Anchor contents to bottom

[shaurya947]

I'm using ContourLayout to build a view that will be placed inside a ScrollView (with fillViewport="true"). When scrolling is not required, I'd like for the contents to be anchored to the bottom of the ScrollView.

Here is how I'm going about it (for simplicity, let's just say there are 2 children views):

class MyContourView(
    context: Context,
    private val view1: View,
    private val view2: View,
    private val interItemMarginPx: Int,
    private val lrMarginPx: Int
) : ContourLayout(context) {
    init {
        contourHeightOf { availableHeight ->
            maxOf(availableHeight, view2.bottom() + interItemMarginPx
        }
    }

    override fun onInitializeLayout() {
        view2.applyLayout(
            leftTo { parent.left() + lrMarginPx }.rightTo { parent.right() - lrMarginPx },
            bottomTo { parent.bottom() - interItemMarginPx }
        )

        view1.applyLayout(
            leftTo { parent.left() + lrMarginPx }.rightTo { parent.right() - lrMarginPx },
            bottomTo { view2.top() - interItemMarginPx }
        )
    }
}

But I get a CircularReferenceDetected error (at the line where I call view2.bottom() in contourHeightOf {}). I can see why that's the case: view2 references parent.bottom() and the parent references view2.bottom() in determining its height.

Everything works if I remove the contourHeightOf {} block -- in which case it's always going to be availableHeight. But this breaks the scrolling if the height of the contents is greater than availableHeight.

How do I go about this use case?

[shaurya947]

Temporarily achieved this by wrapping MyContourView inside a ConstraintLayout in my fragment. The ConstraintLayout has a dummy View at the top (a "spacer") that expands to fill the space available to it. Not very satisfied though.. hoping there is a way without nesting ViewGroups like this.

[dimsuz]

I am currently trying to achieve the same and I plan to do it like this:

Let's say my view is split into 2 parts: Main and AnchoredToBottom. If there is no space, than A follows immediately below M, otherwise spacing is added so that A appears to be anchored to the bottom

1. In contourHeightOf: if bottom() - A.height() < M.bottom() then we have an overflow and return A.bottom() else we return it unmodified
2. In A.applyLayout() we also check for overflow and either do A.topTo { M.bottom() } if there is an overflow or do A.topTo { M.bottom() - calculateTopMarginBasedOn(parent.height()) }

What I currently miss here is comparison operators for YInt/XInt, actually I came to file an issue and noticed your report :)

[dimsuz]

Oops, this won't work because there's no way to know bottom() of whole contour layout in contourHeightOf { }...

[aerb]

The problem with the original layout is MyContourLayout has a height that is a function of view2.bottom() and view2.bottom() is a function of MyContourLayout's height.

It's not satisfying but the solution here would be:

contourHeightOf { availableHeight ->
  maxOf(availableHeight, view1.height() + view2.height() + interItemMarginPx)
}