Problem Description
I have been trying to create a dynamic layout in QGIS, such that the only parameter changing is the scale, and page width, map width, scalebar position, etc. are determined automatically. I am using the following expression to first find the lowest visible layer, of which I then extract the extent. Then I finally compute the layout size given the scale and extent.
(xmax(layer_property(array_last(array_filter( @layer_ids, is_layer_visible(@element) )), 'extent')) -
xmin(layer_property(array_last(array_filter( @layer_ids, is_layer_visible(@element) )), 'extent')))
* 1000 / round(@map_scale)
When using the expression on a Map Item, it works like a charm. But once I try to apply the same to the dimensions of the Page, the expression returns NULL. Similarly, for a Scalebar item, the expression fails to automatically return the correct coordinates. I have traced the error to the subexpression array_filter( @layer_ids, is_layer_visible(@element)), which returns an empty array.
Questions
Is this intended behavior due to some environment variables changing, and/or is there a fundamental misunderstanding of how expressions work in QGIS? Is there a workaround to still achieve what I am trying to do?
