MVVM中轻松实现Command绑定（五）获取事件参数EventArgs（2）

MVVM中轻松实现Command绑定（五）获取事件参数EventArgs（2）

分类： C# WPF Command EventArgs ViewModel MVVM 2011-08-11 20:48 4375人阅读 评论(9) 收藏 举报

commandbindingbutton扩展nullobject

在上一节中我介绍了“MVVM中轻松实现Command绑定（四）获取事件参数EventArgs”，通过Loaded事件传递控件对象，然后添加事件方法，这样做是可以的，但是不符合MVVM的思想，今日我介绍另一种方法，通过扩展interactivity的InvokeCommandAction来实现事件参数传递。

先来看普通的InvokeCommandAction方式

<Window x:Class="EventArgsInViewModel.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
        xmlns:loc="clr-namespace:EventArgsInViewModel"
        Title="MainWindow" Height="350" Width="525">
    <Window.DataContext>
        <loc:MainWindowViewModel />
    </Window.DataContext>
    <Grid>
        <Button Content="Button" Height="38" HorizontalAlignment="Left" Margin="50,52,0,0" Name="button1" VerticalAlignment="Top" Width="138">
            <i:Interaction.Triggers>
                <i:EventTrigger EventName="Click">
                    <i:InvokeCommandAction
                        Command="{Binding ClickCommand}" CommandParameter="{Binding ElementName=button1}" />
                </i:EventTrigger>
            </i:Interaction.Triggers>
        </Button>
    </Grid>
</Window>

现在为了扩展CommandParameter，定义ExCommandParameter类

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;

namespace EventArgsInViewModel {
    /// <summary>
    /// 扩展CommandParameter，使CommandParameter可以带事件参数
    /// </summary>
    public class ExCommandParameter {
        /// <summary>
        /// 事件触发源
        /// </summary>
        public DependencyObject Sender { get; set; }
        /// <summary>
        /// 事件参数
        /// </summary>
        public EventArgs EventArgs { get; set; }
        /// <summary>
        /// 额外参数
        /// </summary>
        public object Parameter { get; set; }
    }
}

然后定义ExInvokeCommandAction类，用于扩展InvokeCommandAction

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Interactivity;
using System.Windows.Input;
using System.Reflection;

namespace EventArgsInViewModel {
    /// <summary>
    /// 扩展的InvokeCommandAction
    /// </summary>
    public class ExInvokeCommandAction : TriggerAction<DependencyObject> {

        private string commandName;
        public static readonly DependencyProperty CommandProperty = DependencyProperty.Register("Command", typeof(ICommand), typeof(ExInvokeCommandAction), null);
        public static readonly DependencyProperty CommandParameterProperty = DependencyProperty.Register("CommandParameter", typeof(object), typeof(ExInvokeCommandAction), null);
        /// <summary>
        /// 获得或设置此操作应调用的命令的名称。
        /// </summary>
        /// <value>此操作应调用的命令的名称。</value>
        /// <remarks>如果设置了此属性和 Command 属性，则此属性将被后者所取代。</remarks>
        public string CommandName {
            get {
                base.ReadPreamble();
                return this.commandName;
            }
            set {
                if (this.CommandName != value) {
                    base.WritePreamble();
                    this.commandName = value;
                    base.WritePostscript();
                }
            }
        }
        /// <summary>
        /// 获取或设置此操作应调用的命令。这是依赖属性。
        /// </summary>
        /// <value>要执行的命令。</value>
        /// <remarks>如果设置了此属性和 CommandName 属性，则此属性将优先于后者。</remarks>
        public ICommand Command {
            get {
                return (ICommand)base.GetValue(ExInvokeCommandAction.CommandProperty);
            }
            set {
                base.SetValue(ExInvokeCommandAction.CommandProperty, value);
            }
        }
        /// <summary>
        /// 获得或设置命令参数。这是依赖属性。
        /// </summary>
        /// <value>命令参数。</value>
        /// <remarks>这是传递给 ICommand.CanExecute 和 ICommand.Execute 的值。</remarks>
        public object CommandParameter {
            get {
                return base.GetValue(ExInvokeCommandAction.CommandParameterProperty);
            }
            set {
                base.SetValue(ExInvokeCommandAction.CommandParameterProperty, value);
            }
        }
        /// <summary>
        /// 调用操作。
        /// </summary>
        /// <param name="parameter">操作的参数。如果操作不需要参数，则可以将参数设置为空引用。</param>
        protected override void Invoke(object parameter) {
            if (base.AssociatedObject != null) {
                ICommand command = this.ResolveCommand();

