关于WPF中Command绑定传参数以及将命令绑定到其它事件的方法

前言：在WPF中，将命令绑定到一个Button的Command属性中是非常简单的事情，例如：

<Button Content="单击命令" Command="{Binding ClickCommand}"/>

但是很多时候，我们要实现其它事件的命令绑定，以此实现彻底的MVVM开发模式，那就得用到微软另外一个神器了！它就是程序集System.Windows.Interactivity，在网上可以下载System.Windows.Interactivity.dll这个库文件。

当然，在mvvmlight中，已经集成了这个库文件，所以我们新建一个WPF项目后，通过“管理Nuget程序包"下载安装mvvmlight到项目中后，就可以直接使用了，mvvmlight组件是WPF常见开发包，它提供了一个GalaSoft.MvvmLight.Command命令空间，其中有RelayCommand和RelayCommand<T>两个类扩展了ICommand接口，特别是RelayCommand<T>类，它能实现参数传递。

比如我们有一个ComboBox控件，当用户在UI端选定某个子项后，要将选定的值传入到ViewModel中，这里就需要将ComboBox的SelectionChanged事件绑定到一个命令（SelectionComboBoxCommand），绑定的同时可将当前这个ComboBox控件作为参数传递给SelectionComboBoxCommand命令，这样就可以在ViewModel中去作处理了，那么具体的操作怎么实现呢？

首先是前端代码：

<ComboBox>
  <i:Interaction.Triggers>
      <i:EventTrigger EventName="SelectionChanged">
          <i:InvokeCommandAction Command="{Binding SelectionComboBoxCommand}" CommandParameter="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=ComboBox}}"/>
      </i:EventTrigger>
  </i:Interaction.Triggers>
  <ComboBoxItem Content="张三"/>
  <ComboBoxItem Content="李四"/>
  <ComboBoxItem Content="王五"/>
</ComboBox>

这里就使用了System.Windows.Interactivity这个空间的Interaction.Triggers，将ComboBox的SelectionChanged事件传递到SelectionComboBoxCommand命令中，在后端，SelectionComboBoxCommand定义成泛型，接收前端传入的ComboBox控件

/// <summary>
/// 获取ComboBox的选定项
/// </summary>
public RelayCommand<ComboBox> SelectionComboBoxCommand
{
    get
    {
        var command = new RelayCommand<ComboBox>((control) =>
        {
            var item = control.SelectedItem as ComboBoxItem;
            if (item != null)
                messages.Add($"({item.Content})[{DateTime.Now}]");
        });
        return command;
    }
}

如此，就可以拿到ComboBox的SelectedItem ，并进行相应的处理了。本例中还展示了Microsoft.Practices.Prism空间中的DelegateCommand类的用法，和mvvmlight中的RelayCommand一样

/// <summary>
/// 获取ComboBox的选定项
/// </summary>
public DelegateCommand<ComboBox> SelectionComboBoxCommand2
{
    get
    {
        var command = new DelegateCommand<ComboBox>((control) =>
        {
            var item = control.SelectedItem as ComboBoxItem;
            if (item != null)
                messages.Add($"({item.Content})[{DateTime.Now}]");
        });
        return command;
    }
}

