Do custom ImageLoaders need to manage cache entries themselves?

[treitter]

Hi, I've got a custom ImageLoader class that generates images by composing local images (so creating each is a bit expensive). I noticed that the caching I configured was getting zero cache hits though I created the memoryCache and diskCache. If I manually read and write from the memoryCache in my implementation of ImageLoader::execute(), caching works as expected. Should I be doing this (and add the equivalent for diskCache) or is there infrastructure outside of custom ImageLoaders that is meant to manage these transparently?

Are there any example custom image loaders? I couldn't find any in the source tree or documentation.

Thanks!

[treitter]

I realized there's a test case which answers this question. Yes, there's built-in support for reading and writing from/to disk. My solution, including image compression on disk and converting all the way from/to a Drawable:

// NOTE: as of this writing, this is required:
// @OptIn(ExperimentalCoilApi::class)
inline fun <T : DiskCache.Editor?, R> T.use(block: (T) -> R): R {
    try {
        return block(this).also { this?.commit() }
    } catch (e: Exception) {
        this?.abort()
        throw e
    }
}
    
// NOTE: as of this writing, this is required:
// @OptIn(ExperimentalCoilApi::class)
private fun drawableFromDiskCache(diskCacheKey: String?): Drawable? {
    diskCacheKey ?: return null

    diskCache.openSnapshot(diskCacheKey)?.use { snapshot ->
        val data = diskCache.fileSystem.read(snapshot.data) { readByteArray() }
        val bitmap = BitmapFactory.decodeByteArray(data, 0, data.size)
        return bitmap.toDrawable(context.resources)
    }

    return null
}

// NOTE: as of this writing, this is required:
// @OptIn(ExperimentalCoilApi::class)
private fun storeDrawableInDiskCache(request: ImageRequest, drawable: Drawable) {
    if (!request.diskCachePolicy.writeEnabled) return
    val key = request.diskCacheKey ?: return

    diskCache.openEditor(key)?.use { editor ->
        // NOTE: editor.metadata can be used similarly for arbitrary associated data
        diskCache.fileSystem.write(editor.data) {
            val bitmap = drawable.toBitmap()

            val stream = ByteArrayOutputStream()
            // other image formats are also supported
            //
            // writing the raw bitmap doesn't work for me but PNG is lossless 
            // and much faster overall than raw
            bitmap.compress(Bitmap.CompressFormat.PNG, 100, stream)
            val bytes = stream.toByteArray()
            write(bytes)
        }
    }
}