[WPF] Caliburn Micro学习三 Binding

如果说WPF推崇的Binding开辟了一条UI开发新的方式——让写代码的人专注在代码上，让界面设计师去实现界面，他们工作在同一个项目上，使用不同的IDE，最终Build出来真正的产品，那Caliburn Micro无疑是一个加速器，它不仅加速了Binding的使用范畴，还加速了代码的编写速度。

首先，得介绍另外一个Assembly:

xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"

这个Assembly包含在Express Blend SDK里面，Microsoft Download Page：http://www.microsoft.com/en-us/download/details.aspx?id=3062

没有Caliburn.Micro，绑定到一个Event到一个ICommand

        public ICommand CommandDataPathSelectionChanged

        {

            get

            {

                if (_cmd_path_selchged == null)

                    _cmd_path_selchged = new ACRelayCommand(

                        x => OnDataPathSelectionChanged(x)

                            );

                return _cmd_path_selchged;

            }

        }

其中，ACRelayCommand的定义：

 public class ACRelayCommand : ICommand

    {

        #region Fields

        readonly Action<object> _execute;

        readonly Predicate<object> _canExecute;

        #endregion // Fields

        #region Constructors

        /// <summary>

        /// Creates a new command that can always execute.

        /// </summary>

        /// <param name="execute">The execution logic.</param>

        public ACRelayCommand(Action<object> execute)

            : this(execute, null)

        {

        }

        /// <summary>

        /// Creates a new command.

        /// </summary>

        /// <param name="execute">The execution logic.</param>

        /// <param name="canExecute">The execution status logic.</param>

        public ACRelayCommand(Action<object> execute, Predicate<object> canExecute)

        {

            if (execute == null)

                throw new ArgumentNullException("execute");

            _execute = execute;

            _canExecute = canExecute;

        }

        #endregion // Constructors

        #region ICommand Members

        [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);

        }

        #endregion // ICommand Members

    }

而作为对比，使用了Caliburn.Micro，可以直接绑定Event到一个Method

            <ComboBox Name="cmbDataPath" Width="485" ItemsSource="{Binding DataPathList}"

                      SelectedItem="{Binding SelectedDataPath}" >

                <i:Interaction.Triggers>

                    <i:EventTrigger EventName="SelectionChanged">

                        <cal:ActionMessage MethodName="OnSelectionChanged">

                            <cal:Parameter Value="$source" />

                            <cal:Parameter Value="$eventArgs" />

                        </cal:ActionMessage>

                    </i:EventTrigger>

                </i:Interaction.Triggers>

            </ComboBox>

其中，Parameter的Value可以指定如下值：

$eventArgs – EventArgs对象.
$dataContext – UI界面空间的DataContext.
$source – 实际FrameworkElement.
$view - 绑定在ViewModel的View.
$executionContext - 执行上下文.
$this - UIelement 对象.

另外，常用的XAML中绑定语法：

<Button Content="DoSomething"

        cal:Message.Attach="[Event Click] = [Action DoSomething($dataContext)]" />

甚至同时绑定多个Event:

<Button Content="Let's Talk"

        cal:Message.Attach="[Event MouseEnter] = [Action Talk('Hello', Name.Text)]; [Event MouseLeave] = [Action Talk('Goodbye', Name.Text)]" />

简化的语法：

<Button Content="Click Me"

        cal:Message.Attach="SayHello(Name)" />