完整的代码如下：

前端代码

<Window x:Class="WpfCommands.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfCommands" xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
        mc:Ignorable="d" DataContext="{Binding Source={StaticResource Locator},Path=Main}"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition/>
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>
        <StackPanel>
            <Button Content="单击命令" Command="{Binding ClickCommand}"/>
            <Button Content="单击命令带参数" Command="{Binding ClickWithButtonCommand}"  CommandParameter="{Binding RelativeSource={RelativeSource Mode=Self}}"/>
            <TextBox>
                <i:Interaction.Triggers>
                    <i:EventTrigger EventName="GotFocus">
                        <i:InvokeCommandAction Command="{Binding GotFocusWithTextBoxCommand }" CommandParameter="{Binding RelativeSource={RelativeSource Mode=FindAncestor,AncestorType=TextBox}}"/>
                    </i:EventTrigger>
                    <i:EventTrigger EventName="TextChanged">
                        <i:InvokeCommandAction Command="{Binding ChangedTextBoxCommand}" CommandParameter="{Binding RelativeSource={RelativeSource Mode=FindAncestor,AncestorType=TextBox}}"/>
                    </i:EventTrigger>
                </i:Interaction.Triggers>
            </TextBox>
            <ComboBox>
                <i:Interaction.Triggers>
                    <i:EventTrigger EventName="SelectionChanged">
                        <i:InvokeCommandAction Command="{Binding SelectionComboBoxCommand}" CommandParameter="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=ComboBox}}"/>
                    </i:EventTrigger>
                </i:Interaction.Triggers>
                <ComboBoxItem Content="张三"/>
                <ComboBoxItem Content="李四"/>
                <ComboBoxItem Content="王五"/>
            </ComboBox>
        </StackPanel>
        <ListBox Grid.Column="1" ItemsSource="{Binding Messages}"/>
    </Grid>
</Window>

ViewModel代码

using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.Command;
using Microsoft.Practices.Prism.Commands;
using System;
using System.Collections.ObjectModel;
using System.Windows.Controls;

namespace WpfCommands.ViewModel
{
    public class MainViewModel : ViewModelBase
    {
        public MainViewModel()
        {

        }

        private ObservableCollection<string> messages = new ObservableCollection<string>();
        /// <summary>
        /// 运行提示
        /// </summary>
        public ObservableCollection<string> Messages
        {
            get { return messages; }
            set { messages = value; RaisePropertyChanged("Messages"); }
        }

        /// <summary>
        /// 单击命令
        /// </summary>
        public RelayCommand ClickCommand
        {
            get
            {
                var command = new RelayCommand(() =>
                {
                    messages.Add($"您单击了[{DateTime.Now}]");
                });
                return command;
            }
        }

        /// <summary>
        /// 单击命令带参数
        /// </summary>
        public RelayCommand<Button> ClickWithButtonCommand
        {
            get
            {
                var command = new RelayCommand<Button>((button) =>
                {
                    messages.Add($"您单击了({button.Content})[{DateTime.Now}]");
                });
                return command;
            }
        }

        /// <summary>
        /// TextBox获得焦点
        /// </summary>
        public RelayCommand<TextBox> GotFocusWithTextBoxCommand
        {
            get
            {
                var command = new RelayCommand<TextBox>((textbox) =>
                {
                    messages.Add($"({textbox.Name})获得焦点[{DateTime.Now}]");
                });
                return command;
            }
        }

        /// <summary>
        /// TextBox内容被修改
        /// </summary>
        public RelayCommand<TextBox> ChangedTextBoxCommand
        {
            get
            {
                var command = new RelayCommand<TextBox>((textbox) =>
                {
                    messages.Add($"({textbox.Text})[{DateTime.Now}]");
                });
                return command;
            }
        }

        /// <summary>
        /// 获取ComboBox的选定项
        /// </summary>
        public RelayCommand<ComboBox> SelectionComboBoxCommand
        {
            get
            {
                var command = new RelayCommand<ComboBox>((control) =>
                {
                    var item = control.SelectedItem as ComboBoxItem;
                    if (item != null)
                        messages.Add($"({item.Content})[{DateTime.Now}]");
                });
                return command;
            }
        }


        /// <summary>
        /// 获取ComboBox的选定项
        /// </summary>
        public DelegateCommand<ComboBox> SelectionComboBoxCommand2
        {
            get
            {
                var command = new DelegateCommand<ComboBox>((control) =>
                {
                    var item = control.SelectedItem as ComboBoxItem;
                    if (item != null)
                        messages.Add($"({item.Content})[{DateTime.Now}]");
                });
                return command;
            }
        }

    }
}

源码下载

下面为新增自定义控件及控件行为附加示例

附带升级版源码（增加自定义控件中自定义事件的命令绑定和控件行为扩展示例）

作者：WPF中文网文章来源地址https://www.toymoban.com/news/detail-502034.html

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