combobox's text show nothing , in WPF popup

Question

Hello

I am new in WPF  programming .

my code has a datagrid, when right click a row , a menu appear, then click a message again,  a pop up appear with a combobox on it .

my problem is that the combobox is binding to a string list , when I click the combobox, the dropdown list appear , but no matter I select what, the text of the combobox keep nothing .

 

if I test the combobox in my new small test application , it works fine .

so I guess there are something blocking the selected item to show up?

 

any one has experience ? answer please.

thanks in advance.

 

F