CODEWITHSUNDEEP
cocoatreeviewlazy-loadingfindernsoutlineview
Yeung
Yeung

Reputation: 11

Implement a Finder-like treeview and representing its nodes with lazy loading using NSOutlineview

When implement a big file system tree in NSOutlineview, it lacks an event notification when user click the left side down arrow triangle icon of a node. This is very important when lazy-loading a large amount of file nodes into a directory node and represent it into NSOutlineview. Otherwise, developer have to load entire directory into it, in this way, the loading will force end user to wait, this is not acceptable. In short, current version of NSOutlineview can't implement lazy-loading caused by this issue. Does anyone meet this issue or have an alternative solution to implement a Finder-like treeview with Cocoa NSOutlineview, any help will be great appreciate.

In Addition:

NSOutlineview does not emit an outlineViewItemWillExpand event when click the icon, and there still lacks enough info to get which node will expand even that event emitted, [NSOutlineview selectedRow] can't work because the node which will be expanded have not been selected yet.

Upvotes: 0

Views: 220

Answers (1)

Giles
Giles

Reputation: 1667

I load my child nodes in the following call in NSOutlineViewDataSource:

func outlineView(_ outlineView: NSOutlineView, isItemExpandable item: Any) -> Bool {
        guard let node = item as? Node else { return false }
        return node.children.count > 0
    }

The children property of my Node class is lazy, and hence forced to load here.

This method is only called on Nodes that are visible in the outliner. This way you are only loading one layer ahead of the visible tree. The disclosure triangle (expand arrow) will then be visible if children exist.

If you have an efficient way to know the number of children a node has without actually loading them, then it may be better just to return the child count in outlineView(_: isItemExpandable:) and then do the actual load in outlineViewItemWillExpand(_:) as Willeke has suggested in the comments.

Upvotes: 1

Related Questions