WPF實現支援Command綁定的ComboBox控制項

由於ComboBox，ListBox等控制項沒有實現ICommandSource介面，所以不支援在XAML中進行Command綁定，下面的一段代碼就是，對ComboBox實現對ICommandSource介面的實現：

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);            }        }    }}

如此，便可以在XAML中對Command進行綁定，處理ComboBox的SelectedChanged事件！