WPF supports ComboBox controls bound to commands

The ComboBox and ListBox controls do not implement the icommandsource interface, so command binding in XAML is not supported. The following code implements the icommandsource interface for ComboBox:

public class ComboBoxWithCommand : ComboBox, ICommandSource{    private static EventHandler canExecuteChangedHandler;    public static readonly DependencyProperty CommandProperty = DependencyProperty.Register("Command",                                                                                            typeof(ICommand),                                                                                            typeof(ComboBoxWithCommand),                                                                                            new PropertyMetadata((ICommand)null,                                                                                            new PropertyChangedCallback(CommandChanged)));    public ICommand Command    {        get        {            return (ICommand)GetValue(CommandProperty);        }        set        {            SetValue(CommandProperty, value);        }    }    public static readonly DependencyProperty CommandTargetProperty = DependencyProperty.Register("CommandTarget",                                                                                                  typeof(IInputElement),                                                                                                  typeof(ComboBoxWithCommand),                                                                                                  new PropertyMetadata((IInputElement)null));    public IInputElement CommandTarget    {        get        {            return (IInputElement)GetValue(CommandTargetProperty);        }        set        {            SetValue(CommandTargetProperty, value);        }    }    public static readonly DependencyProperty CommandParameterProperty = DependencyProperty.Register("CommandParameter",                                                                                                     typeof(object),                                                                                                     typeof(ComboBoxWithCommand),                                                                                                     new PropertyMetadata((object)null));    public object CommandParameter    {        get        {            return (object)GetValue(CommandParameterProperty);        }        set        {            SetValue(CommandParameterProperty, value);        }    }    public ComboBoxWithCommand() : base() { }    private static void CommandChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)    {        ComboBoxWithCommand cb = (ComboBoxWithCommand)d;        cb.HookUpCommand((ICommand)e.OldValue, (ICommand)e.NewValue);    }    private void HookUpCommand(ICommand oldCommand, ICommand newCommand)    {        if (oldCommand != null)        {            RemoveCommand(oldCommand, newCommand);        }        AddCommand(oldCommand, newCommand);    }    private void RemoveCommand(ICommand oldCommand, ICommand newCommand)    {        EventHandler handler = CanExecuteChanged;        oldCommand.CanExecuteChanged -= handler;    }    private void AddCommand(ICommand oldCommand, ICommand newCommand)    {        EventHandler handler = new EventHandler(CanExecuteChanged);        canExecuteChangedHandler = handler;        if (newCommand != null)        {            newCommand.CanExecuteChanged  = canExecuteChangedHandler;        }    }    private void CanExecuteChanged(object sender, EventArgs e)    {        if (this.Command != null)        {            RoutedCommand command = this.Command as RoutedCommand;            // If a RoutedCommand.            if (command != null)            {                if (command.CanExecute(this.CommandParameter, this.CommandTarget))                {                    this.IsEnabled = true;                }                else                {                    this.IsEnabled = false;                }            }            // If a not RoutedCommand.            else            {                if (Command.CanExecute(CommandParameter))                {                    this.IsEnabled = true;                }                else                {                    this.IsEnabled = false;                }            }        }    }    protected override void OnSelectionChanged(SelectionChangedEventArgs e)    {        base.OnSelectionChanged(e);        if (this.Command != null)        {            RoutedCommand command = this.Command as RoutedCommand;            if (command != null)            {                command.Execute(this.CommandParameter, this.CommandTarget);            }            else            {                ((ICommand)Command).Execute(CommandParameter);            }        }    }}

In this way, you can bind the command in XAML to process the selectedchanged event of ComboBox!