事件聚合IEventAggregator和 Ihandle<T>

-事件聚合IEventAggregator和 Ihandle<T>

 

今天 说一下Caliburn.Micro的IEventAggregator和IHandle<T>分成两篇去讲这一篇写一个简单的例子

看一它的的实现和源码

下一篇用它们做一个多语言的demo

这两个是事件的订阅和广播，很强大，但用的时候要小心发生不必要的冲突。

先看一下它的实现思想

在Caliburn.Micro里EventAggregator要以单例的形式出现这样可以做到对广播做到统一的管理

对象实现IHand<T>接口后通过EventAggregator的subsribe方法把自己加入到Handler集合中这样就能接叫信息

能过EventAggregator.Publish(object obj)方法去发送广播

源码： CaliburnIHandle.rar

先看一下个小demo再去分析它的源码是怎么实现的

效果

      

先写一个消息类，这个类只是做一个IHandle<T>的类型应用没有什么实际意义

    class MyMessage
    {
        public string Str
        {
            get;
            set;
        }
        public override string ToString()
        {
            return Str;
        }
    }

建一个窗体MainView和一个ViewModel类

<Window x:Class="CaliburnIHandle.MyViews.MyMainView"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MyMainView" Height="300" Width="300">
    <StackPanel>
        <TextBox x:Name="StrMessage" Margin="5"/>
        <Button x:Name="OpenOneWin" Content="OpenOneWin" Margin="5"/>       
        <Button Content="Publish" x:Name="Publish" Margin="5"/>
    </StackPanel>
</Window>

窗体有一个textBox显示消息。一个button打开窗体一个发布消息
再看一下ViewModel

实现 了两个IHandle<T> 一个是string 类型一个是我们自己定义的MyMessage

MainViewMode发布string类型的广播也接收string类型和MyMessage类型的消息

 [Export(typeof(IShell))]
    class MyMainViewModel : PropertyChangedBase, IHandle<string>,IHandle<MyMessage>
    {
        readonly IEventAggregator _events;
        readonly IWindowManager _windowManager;
        string strMessage;
        public string StrMessage
        {
            get
            {
                return strMessage;
            }
            set
            {
                strMessage = value;
                NotifyOfPropertyChange(() => StrMessage);
            }
        }
       

        [ImportingConstructor]
        public MyMainViewModel(IEventAggregator e,IWindowManager win)
        {
            _events = e;
            _events.Subscribe(this);
            _windowManager = win;
        }



        public void Handle(string message)
        {
            StrMessage = message;
        }
        public void Handle(MyMessage message)
        {
            StrMessage = message.ToString();
        }

        #region 
        public void Publish()
        {
            _events.Publish(StrMessage);
        }
        #endregion

        #region 打开窗体
        public void OpenOneWin()
        {
            OneCViewModel _one=new OneCViewModel();
            _windowManager.ShowWindow(_one);
        }
        #endregion

再建一个窗体做接收和广播

它只接收string类型的消息和发布MyMessage类型的消息

<UserControl x:Class="CaliburnIHandle.MyViews.OneCView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d" 
             
             Height="300" Width="300">
    <StackPanel>
        <TextBlock FontSize="13" HorizontalAlignment="Center">1</TextBlock>
        <TextBox Margin="5" x:Name="OneMessage"></TextBox>
        <Button Margin="5" x:Name="OnePublish" Content="Publish"/>
    </StackPanel>
</UserControl>

using Caliburn.Micro;
using CaliburnIHandle.CommonC;
using System;
using System.Collections.Generic;
using System.ComponentModel.Composition;
using System.Linq;
using System.Text;

namespace CaliburnIHandle.MyViewModels
{
    [Export(typeof(OneCViewModel))]
    class OneCViewModel : PropertyChangedBase, IHandle<string>
    {
        readonly IEventAggregator _event;
        string oneMessage;
        public string OneMessage
        {
            get
            {
                return oneMessage;
            }
            set
            {
                oneMessage = value;
                NotifyOfPropertyChange(() => OneMessage);
            }
        }
        public OneCViewModel()
        {
            _event = IoC.Get<IEventAggregator>();
            _event.Subscribe(this);
        }


        public void OnePublish()
        {
            _event.Publish(new MyMessage { Str = OneMessage + " One!" });
        }

        public void Handle(string message)
        {
            OneMessage = message;
        }
    }
}

这是一个很简单的例子我们看一下Caliburn.Micro源码它是怎么实现的

看一下IHandle<T>接口

  public interface IHandle<TMessage> : IHandle {  //don't use contravariance here
        /// <summary>
        ///   Handles the message.
        /// </summary>
        /// <param name = "message">The message.</param>
        void Handle(TMessage message);
    }

IHandle<T>只有一个处理T事件的的方法

EventAggregator类通过

 /// <summary>
        ///   Subscribes an instance to all events declared through implementations of <see cref = "IHandle{T}" />
        /// </summary>
        /// <param name = "subscriber">The instance to subscribe for event publication.</param>
        public virtual void Subscribe(object subscriber) {
            if (subscriber == null) {
                throw new ArgumentNullException("subscriber");
            }
            lock(handlers) {
                if (handlers.Any(x => x.Matches(subscriber))) {
                    return;
                }

                handlers.Add(new Handler(subscriber));
            }
        }

把订阅的类放到Handlers集合里

再通过Publish发布相应的消息

       /// <summary>
        ///   Publishes a message.
        /// </summary>
        /// <param name = "message">The message instance.</param>
        /// <remarks>
        ///   Does not marshall the the publication to any special thread by default.
        /// </remarks>
        public virtual void Publish(object message) {
            if (message == null) {
                throw new ArgumentNullException("message");
            }
            Publish(message, PublicationThreadMarshaller);
        }

        /// <summary>
        ///   Publishes a message.
        /// </summary>
        /// <param name = "message">The message instance.</param>
        /// <param name = "marshal">Allows the publisher to provide a custom thread marshaller for the message publication.</param>
        public virtual void Publish(object message, Action<System.Action> marshal) {
            if (message == null){
                throw new ArgumentNullException("message");
            }
            if (marshal == null) {
                throw new ArgumentNullException("marshal");
            }

            Handler[] toNotify;
            lock (handlers) {
                toNotify = handlers.ToArray();
            }

            marshal(() => {
                var messageType = message.GetType();

                var dead = toNotify
                    .Where(handler => !handler.Handle(messageType, message))
                    .ToList();

                if(dead.Any()) {
                    lock(handlers) {
                        dead.Apply(x => handlers.Remove(x));
                    }
                }
            });
        }

作者：李鹏