Kotlin 协程在 Android 中的使用

Question

I'm trying to use Kotlin Coroutines for better performance.

But I'm not sure is it the correct way to use it, so I'd like to have experts review.

After taking a photo with camera, the screen is the blackout for half second while the image processing I guess.

The original code was,

fun uploadPhoto(data: Intent): Observable<Response> {
    val bitmap = data.extras.get("data") as Bitmap
    val bytes = ByteArrayOutputStream()
    bitmap.compress(Bitmap.CompressFormat.JPEG, 100, bytes)

    val baseDir = Environment.getExternalStorageDirectory()
    val file = File(baseDir, Calendar.getInstance().timeInMillis.toString() + ".jpg")
    val fileOutputStream = FileOutputStream(file)
    fileOutputStream.write(bytes.toByteArray())
    fileOutputStream.close()


    return uploadMedia(file)
}

and after I read this tutorial,https://kotlinlang.org/docs/tutorials/coroutines-basic-jvm.html

I changed it to,

fun uploadPhoto(data: Intent): Observable<Response> {
    val baseDir = Environment.getExternalStorageDirectory()
    val file = File(baseDir, Calendar.getInstance().timeInMillis.toString() + ".jpg")

    launch {
        val bitmap = data.extras.get("data") as Bitmap
        val bytes = compressBitMap(bitmap).await()
        val fileOutputStream = FileOutputStream(file)
        fileOutputStream.write(bytes.toByteArray())
        fileOutputStream.close()
    }

    return uploadMedia(file)
}

private fun compressBitMap(bitmap: Bitmap) = async(CommonPool) {
    val bytes = ByteArrayOutputStream()
    bitmap.compress(Bitmap.CompressFormat.JPEG, 100, bytes)
    return@async bytes
}

But I don't see any difference.

What I want to do thing is, I want to run Compressing Bitmap and fileOutputStream jobs in Background to prevent bothering MainThread.

Does it make the better performance?

Answer 1

Coroutines are executed in "CoroutineContexts", you appear to be using an older version of the libs, in newer versions you should always specify the context by using launch(UI) or launch(CommonPool). I don't know by default which context is your "launch" using, but I guess is UI. If that's correct, you are in deed waiting in the UI thread for the compressBitMap completion, blocking the UI thread (A pointless coroutine use)

Try to use launch(CommonPool) instead and see if the magic happens.