reverse layout and stack from end throwing error

Question

 private fun initRecyclerView(){
       studentRecyclerView.layoutManager=LinearLayoutManager(this)

        layoutManager.reverseLayout=true
        layoutManager.stackFromEnd=true

        adapter = StudentRecyclerViewAdapter{
            selectedItem:Student -> listitemclicked(selectedItem)
        }
        studentRecyclerView.adapter=adapter
        displayStudentList()
    }

I want to reverse the recycler view, but whenever I use layoutManager.reverseLayout and layoutManager.stackFromEnd these lines throw an error.

I don't know what to do.

Could you start by editing your post to include what error you have? — xihtyM, Mar 20 '23 at 14:34
Also, this is just guesswork, but shouldn't `layoutManager` be `studentRecyclerView.layoutManager`? — xihtyM, Mar 20 '23 at 14:41
this reverselayout and stackFromEnd could be used with the variable name but i do not know what is variable name in this beacuse i do not declare any variable of layout manager above — , Mar 20 '23 at 14:44
Try [this](https://stackoverflow.com/questions/46168245/recyclerview-reverse-order). — xihtyM, Mar 20 '23 at 14:57

score 0 · Accepted Answer · answered Mar 20 '23 at 22:59

setReverseLayout and setStackFromEnd are both functions on the LinearLayoutManager class, not the base LayoutManager one. So you have to make sure the variable you're referencing has a LinearLayoutManager type (or cast it):

// implicitly setting the type to the class you're constructing
val layoutManager = LinearLayoutManager(this)

// or you can just specify it explicitly
val layoutManager: LinearLayoutManager = LinearLayoutManager(this)

// now you can configure that object, and set it on the RecyclerView
layoutManager.setReverseLayout(true)
studentRecyclerView.layoutManager = layoutManager

studentRecyclerView.layoutManager's type is just the base LayoutManager (so you can provide different implementations of a layout manager), so if you read that property you'll just get a LayoutManager. If you wanted to treat it as a LinearLayoutManager specifically (and access the functions and properties on that type), you'd have to cast it:

studentRecyclerView.layoutManager = LinearLayoutManager(this)
...
(studentRecyclerView.layoutManager as LinearLayoutManager).setReverseLayout(true)

This is messy though, and it's usually better to just hold your own reference with the correct type - no need to complicate things, especially during a simple setup block!

And because it's Kotlin, set* functions can be written as a property (e.g. layoutManager.reverseLayout = true) and the IDE will offer to change the function version to the property version, if appropriate. Same thing though, just a different way of writing it.

reverse layout and stack from end throwing error

1 Answers1