PositionalDataSource cancelling fetch for loadRange(params: LoadRangeParams, callback: LoadRangeCallback<Songs>) crashes

[AndrewBloom]

What I do:

override fun loadInitial(params: LoadInitialParams, callback: LoadInitialCallback<Songs>) {
    coroutineScope.launch(Dispatchers.IO) {
        val (songs, count) = getSongs(this, params.requestedLoadSize, params.requestedStartPosition)
        callback.onResult(songs, 0, count)
    }
}

So It's with "count" to get those infamous placeholders ....

override fun loadRange(params: LoadRangeParams, callback: LoadRangeCallback<Songs>) {
    //job?.cancel()
    job = coroutineScope.launch(Dispatchers.IO) {
        callback.onResult(mutableListOf<Songs>())
        //callback.onResult(getSongs(this, params.loadSize, params.startPosition).first)
    }
}

Here it would make sense to cancel the coroutine (It's a fetch on the MediaStore) and give back the part of the list loaded, but seems that it doesn't like less elements than what it expects. On the other end what's the point to fill up the list with rubbish if I want to abort the operation and visualise placeholders on the adapter with the suggested technique
if getItem(position)==null then show my beautiful placeholder

As a side note, the fact everyone says that you can't get the count from a contentProvider with "select count(*) from whatever" it's pretty annoying, but that's another story.

ah almost forgot. the stacktrace i get:

2020-06-19 10:42:29.550 23854-23854/com.shapedbyiris.consumer E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.shapedbyiris.consumer, PID: 23854
java.lang.IllegalArgumentException: page introduces incorrect tiling
at androidx.paging.PagedStorage.insertPage(PagedStorage.java:545)
at androidx.paging.PagedStorage.tryInsertPageAndTrim(PagedStorage.java:504)
at androidx.paging.TiledPagedList$1.onPageResult(TiledPagedList.java:60)
at androidx.paging.DataSource$LoadCallbackHelper$1.run(DataSource.java:324)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

Edit#2:
The effect you see without cancelling is that if you scroll like crazy (and I mean real crazy) UI slows down visibly

[AndrewBloom]

Ok, I see this is repo for a codelab not the actual androidx library. I see the loadInitial and loadRange are called on a worker thread so no need to run a coroutine to get the data.

Still wondering why the UI slows down so much in my case... but I get this is not your problem :)
I'll close this.