SmsView | SMS view for android | SMS library

That's because you only expand or collapse your views when your ViewHolder are created, and you do not bind them when they are recycled. To fix this issue, you need to bind the views correctly (not in their constructors) in onBindViewHolder method:

Since your getItemViewType is choosing the ViewHolder type reference based in the object instance it is ok to have an empty class. You can achieve this in multiple ways. Personally, I usually use an attribute instead of 5 different Object classes, looks simpler and you will be only dealing with one kind of object.

You would have something like this:

@NonNull is just an IDE flag (and used for Kotlin cross-compatibility). It doesn't do much more than tell the IDE when it should and shouldn't warn you about potential null pointers.

Just because you declare it doesn't mean your method will return a non-null value. Of course, yours will just because of how it works, but the IDE isn't that smart. All it sees is a contradiction: you use the @NonNull parameter, but you also have a case where you return a null value.

The easiest way to fix this would be to just replace your default case with what's under TYPE_EXPANDABLE or TYPE_NONEXPANDABLE and remove the redundant case, ie:

EDIT: From Ben P's comment, it would also be a good idea to throw an Exception in your onCreateViewHolderMethod() if the current View type is unexpected.

Have you added numberOfRowsInSection and what is the value you are passing in it? As per your code, it would need to be like below code