C ＃ listbox how to get the selected content (search many invalid articles)

string info= ( listTalk.SelectedValue as TextBlock ).Text.ToString().Trim();

Do not use SelectedItem

as The control type after is filled in according to the actual situation , If you don't know , First, the output listTalk.SelectedValue.Tostring()

The operation after obtaining the control is also filled in according to the actual situation