Library and just sample support for alternative BitmapLoaders

[yschimke]

Use case description

Apps typically have some image loading library. These libraries may do a few things

1. Cache images to avoid re-requesting
2. Allow customising image loading, such as failure images, or transformations
3. Use existing HTTP clients, including any interceptors, such as enforcing SSL.

Proposed solution

Show an example of using a typical image loader such as Coil.

/*
 * Copyright 2022 Google Inc. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 */

import android.content.Context
import android.graphics.Bitmap
import android.graphics.BitmapFactory
import android.graphics.drawable.BitmapDrawable
import android.net.Uri
import androidx.media3.session.BitmapLoader
import coil.ImageLoader
import coil.request.ErrorResult
import coil.request.ImageRequest
import com.google.common.util.concurrent.ListenableFuture
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.guava.future
import java.io.IOException

class CoilBitmapLoader(
    private val imageLoader: ImageLoader,
    private val context: Context,
    private val coroutineScope: CoroutineScope,
) : BitmapLoader {
    override fun decodeBitmap(data: ByteArray): ListenableFuture<Bitmap> {
        return coroutineScope.future {
            val bitmap = BitmapFactory.decodeByteArray(data,  /* offset= */0, data.size)

            bitmap ?: throw IOException("Unable to decode bitmap")
        }
    }

    override fun loadBitmap(uri: Uri): ListenableFuture<Bitmap> = coroutineScope.future {
        val request = ImageRequest.Builder(context)
            .data(uri)
            .allowHardware(false)
            .build()

        val response = imageLoader.execute(request)
        val bitmap = (response.drawable as? BitmapDrawable)?.bitmap
        bitmap
            ?: throw IOException("Unable to load bitmap " + (response as? ErrorResult)?.throwable)
    }
}

and in MediaSessionService

    override fun onCreate() {
        super.onCreate()

        setMediaNotificationProvider(DefaultMediaNotificationProvider(application, CoilBitmapLoader(
            ImageLoader(this), application, this.lifecycleScope)))
    }

Alternatives considered

This is already possible, feel free to close, or advise if the code above is correct.

[christosts]

Thank you for pointing this. I'm marking the issue as a documentation candidate. I'll try to include a seminal implementation with Glide too.

[christosts]

On your implementation:

• I am not familiar with Coil so I'll take your code is using it as expected, otherwise I don't see a major issue.
• With the next release (beta02/ or rc01, whichever comes first) you will need to use a Builder to build the DefaultMediaNotificationProvider. This was changed in order to support Make channel ID and name configurable in DefaultMediaNotificationProvider #104.
• The library caches the artwork of the last recently shown notification. Every time a new notification must be shown and the media has different artwork (e.g. pressing next on the notification), the library will request to load the media item's artwork. If there is a pending download to a different artwork from a previous notification still on-going, the library will not cancel it, for example via Future.cancel(). It's currently left the BitmapLoader impl to detect if it wants to drop on-going downloads. The default implementation does not drop downloads either (yet). We will put that in the documentation too.