WPF MVVM进阶系列教程（四、ViewModel通信）

🧭 WPF MVVM入门系列教程

• 一、MVVM模式介绍
• 二、依赖属性
• 三、数据绑定
• 四、ViewModel
• 五、命令和用户输入
• 六、ViewModel案例演示

🍠 WPF MVVM进阶系列教程

• 一、对话框
• 二、数据验证
• 三、使用依赖注入(Dependency Injection)
• 四、ViewModel通信

---

 

方式一、通过依赖注入直接调用ViewModel

在前面的文章中，我们介绍了使用DI容器。

在注入ViewModel时，将它的生命周期配置为单例，这样我们就可以在任意的ViewModel中进行互相调用。

 

这里我们创建一个Send窗口和一个Receive窗口。

Send窗口用于发送消息，Receive窗口用于接收消息。

 

Send.xaml

<Window>
    <Grid>
        <Button HorizontalAlignment="Center" VerticalAlignment="Center" Content="Send" Command="{Binding SendMessageCommand}"></Button>
    </Grid>
</Window>

 

SendViewModel

这里我们将接收的ViewModel直接以参数传入，这样就可以直接操作Receive窗口中的列表。

public class SendViewModel
{
    public RelayCommand SendMessageCommand { get; private set; }

    protected ReceiveViewModel receiveViewModel;

    public SendViewModel(ReceiveViewModel receiveViewModel)
    {
        SendMessageCommand = new RelayCommand(SendMessage);

        this.receiveViewModel = receiveViewModel;
    }

    private void SendMessage()
    {
        DateTimeMessage dateTimeMessage = new DateTimeMessage();
        dateTimeMessage.DatetimeNow = DateTime.Now.ToString();
        receiveViewModel.AddDateTimeMessage(dateTimeMessage);
    }
}

 

Receive.xaml

<Window>
    <Grid>
        <ListBox ItemsSource="{Binding MessageList}"></ListBox>
    </Grid>
</Window>

 

ReceiveViewModel

 public class ReceiveViewModel : INotifyPropertyChanged
 {
     private ObservableCollection<string> messageList = new ObservableCollection<string>();

     public ObservableCollection<string> MessageList
     {
         get
         {
             return messageList;
         }

         set
         {
             messageList = value;
             PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("MessageList"));
         }
     }
     public event PropertyChangedEventHandler PropertyChanged;

     public ReceiveViewModel()
     {
         
     }


     public void AddDateTimeMessage(DateTimeMessage message)
     {
         messageList.Add(message.DatetimeNow);
     }
 }

 

然后我们配置DI容器

App.xaml.cs

public partial class App : Application
{
    public static IUnityContainer Container { get; private set; }

    protected override void OnStartup(StartupEventArgs e)
    {
        base.OnStartup(e);

        Container = new UnityContainer();
        RegisterTypes(Container);

        Receive receive = new Receive();
        receive.Show();
    }

    private void RegisterTypes(IUnityContainer container)
    {
        container.RegisterType<SendViewModel>();
        container.RegisterType<ReceiveViewModel>(new ContainerControlledLifetimeManager());
    }
}

 

最后再通过DI容器获取ViewModel并绑定到DataContext

以Receive窗口为例

Receive.xaml.cs

  public partial class Receive : Window
  {
      public Receive()
      {
          InitializeComponent();

          this.DataContext = App.Container.Resolve<ReceiveViewModel>();
      }
  }

 

 

 

方式二、通过回调

以前我们在使用MVVMLight包时，里面有一个Messenger类，它可以在ViewModel中订阅消息，当在其它位置发送这个消息时，订阅的ViewModel就可以接收到这个消息并进行处理。

MVVMLight示例如下：

ReceiveViewModel(创建订阅)

using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.Messaging;

public class ReceiveViewModel : ViewModelBase
{
    public ReceiverViewModel()
    {
        // 注册消息：指定消息类型、接收者（通常是自身）、处理方法
        Messenger.Default.Register<UserMessage>(this, OnUserMessageReceived);
    }

    // 消息处理方法
    private void OnUserMessageReceived(UserMessage message)
    {
        // 处理接收到的消息数据
        var userId = message.UserId;
        var userName = message.UserName;
    }
}

 

SendViewModel(发送)

using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.Command;
using GalaSoft.MvvmLight.Messaging;

public class SenderViewModel : ViewModelBase
{
    public RelayCommand SendMessageCommand { get; private set; }

    public SenderViewModel()
    {
        SendMessageCommand = new RelayCommand(SendMessage);
    }

    private void SendMessage()
    {
        // 创建消息实例并设置数据
        var message = new UserMessage 
        { 
            UserId = 1001, 
            UserName = "张三" 
        };

        // 发送消息
        Messenger.Default.Send(message);
    }
}

 

