Nodes tree view falsely scrolls on node expansion

[jjac]

Steps to reproduce

This false behavior may happen on two occasions:

• Select a node, scroll down to some other distant node, expand it and the browser will scroll back to the original node
• Make sure no node is selected (e.g. expand and collapse a node that is the direct ancestor of a selected node). Then scroll down to some other distant node, expand it and the browser will scroll to the direct ancestor of the expanded node - possibly scrolling the just expanded node out of the visible area.

Expected behavior

When expanding a node the scroll position of the surrounding view should stay in the area so that the user can watch the effect of the expansion.

Code Analysis

The first behavior mentioned is due to a side effect of selectNode: which will be called when the expanded state is restored in

-[IMBNodeViewController _nodesDidChange]

The second behavior mentioned is due to a side effect of a recent change in

-[IMBLibraryController _replaceNode:withNode:parentNodeIdentifier:]

in which a workaround was implemented to avoid a 'nasty crashing bug' (see lines 710ff):

[parentNode setSubNodes:nil];       // Important workaround. Do not remove!

This workaround causes the NSOutlineView to scroll to parentNode.

Suggested Fix

After aeons of analyzing the control flow involved I found the fix to be a simple save/restore pattern of the current scroll position (to be inserted at the right places). I intend to deliver the fix along with the upcoming Photo Stream pull request.