If you are coming over to Yii 2 from Yii 1.x, you may have already read this useful wiki for creating dependent dropdowns.
You can use a similar approach in Yii 2 to do the same. But if you are looking at a prebuilt solution that helps you manage it easier, read along.
So you want to use CForm (form builder), but need to preload dropdowns in a form? It's simpler than it seems.
You got your CFormModel, CForm and the actual Form, right?
Let's say you have the typical State -> City dependent dropdowns, so you would want to load the from with the State and City selected.
CMenu offers great functionality and the ability to customize just about every aspect of the output. There are many times when I need to create a drop down menu or simply modify the look to make the designers happy. Because this seems to be a common task for me, I figured I would share my code to create a very simple drop down menu that other people could use.