android - 在Fragment中处理Coroutine的正确方法

Question

以下挂起函数会在 1 秒延迟内更新进度条和 2 个 TextView。进度条指示 MP3 的进度，TextView 分别指示已用时间和剩余时间。

用户可以离开 fragment 并再次返回，这意味着 fragment ( View )被销毁并再次创建。

我想知道这个实现是否正确和/或是否有更好的实现和/或替代方案(第一次实现协程)。这是一些代码:

class BookViewFragment : Fragment(), CoroutineScope {
    private var _binding: FragmentBookViewerBinding? = null
    private val bookViewFragmentBinding get() = _binding!!

    private lateinit var job: Job
    override val coroutineContext: CoroutineContext
        get() = Dispatchers.Main + job

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        _binding = FragmentBookViewerBinding.inflate(layoutInflater)
        val view = bookViewFragmentBinding.root
        job = Job()
        initMediaPlayer()
        return view
    }

    override fun onDestroyView() {
        super.onDestroyView()
        job.cancel()
        _binding = null
        mp.stop()
        mp.release()
    }

    private fun initMediaPlayer() {
        mp = MediaPlayer()

        mp.run {
            setDataSource(...)
            setVolume(0.5f, 0.5f)
            prepare()
        }
        totalTime = mp.duration
        initPositionBar()
    }

    private fun initPositionBar() {
        bookViewFragmentBinding.mediaPosition.max = totalTime

        launch {
            setTimeOnProgressBar()
        }
    }

    private suspend fun setTimeOnProgressBar() {
        coroutineScope {
            launch {
                var progress = mp.currentPosition
                while (progress < mp.duration) {
                    progress = mp.currentPosition
                    bookViewFragmentBinding.mediaPosition.progress = progress
                    val timePlayed = progress
                    val timeLeft = mp.duration - timePlayed
                    bookViewFragmentBinding.timePlayed.text = formatIntToTime(timePlayed)
                    bookViewFragmentBinding.timeLeft.text =
                        getString(R.string.time_left, formatIntToTime(timeLeft))
                    delay(1000)
                }
            }
        }
    }
}

Answer 1

这看起来是正确的，但是您在循环周围创建了两个不必要的协程层。在 setTimeOnProgressBar() 中，您已将协程包装在一个新的 coroutineScope 中，但您不将其用于任何用途。可以将其删除，然后这根本就不必是挂起函数。因此，您还可以删除在 initPositionBar() 中包装对 setTimeOnProgressBar() 的调用的协程。

此外，您还重新创建了 Android ktx 库已提供的一堆样板。已经有一个 lifecycleScope 扩展属性可用于启动协程，并且它会在 onDestroyView() 中自动取消。因此，您不需要创建父作业或覆盖 coroutineContext，或取消父作业。

启动协程时可以使用lifecycleScope.launch。

class BookViewFragment : Fragment() {
    private var _binding: FragmentBookViewerBinding? = null
    private val bookViewFragmentBinding get() = _binding!!

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        _binding = FragmentBookViewerBinding.inflate(layoutInflater)
        val view = bookViewFragmentBinding.root
        initMediaPlayer()
        return view
    }

    override fun onDestroyView() {
        super.onDestroyView()
        _binding = null
        mp.stop()
        mp.release()
    }

    private fun initMediaPlayer() {
        mp = MediaPlayer()

        mp.run {
            setDataSource(...)
            setVolume(0.5f, 0.5f)
            prepare()
        }
        totalTime = mp.duration
        initPositionBar()
    }

    private fun initPositionBar() {
        bookViewFragmentBinding.mediaPosition.max = totalTime

        setTimeOnProgressBar()
    }

    private fun setTimeOnProgressBar() {
        lifecycleScope.launch {
            var progress = mp.currentPosition
            while (progress < mp.duration) {
                progress = mp.currentPosition
                bookViewFragmentBinding.mediaPosition.progress = progress
                val timePlayed = progress
                val timeLeft = mp.duration - timePlayed
                bookViewFragmentBinding.timePlayed.text = formatIntToTime(timePlayed)
                bookViewFragmentBinding.timeLeft.text =
                        getString(R.string.time_left, formatIntToTime(timeLeft))
                delay(1000)
            }
        }
    }
}