Ok but you never told your Widget to Update if you Pick something up. You just send over whatever there is in your Inventory when you create it. I did not See any Function that Updates your List unless you completly Destroy and recreate the Main Widget nothing will happen if you add items to your Inventory (making the Widget invisible is not enough!)
So do you recreate or Update it in any way? If not it will not Update on its own (adding more Button Widgets)