put this inside your DisplayInfo method: TextBox1.Text = oUser.LoginName
change also clientContext.Load(oUser) with clientContext.Load(clientContext.Web,s=>s.CurrentUser);
ok, sorry. let me rephrase:
1. change clientContext.Load(oUser) with clientContext.Load(clientContext.Web,s=>s.CurrentUser)
2. put this inside your DisplayInfo method: TextBox1.Text = clientContext.Web.CurrentUser.LoginName