Viewers not removed from internal list after closing

[petebankhead]

When using multiple viewers, these are stored in an internal list, accessible with

QuPathGUI.getInstance().getViewers()

However, whenever viewers are closed and removed, they remain within the list - when the expectation is that they would be removed. It can be hard to distinguish between viewers that are 'still there' and ones that are not, but the following code does so:

def viewers = qupath.getViewers().collect() // Original list is unmodifiable... so collect
println("Number of viewers: " + viewers.size())

// Remove viewers that are unattached to any scene
viewers.removeAll { it.getView().getScene() == null }
println("Number of viewers attached to scene: " + viewers.size())

In any case, for most users and most uses of QuPath, this does not matter.

Nevertheless, it can cause trouble when scripting with multiple viewers and is a bug that should be fixed.

(Bug encountered and described here)