B4A Library [B4X] Trie based search dialog


This started as an educational project but it can be useful in some cases.
Trie is an interesting data structure that allows fast lookup of prefix matches. It is a tree of prefixes.


Source: https://en.wikipedia.org/wiki/Trie

In the B4X implementation, each node holds a character, a list of child nodes and a list of full values. The tree depth is configurable and in most cases it should be 2 or 3.
The child nodes are sorted. This later allows us to quickly find the path in the tree using binary search.
The items list is expected to be sorted in ascending order. This allows to build the tree very fast. It takes about 45 milliseconds to build a tree made of 37,500 items on my Android device.

The example project builds a trie from a list of cities. Database source: https://simplemaps.com/data/world-cities
The trie is implemented in a separate class and can be used without the search template.

While testing it on B4i, I've encountered a strange issue that required deep investigation. B4i uses the default sorting and string comparison options. I'm not sure whether it is a bug or not (in the underlying framework) but it doesn't sort non-ascii characters as expected.
The solution is to add a flag to these methods. It will be implemented in the next version of B4i.


  • Project.zip
    356.5 KB · Views: 688
Last edited: