How to add an item to the list of combobox ?

There are one combobox and two button in my IO page, one button named "AddItem",the other named "DelItem".
The "DelItem" work good, but "AddItem" make the progeam abort.

Somebody help me.
plz.

Hello

add:
ReadINIStr $R3 $PLUGINSDIR\test.ini "Field 1" "State"
GetDlgItem $1 $0 1200
SendMessage $1 ${CB_ADDSTRING} 0 "STR:$R3"
abort

Best Regards

Thank you very much!

You also need !define CB_ADDSTRING 0x0143

-Stu