WPF中的EventTrigger和命令绑定

在上一篇《使用MVVM模式开发自定义UserControl》中，有一个重要的补充内容，就是WPF中的EventTrigger和命令绑定，在本篇中继续阐述。

如果单纯在Button中使用命令绑定，则其本身就带有Command属性，但是扩展到任何其它控件，就得稍微复杂一点。以本篇来讲，依赖于我们拥有如下两个dll：

Microsoft.Expression.Interactions.dll

System.Windows.Interactivity.dll

这两个dll在装完毕expression blend后会出现在引入列表中。不过，即便我们没有装blend，也可以直接从其它地方COPY过来。在本例中，它们就存在于输出目录中。

1：实现一个behavior

为了在前台中和EventTrigger配合，必须创建一个我们自己的behavior，代码如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Interactivity;
using EventTrigger = System.Windows.Interactivity.EventTrigger;
using System.Windows;
using System.Windows.Input;
namespace WpfControls.Command
{
    [DefaultTrigger(typeof(UIElement), typeof(EventTrigger), "MouseLeftButtonDown")]
    public class ExecuteCommandAction : TargetedTriggerAction<UIElement>
    {
        /// <summary>
        /// Dependency property represents the Command of the behaviour.
        /// </summary>
        public static readonly DependencyProperty CommandParameterProperty = DependencyProperty.RegisterAttached("CommandParameter",
        typeof(object), typeof(ExecuteCommandAction), new FrameworkPropertyMetadata(null));
        /// <summary>
        /// Dependency property represents the Command parameter of the behaviour.
        /// </summary>
        public static readonly DependencyProperty CommandProperty = DependencyProperty.RegisterAttached("Command", typeof(ICommand), typeof(ExecuteCommandAction), new FrameworkPropertyMetadata(null));
        /// <summary>
        /// Gets or sets the Commmand.
        /// </summary>
        public ICommand Command
        {
            get
            {
                return (ICommand)this.GetValue(CommandProperty);
            }
            set
            {
                this.SetValue(CommandProperty, value);
            }
        }
        /// <summary>
        /// Gets or sets the CommandParameter.
        /// </summary>
        public object CommandParameter
        {
            get
            {
                return this.GetValue(CommandParameterProperty);
            }
            set
            {
                this.SetValue(CommandParameterProperty, value);
            }
        }
        /// <summary>
        /// Invoke method is called when the given routed event is fired.
        /// </summary>
        /// <param name=”parameter”>
        /// Parameter is the sender of the event.
        /// </param>
        protected override void Invoke(object parameter)
        {
            if (this.Command != null)
            {
                if (this.Command.CanExecute(this.CommandParameter))
                {
                    this.Command.Execute(this.CommandParameter);
                }
            }
        }
    }
}

2：前台代码

有了上面的这个behavior类型，我们可以在前台如下使用：

3：VM部分代码

public class StudentViewModel : NotificationObject
{
    public StudentViewModel()
    {
        Clicked = new ActionCommand(this.Click);
    }
 
    public ICommand Clicked { get; private set; }
 
    public void Click(object arg)
    {
        //为了演示需要，在这里用了一个MessageBox
        //应尽量避免在VM中揉杂UI交互功能
        MessageBox.Show((arg as Student).StudentName);
    }
}