ViewModel and Data Binding: why do the views randomly jumble up?

[lunax]

On page 394 I read that:

This is happening because your layout has no way of knowing that you updated SoundViewModel's Sound inside SoundHolder.bind(Sound)

I don’t quite understand why. Following the logic of RecyclerView, every time it needs to recycle a view, onBindViewHolder(), bind(), getItemCount() get called. When bind() is called, we proceed to set the updated sound object to our ViewModel: getViewModel().setSound(sound). We even call executePendingBindings() to force the layout to immediately update itself.

Why then is this logic working when creating views but it breaks once recycling them?

[Srinath]

I too have the same question. In fact, on my Android physical device, I do not see anything like the Figure 20.12 titled Déjà vu. The RecyclerView seems to be working fine for me. Have you found a scenario similar to what was mentioned in the book, yet?

@cstewart your input on this would be great. Thanks!

[Srinath]

Actually, I found the answer by @cstewart in the below posts on the main page for this chapter. The link is pasted below:

Not seeing written behavior on page 394 using APIs above 19

Ah. OK, I see what you are saying. It’s possible that there has been some change in the RecyclerView or DataBinding library where this particular issue no longer shows up. It could also be a factor of how many items are in the list and the screen size. Either way, it continues to be very important that you use BaseObservable and notifyChange when you change the data in a view model. Otherwise, the view model can’t know when to refresh the view. So, it may not be an issue in this case, but it wi…