Kotlin协程CalledFromWrongThreadException

Question

I'm trying to use Kotlin coroutines to make some heavy job runs in the background.

But I got this error message,

'android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.'

fun setList() {
    media_image_list.adapter = imageListAdapter
    ...

    launch {
        val images = getImages(galleryPath)
        imageListAdapter.setItems(images)
    }
}




suspend private fun getImages(): MutableList<Image> {
    val uri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI
    ...
}

How to make it run in background correctly?

Answer 1

I would suggest to address it in the following way:

First, explicitly offload your "heavy job" into background threads using withContext function like this:

// explicitly request it to be executed in bg thread
suspend private fun getImages(): MutableList<Image> = withContext(CommonPool) {
    val uri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI
    ...
}

Then, always run the coroutines that touch the views or other UI objects in UI thread:

launch(UI) {
    val images = getImages(galleryPath)
    imageListAdapter.setItems(images)
}