Mediator类完成Controller对象之间的协调，其定义如下：
public class Mediator
{
MultiDictionary<string, IColleague> internalList
= new MultiDictionary<string, IColleague>();
public void Register(IColleague colleague, IEnumerable<string> messages)
{
foreach (string message in messages)
internalList.AddValue(message, colleague);
}
public void NotifyColleagues(string message, object args)
{
if (internalList.ContainsKey(message))
{
//forward the message to all listeners
foreach (IColleague colleague in internalList[message])
colleague.MessageNotification(message, args);
}
}
}
{
MultiDictionary<string, IColleague> internalList
= new MultiDictionary<string, IColleague>();
public void Register(IColleague colleague, IEnumerable<string> messages)
{
foreach (string message in messages)
internalList.AddValue(message, colleague);
}
public void NotifyColleagues(string message, object args)
{
if (internalList.ContainsKey(message))
{
//forward the message to all listeners
foreach (IColleague colleague in internalList[message])
colleague.MessageNotification(message, args);
}
}
}
Register()方法会将消息与Controller对象的映射注册到内部字典internalList中。而 NotifyColleagues()方法则会遍历整个internalList，然后执行Controller对象（体现为IColleague类型） 的MessageNotification()方法。通过MessageNotification()方法，每个Controller对象根据传输的消息字符 串，做出相应的响应操作。例如在FileSelectorController类中，就是根据Message的值，执行装载文件的业务逻辑：
public override void MessageNotification(string message, object args)
{
switch (message)
{
case Messages.DirectorySelectedChanged:
//load all files for the directory specified
LoadFiles((DirectoryDisplayItem)args);
break;
}
}
{
switch (message)
{
case Messages.DirectorySelectedChanged:
//load all files for the directory specified
LoadFiles((DirectoryDisplayItem)args);
break;
}
}
如果没有引入Mediator模式，由于需要在点击目录时显示当前目录的文件，因此在DirectorySelectorController类的 ItemSelected事件中，必须调用FileSelectorController对象获取文件信息，然后通过对应视图显示这些文件信息。这就导致 了DirectorySelectorController和FileSelectorController之间的依赖。现在，在 DirectorySelectorController的ItemSelected事件中，就可以通过Mediator来实现文件信息的读取与显示：
//event handler for the selecting changed
void ItemSelected(object sender, RoutedEventArgs e)
{
TreeView treeView = (TreeView)e.OriginalSource;
//Send a message that an item is selected and pass the object selected
Mediator.NotifyColleagues(Messages.DirectorySelectedChanged, treeView.SelectedItem);
}
void ItemSelected(object sender, RoutedEventArgs e)
{
TreeView treeView = (TreeView)e.OriginalSource;
//Send a message that an item is selected and pass the object selected
Mediator.NotifyColleagues(Messages.DirectorySelectedChanged, treeView.SelectedItem);
}
