Yes, I admit it, the DropDownChoice is tough!
After spending way too many hours on it, I have the following advice. If you are trying to bind the value of your dropdownchoice to anything besides a String, that's fine and dandy, but don't try to have the DropDownChoice bind DIRECTLY to your value. For example, if you have a Double, Long, whatever, you should set it yourself. How do you do this? By having the DropDownChoice bind to some pojo, and you use that pojo value to set your Double/Long/Whatever.