                /*
                 * ★★★★★★★★★★★★★★★★★★★★★★★★
                 * 注意这里添加了事件触发源和事件参数
                 * ★★★★★★★★★★★★★★★★★★★★★★★★
                 */
                ExCommandParameter exParameter = new ExCommandParameter {
                    Sender=base.AssociatedObject,
                    Parameter = GetValue(CommandParameterProperty),
                    EventArgs=parameter as EventArgs

                };

                if (command != null && command.CanExecute(exParameter)) {
                    /*
                     * ★★★★★★★★★★★★★★★★★★★★★★★★
                     * 注意将扩展的参数传递到Execute方法中
                     * ★★★★★★★★★★★★★★★★★★★★★★★★
                     */
                    command.Execute(exParameter);
                }
            }
        }
        private ICommand ResolveCommand() {
            ICommand result = null;
            if (this.Command != null) {
                result = this.Command;
            } else {
                if (base.AssociatedObject != null) {
                    Type type = base.AssociatedObject.GetType();
                    PropertyInfo[] properties = type.GetProperties(BindingFlags.Instance | BindingFlags.Public);
                    PropertyInfo[] array = properties;
                    for (int i = 0; i < array.Length; i++) {
                        PropertyInfo propertyInfo = array[i];
                        if (typeof(ICommand).IsAssignableFrom(propertyInfo.PropertyType) && string.Equals(propertyInfo.Name, this.CommandName, StringComparison.Ordinal)) {
                            result = (ICommand)propertyInfo.GetValue(base.AssociatedObject, null);
                        }
                    }
                }
            }
            return result;
        }

    }
}

好了，我们把xaml改一下，现在改用我们自己创建的ExInvokeCommandAction

<Window x:Class="EventArgsInViewModel.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
        xmlns:loc="clr-namespace:EventArgsInViewModel"
        Title="MainWindow" Height="350" Width="525">
    <Window.DataContext>
        <loc:MainWindowViewModel />
    </Window.DataContext>
    <Grid>
        <Button Content="Button" Height="38" HorizontalAlignment="Left" Margin="50,52,0,0" Name="button1" VerticalAlignment="Top" Width="138">
            <i:Interaction.Triggers>
                <i:EventTrigger EventName="Click">
                    <!--★★★扩展的InvokeCommandAction★★★-->
                    <loc:ExInvokeCommandAction
                        Command="{Binding ClickCommand}" CommandParameter="{Binding ElementName=button1}" />
                </i:EventTrigger>
            </i:Interaction.Triggers>
        </Button>
    </Grid>
</Window>

ViewModel代码

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Input;
using Microsoft.Practices.Prism.Commands;
using System.Windows;

namespace EventArgsInViewModel {
    public class MainWindowViewModel {
        public ICommand ClickCommand {
            get {
                return new DelegateCommand<ExCommandParameter>((p) => {
                    RoutedEventArgs args = p.EventArgs as RoutedEventArgs;
                    MessageBox.Show(args.ToString());
                },
                (p) => {
                    return true;
                }
                );
            }
        }
    }
}

现在点击一下按钮，显示了对应的消息框，OK，参数也能得到。是不是也很容易啊。
那么有人问，除了ExInvokeCommandAction我也会，但是ExInvokeCommandAction让人想破脑袋也不会写。其实，我也不会写，我只是用ILSpy反编译了一下，然后稍稍改动而已（这个我还是可以做到的）。
最后我想说：“其实你只要动脑筋都做到的事很多！”

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