private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
    ComboBox cmb = (ComboBox)sender;
    int selectedIndex = cmb.SelectedIndex;
    int selectedValue = (int)cmb.SelectedValue;

    ComboboxItem selectedCar = (ComboboxItem)cmb.SelectedItem;
    MessageBox.Show(String.Format("Index: [{0}] CarName={1}; Value={2}", selectedIndex, selectedCar.Text, selecteVal));        
}

int comboBox_selectedIndex = comboBoxName.SelectedIndex; //item index
string comboBox_selectedContent = comboBoxName.SelectedItem; //item name
// Unselected combo box returns null. Be careful to catch errors.

string getText = comboBox.SelectedItem.ToString();