Custom Combobox-like Control?

[galexy]

I need to create something like a Combobox or DateTimePicker. There is an Edit box where I have to input some value either directly, or I can input some other values in the dropdown control(kind of a dialog that should contain a few labels and editboxes) that shows up after I click a little button next to the editbox and after I click somewhere outside the control, the dropdown control closes up, makes calculation based on input value and displays the calculated value in the original editbox.