With a hot observable

ImageRepository.kt

package com.shaishavgandhi.rxreplayingsharesample

import android.content.res.Resources
import android.graphics.Bitmap
import android.graphics.BitmapFactory
import android.util.Log
import androidx.annotation.RawRes
import io.reactivex.Observable
import io.reactivex.subjects.BehaviorSubject

class ImageRepository(private val resources: Resources) {

    companion object {
        private const val TAG = "ImageRepository"
    }

    private val subject = BehaviorSubject.create<Int>()

    private val imageObservable = subject
        .map {
            // We log to make sure we know we're not repeating expensive operations. 
            Log.d(TAG, "Performing expensive operation")
            return@map BitmapFactory.decodeStream(resources.openRawResource(it))
        }

    fun image(): Observable<Bitmap> {
        return imageObservable
    }

    fun loadImage(@RawRes imageId: Int) {
        subject.onNext(imageId)
    }
}