Caliburn.Micro学习笔记(三)----事件聚合IEventAggregator和 Ihandle<T>

Caliburn.Micro学习笔记目录

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));
}
}
});
}