它这里内部的原理并不是非常复杂，就是利用回调的机制。

核心步骤如下：

1、创建一个字典类型，以类型名称（消息对象）作为Key，回调列表作为值

2、注册时，根据类型名称，将回调添加到列表中

3、发送时，循环列表判断是否注册了对应类型（消息对象），如果有，调用回调函数。

 

接下来我们自己实现一个简单的Messenger类，重在讲解原理。

public class Messager
{
    private static object obj = new object();
    private static Messager instance;
    private Dictionary<Type, List<GenericAction>> recipientsActions = new Dictionary<Type, List<GenericAction>>();
      
    //单例
    public static Messager Instance
    {
        get
        {
            if (instance == null)
            {
                lock (obj)
                {
                    if (instance == null)
                        instance = new Messager();
                }
            }

            return instance;
        }
    }

    //注册
    public void Register<TMessage>(Action<TMessage> action)
    {
        var messageType = typeof(TMessage);


        List<GenericAction> list;

        if (!recipientsActions.ContainsKey(messageType))
        {
            list = new List<GenericAction>();
            recipientsActions.Add(messageType, list);
        }
        else
        {
            list = recipientsActions[messageType];
        }

        //将回调放到列表中
        list.Add(new GenericAction<TMessage>(action));

    }

    public void Send<TMessage>(TMessage message)
    {
        var messageType = typeof(TMessage);

        List<GenericAction> list = new List<GenericAction>();

        if (recipientsActions.ContainsKey(messageType))
        {
            //获取当前消息对应的回调列表
            list = recipientsActions[messageType];
        }

        //循环回调列表并调用
        foreach (GenericAction<TMessage> action in list)
        {
            action.Invoke(message);
        }
    }
}

 

在ReceiveViewModel进行注册

 public class ReceiveViewModel : INotifyPropertyChanged
 {
     private ObservableCollection<string> messageList = new ObservableCollection<string>();

     public ObservableCollection<string> MessageList
     {
         get
         {
             return messageList;
         }

         set
         {
             messageList = value;
             PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("MessageList"));
         }
     }
     public event PropertyChangedEventHandler PropertyChanged;

     public ReceiveViewModel()
     {
         //注册消息
         Messager.Messager.Instance.Register<DateTimeMessage>(ReceiveDateTimeMessage);
     }

     private void ReceiveDateTimeMessage(DateTimeMessage message)
     {
         messageList.Add(message.DatetimeNow);
     }
 }

 

在SendViewModel中发送消息

public class SendViewModel
{
    public RelayCommand SendMessageCommand { get; private set; }

    public SendViewModel()
    {
        SendMessageCommand = new RelayCommand(SendMessage);
    }

    private void SendMessage()
    {
        DateTimeMessage dateTimeMessage = new DateTimeMessage();
        dateTimeMessage.DatetimeNow = DateTime.Now.ToString();
        //发送消息
        Messager.Messager.Instance.Send<DateTimeMessage>(dateTimeMessage);
    }
}

完整代码可以参考文末链接

 

方式三、使用三方包提供的Messenger

注意：方式二重在了解原理，除非有特殊要求，尽量还是使用软件包提供的Messenger类，功能会更加完整和稳定。

这里我们以CommunityToolkit.MVVM包中的WeakReferenceMessenger类进行演示。

 

使用CommunityToolkit.MVVM包时，可通知的对象一般都会继承自ObservableRecipient类型，

这个类型的内部会注入一个WeakReferenceMessenger对象，所以使用起来就比较方便。

 

ReceiveViewModel

public class ReceiveViewModel : ObservableRecipient
{
    private ObservableCollection<string> messageList = new ObservableCollection<string>();

    public ObservableCollection<string> MessageList
    {
        get
        {
            return messageList;
        }

        set
        {
            SetProperty(ref messageList, value);
        }
    }

    public ReceiveViewModel()
    {
        //注册
        this.Messenger.Register<ReceiveViewModel, DateTimeMessage>(this, OnReceiveDateTimeChangedMessage);
    }

    //接收到消息时的回调函数
    private void OnReceiveDateTimeChangedMessage(ReceiveViewModel recipient, DateTimeMessage message)
    {
        messageList.Add(message.Value.DatetimeNow);
    }
}

 

SendViewModel

public class SendViewModel: ObservableRecipient
{
    public RelayCommand SendMessageCommand { get; private set; }

    public SendViewModel()
    {
        SendMessageCommand = new RelayCommand(SendMessage);
    }

    private void SendMessage()
    {
        //发送消息
        this.Messenger.Send<DateTimeMessage>(new DateTimeMessage(new DateTimeDisplay() { DatetimeNow = DateTime.Now.ToString() }));
    }
}

 

示例代码

https://github.com/zhaotianff/WPF-MVVM-Beginner/tree/main/10_ViewModelCommunication