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android - Inappropriate blocking method call, but Suspend function 'withContext' should be called only from a coroutine or another suspend function

问题描述

In my Service, I need to call on onStartCommand some methods that require withContext(Dispatchers.IO) instead CoroutineScope(Dispatchers.IO) like:

But Suspend function 'withContext' should be called only from a coroutine or another suspend function. So if onStartCommand can't be a suspend function because it has override and withContext can't be called by CoroutineScope because Inappropriate blocking method call of methods

                val url = URL(pokemon.linkImage)
                val iS = url.openConnection().getInputStream()

How can I resolve this problem?

My onStartCommand():

override fun onStartCommand(intent: Intent, flags: Int, startId: Int): Int {

    //create the directory on internal storage that will contains all pokemon images
    val path = applicationContext.filesDir.absolutePath
    val dirName = "/pokeimg"
    val dir = File(path, dirName)
    if(!dir.exists())
        dir.mkdir()
    CoroutineScope(Dispatchers.IO).launch {
        //get the list of pokemon when they are loaded from repository
        val listOfPokemon =
            PersistenceSingletonRepository.getInstance(applicationContext).getListOfPokemon()
        //download all the image for each pokemon in the list, but only if the image is
        //not present in the directory
        for(pokemon in listOfPokemon) {
            val imageName = "${pokemon.name}.png"
            val file = File("${dir.absolutePath}/$imageName")
            //check if image not exists on internal storage and if is not an official-artwork
            //images that aren't official-artwork has less quality so don't resize
            if(!file.exists()) {
                //download img
                val url = URL(pokemon.linkImage)
                val iS = url.openConnection().getInputStream()
                val opts = BitmapFactory.Options()
                if (!Utils.isBadImage(pokemon.linkImage)) {
                    //request a smaller image
                    opts.inSampleSize = 2
                }
                val bitmap = BitmapFactory.decodeStream(iS, null, opts)
                val fOut= FileOutputStream(file)

                bitmap?.compress(Bitmap.CompressFormat.PNG, 100, fOut)
                fOut.flush()
                fOut.close()
            }

        }
        stopSelf()
    }
    return START_NOT_STICKY
}

标签： androidkotlinkotlin-coroutinesandroid-context

解决方案

您可以放心地忽略该警告，已知它有很多误报。您在 IO 调度程序中启动了协程，该调度程序是为阻塞调用而设计的。

另一方面，使用CoroutineScope没有父节点和生命周期绑定的 ad-hoc 启动任何东西通常是错误的做法。您应该尊重服务生命周期并在onDestroy. 例如，请参见此处。

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