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How to replace AsynTask with RxJava in this case

I have a class that goes to decrease the image but I’m currently on AsyncTask, now I want to replace it because AsyncTask is now deprecated.So can someone help me out with a workaround

Here is my code:

class DecreaseImageTask(
    val uri: Uri? = null,
    val bitmap: Bitmap? = null,
    var context: Context,
    var listener: (String?) -> Unit
) : AsyncTask<Void, Long, String?>() {

    override fun doInBackground(vararg params: Void?): String? {
        return when {
            uri != null -> {
                decreaseImageSize(imagePath = FileUtils.getPathURI(context, uri) ?: "")
            bitmap != null -> {
                decreaseImageSize(bitmap = bitmap)

    override fun onPostExecute(result: String?) {


You could change your decreaseImageSize to accept a callback as a parameter.
In this case, the function will no longer need to return a string, which is passed as a parameter to the callback function and then used as a parameter in its body:

fun decreaseImageSize(imagePath: String? = null, bitmap: Bitmap? = null, callback: (String) -> Unit) {

    val result = "" // The result of the previous decreaseImageSize function


Then, instead of calling the AsyncTask use the new decreaseImageSize function:

    decreaseImageSize(imagePath = FileUtils.getPathURI(context, uri) ?: "") { result -> 
        // Execute the code after the image is decreased

    decreaseImageSize(bitmap = bitmap) { result -> 
        // Execute the code after the image is decreased