Tree: nodes initially show + expando icon even when no children

[bill]

When a tree folder is initially displayed, it has the + expando icon even if there are no children. The expando icon is corrected if the user tries to open the node.

Sometimes this is desired behavior, because it's an expensive operation to query if the node actually has children.

However, for the typical dojo.store where the list of children (or a list of references to children) are stored in a attribute, checking if the children attribute exists and contains one or more elements is fast.

The root problem is that dijit.tree.model has a method called mayHaveChildren(), which dijit.Tree is unfortunately using for two separate (conflicting) purposes:

• test if the item is a folder
• test if the item either has children, or may have children but we don't know

The name of the method is also confusing as it could be interpreted to mean that the node may have children in the future (i.e. it's an empty folder, rather than a plain document).

So, mayHaveChildren() in TreeStoreModel could be changed to:

return dojo.some(this.childrenAttrs, function(attr){
	return this.store.hasAttribute(item, attr) &&
                           this.store.getValues(item, attr).length > 0;
}, this);

However, that would break Tree.getIconClass(), causing empty folders to show up as the leaf (piece of paper) icon.

Maybe the solution is to not have any icons in the tree by default, and make users specify a custom getIconClass() method? The alternative is to add another method to the model called isFolder(), but I'm not sure if that should be the responsibility of the model.

(this ticket was split off from #9379)

[bill]

Woops, somehow the title got copied from #9339, fixing it.

[bill]

See also related ticket #17465, about nodes that originally have no children but then they get children later on.

[dylan]

Bill, is this worth keeping open at this point? Or close as patchwelcome?