C#

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
       {
           using (var db = new momdbDataContext(Properties.Settings.Default.Remote))
           {



               var aAuthor = (from a in db.Authors
                              where a.ID == (int)comboBox1.SelectedValue
                              select a).FirstOrDefault();
               authorFirstTextBox.Text = aAuthor.AuthorFirst.ToString().Trim();
               authorLastTextBox.Text = aAuthor.AuthorLast.ToString().Trim();
           }

public class RelayCommand : ICommand
{
    readonly Action<object> _execute;
    readonly Predicate<object> _canExecute;        

    public RelayCommand(Action<object> execute)
    : this(execute, null)
    {
    }

    public RelayCommand(Action<object> execute, Predicate<object> canExecute)
    {
        if (execute == null)
            throw new ArgumentNullException("execute");

        _execute = execute;
        _canExecute = canExecute;           
    }

    [DebuggerStepThrough]
    public bool CanExecute(object parameter)
    {
        return _canExecute == null ? true : _canExecute(parameter);
    }

    public event EventHandler CanExecuteChanged
    {
        add { CommandManager.RequerySuggested += value; }
        remove { CommandManager.RequerySuggested -= value; }
    }

    public void Execute(object parameter)
    {
        _execute(parameter);
    }
}