c# - Focus on the first element of the list view control WPF -

i have list view control in xaml file. i'm having textblock , dropdown field inside list view. data coming database. want focus on first dropdown. focus not coming there. if press tab focus coming. list view inside groupbox.

if combobox's name "_drop" hope these 2 line can you:

<combobox x:name="_drop"     selectedindex="0"     tabindex="0"/>