GencyclerRecyclerAdapter.elements breaks encapsualtion

[Eugen Pechanec]

Current behavior

Currently, elements is var and mutable and public, allowing consumers to bypass the adapter API and completely break it. And new developers especially tend to work with the original ArrayList and then get confused when the RecyclerView doesn't update automatically.

abstract class GencyclerRecyclerAdapter<T : GencyclerModel, VH : GencyclerHolder>(
	var elements: MutableList<T> = ArrayList(),
) : RecyclerView.Adapter<VH>() {

Expected behavior

elements should be private val, so only the adapter can access it and consumers can change it only through the adapter's public API.

abstract class GencyclerRecyclerAdapter<T : GencyclerModel, VH : GencyclerHolder>(
) : RecyclerView.Adapter<VH>() {

    private val elements: MutableList<T> = ArrayList(),

    constructor(elements: List<T>): this() {
        // Make a private copy.
        this.elements.addAll(elements)
    }

[Gil Goldzweig]

I'm not sure about this part. I had cases where sometimes I needed to execute a few actions before I call notify.

[Eugen Pechanec]

Could you give a concrete use case?

[Gil Goldzweig]

There was a case that I needed to add multiple elements but I couldn't use addAll because I received the data as a stream one by one but the UI only needed to be updated after x amount of items.

I used the elements to add the items one by one and after the x amount of items I called notifyItemRangeInserted

[Eugen Pechanec]

The views wouldn't match the elements. The element count wouldn't match the expected state in recycler view and it would crash. Just because the user was scrolling around while all this is happening.

So, you can't alter the adapters data set without letting everybody know there were changes. You can't hope to "fix" some sort of shitty inappropriate upstream API in the adapter. What can be done?

UI only needed to be updated after x amount of items

Alright then, first collect X items and then use addAll. In RxJava2 you would use the buffer operator.

This is doable without breaking encapsulation. In fact, that's a huge red flag that something else (the data source in this case) isn't just right.

[Gil Goldzweig]

Okay, I see your point.