不适当的阻塞方法调用，但挂起函数“withContext”只能从协程或另一个挂起函数调用

Question

在我的服务中，我需要调用onStartCommand一些需要的方法，withContext(Dispatchers.IO)例如CoroutineScope(Dispatchers.IO)：

• url = URL(pokemon.linkImage)
• url.openConnection().getInputStream()
• fOut= FileOutputStream(文件)
• fOut.flush()
• fOut.close()

但Suspend function 'withContext' should be called only from a coroutine or another suspend function。所以 ifonStartCommand不能是一个挂起函数，因为它具有重写，并且由于方法withContext而不能被 CoroutineScope 调用Inappropriate blocking method call

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

我该如何解决这个问题？

我的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
}

Answer 1

您可以安全地忽略该警告，众所周知它有很多误报。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没有父级且没有生命周期绑定的临时启动任何内容通常是错误的做法。您应该尊重服务生命周期并取消您的协程onDestroy。参见此处的示例。