[WPF] Caliburn Micro学习三 Binding

Caliburn Micro学习一 Installation

Caliburn Micro学习二 Infrastructure

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)" />