Getting value of selected item in list box as string

string textValue = ((ListBoxItem)listBox1.SelectedItem).Content.ToString();

To retreive the value of all selected item in à listbox you can cast selected item in DataRowView and then select column where your data is:

foreach(object element in listbox.SelectedItems) {
    DataRowView row = (DataRowView)element;
    MessageBox.Show(row[0]);
}

If you are using ListBox in your application and you want to return the selected value of ListBox and display it in a Label or any thing else then use this code, it will help you

 private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
         label1.Text  = listBox1.SelectedItem.ToString();
    }

If you want to retrieve the display text of the item, use the GetItemText method:

string text = listBox1.GetItemText(listBox1.SelectedItem);