LabVIEW
Darren's Weekly Nugget 03/29/2010
When helping one of my colleagues in LabVIEW R&D with some tree control issues last week, he was surprised to learn that there is a built-in sorting method for tree items:
When using the Edit Tree Items.Sort Children method with the configuration above, all the children of 'parent' (including nested children) will be sorted alphabetically, and case-insensitive. If you want to sort your entire tree in this manner, you would simply wire an empty string to the Tag parameter.
But what about more complicated sorting? There might be cases where you need to sort tree items on something other than, or in addition to, their alphabetical order. For example, take a look at the VI Analyzer Results Window:
As you can see, the high-ranked tests are at the top of the list, the low-ranked tests are at the bottom, and all tests are sorted alphabetically within each category. As you might suspect, the built-in tree sorting method does not allow us to sort based on multiple criteria like this. There is, however, a VI that ships with LabVIEW that allows us to define our own custom sorting VI for tree elements. Here it is:
With Tree Sorter.vi, you provide similar inputs (tree reference, Sort Children?, Reverse?, and tag) that you do for the built-in method, but notice you also provide a Sort Spec VI. This is a VI that you write that defines the sorting rules for the tree. Let's take a look at the Sort Spec VI for the VI Analyzer Results Window I showed above:
As you can see, the Sort Spec VI takes in two tags, and outputs which of those tags should be above the other in sort order. So all you need to provide is logic that will determine which of two arbitrary tags should appear above the other one once your tree is sorted. As you can see, my logic compares the glyphs of the two tags first, and only if they are equal does it use alphabetical ordering to determine the sort order. The real value of Tree Sorter.vi to me is that I only needed to write the sorting rule itself, and I didn't need to write all the code that went through the entire tree and applied the sorting rule.
