Thank you Xrystal, I'll check that.
Here is the full addon :
https://github.com/zulunovembre/Merchant/tree/dev
The current branch is "dev"
I've also added it as file attachment to this reply.
You have to open your bank once to fill the stockpile table.
The code calling Merchant.UI.DrawStockpileGrid is in Stockpile.lua, in function Merchant.UI.DrawStockpile, which is called by the three dropdown handlers Merchant.UI.Stockpile[Chars,Display,Filters]DropDownHandler. DrawStockpile is also called in the OnShow event handler of the global panel, in UI/Main.lua in Merchant.UI.Create function