

NavHost中PlayerScreen配置

composable("player_screen"){
    val result = navController.previousBackStackEntry?.savedStateHandle?.get<MyTrack>("track")
   PlayerScreen(
     navController = navController,
       onMusicPlayerClick = onMusicPlayerClick,
       track = result?.track!!,
       onTrackItemClick = onTrackItemClick,
       trackList = trackList,
       isPlaying = isPlaying,

   )

}

歌曲列表页跳转代码

if (selected){

        val newTrack = MyTrack(track, navController, onMusicPlayerClick)
        navController.currentBackStackEntry?.savedStateHandle?.set(
            key = "track",
            value = newTrack
        )
    onTrackItemClick(track)
    navController.navigate("player_screen")


}

已排查情况 #

• 排除网络请求原因：单页面模式下无丢帧问题；
• 移除离线下载功能后问题依旧；
• 用LaunchedEffect(Unit)包裹导航代码可解决，但引发其他逻辑问题；
• Android Profiler未定位到明确的耗时操作。

定位分析与解决方案 #

核心问题定位 #

1. TrackRepository异步逻辑漏洞：当前getTracks中，downloadUrl是异步请求，回调执行顺序不固定，index++写在回调外部，导致result.resume(trackList)可能在所有下载URL请求完成前就被调用，后续回调仍在主线程修改列表，引发主线程额外负载；同时trackList是 mutable 集合，多线程回调修改存在线程安全问题。
2. 导航数据传递不合理：跳转时传递的MyTrack包含navController和回调对象，这类对象不适合通过savedStateHandle传递，序列化/反序列化过程可能在主线程产生耗时，且容易引发内存泄漏。
3. 列表排序主线程开销：sortedBy在ViewModel的viewModelScope（默认主线程）执行，若歌曲列表数量大，排序操作会占用主线程时间片。

具体修复方案 #

1. 修复TrackRepository的异步逻辑

改用coroutineScope并行处理所有下载URL请求，确保所有请求完成后再返回列表，同时避免线程安全问题：

class TrackRepository {

    private val storage = Firebase.storage
    private val trackRef = storage.reference
    private val firestore = Firebase.firestore

    suspend fun getTracks(): List<Track> = coroutineScope {
        try {
            val trackDocs = firestore.collection(Constants.TRACK).get().await()
            trackDocs.map { document ->
                async {
                    val fileName = document.getString(Constants.FILENAME)!!
                    val trackDownloadUrl = trackRef.child(fileName).downloadUrl.await()
                    document.toTrack(trackDownloadUrl.toString())
                }
            }.awaitAll().sortedBy { it.fileName }
        } catch (e: Exception) {
            e.printStackTrace()
            emptyList()
        }
    }
}

说明：使用Firebase Kotlin扩展库的await()方法替代回调，async/awaitAll并行处理所有下载URL请求，效率更高且逻辑安全。

2. 优化导航数据传递

不要传递包含navController和回调的MyTrack，仅传递Track实体：

• 列表页跳转代码修改：

if (selected) {
    navController.currentBackStackEntry?.savedStateHandle?.set(
        key = "track",
        value = track // 仅传递Track实体
    )
    onTrackItemClick(track)
    navController.navigate("player_screen")
}

• PlayerScreen获取数据：

composable("player_screen"){
    val track = navController.previousBackStackEntry?.savedStateHandle?.get<Track>("track")!!
    // 通过LocalNavHostController获取导航控制器，无需传递
    val localNavController = LocalNavHostController.current
    PlayerScreen(
        navController = localNavController,
        onMusicPlayerClick = onMusicPlayerClick,
        track = track,
        onTrackItemClick = onTrackItemClick,
        trackList = trackList,
        isPlaying = isPlaying,
    )
}

3. 移除非UI线程的排序操作

在Repository中完成排序，避免主线程开销：

// 在TrackRepository的getTracks方法最后添加排序
return trackDocs.map { ... }.awaitAll().sortedBy { it.fileName }

ViewModel中直接赋值即可：

viewModelScope.launch {
    _trackList.postValue(trackRepository.getTracks())
}

4. 排查PlayerScreen的初始化耗时

检查PlayerScreen中是否在组合阶段直接执行Media3播放器初始化、大量UI计算等操作，这类操作应放到LaunchedEffect或ViewModel的viewModelScope中执行：

@Composable
fun PlayerScreen(...) {
    LaunchedEffect(track) {
        // 初始化播放器、加载媒体资源等耗时操作
        player.prepare()
    }
}

内容的提问来源于stack exchange，提问作者Dilshad