Display a Combobox control as read-only on Windows Form
You can disable the Combobox so that no data can be entered into the Textbox portion or the list portion of the control as follows:
set comboBox1::Enabled to false
If you want your users to be able to pick from the list but not enter a value in the Textbox then change the dropdownstyle property to dropdownlist.
setcomboBox1::DropDownStyle to type ComboBoxStyle::DropDownList