对于组合框，如果考虑一下，这是一个奇怪的要求.难怪System.Windows.Forms没有这样的功能.无论如何，请参见此CodeProject文章:
具有只读行为的组合框 [

For a combo box, this is a strange requirement, if you think about it. No wonder, there is no such feature if System.Windows.Forms. Anyway, please see this CodeProject article:
ComboBox with read only behavior[^].

—SA

术语只读"的使用令人困惑.如果您的目的是防止用户编辑文本，请使用DropDownStyle DropDownList.

请参见 ComboBoxStyle [

The use of the term readonly is confusing. If your aim is to prevent the user editing the text then use the DropDownStyle DropDownList.

See ComboBoxStyle[^]

Alan.

hii，
类似的线程是

只读ComboBox [

hii ,
similar thread is

Read only ComboBox[^]