Messenger在MVVM模式中的应用
Messenger在MVVM中应用的前提
我们知道在MVVM架构中，系统平台的Silverlight客户端界面开发和业务逻辑已经被分开，XAML是SL的主要部分，界面设计者只需要绑定ViewModel里的数据即可。但是在ViewModel里有些时候是需要界面发出响应的，在这种情况下，Messenger显示出它的用处。
Messenger的架构
Messager构件代码
定义Imessager接口
注册一个接收消息的类型，比如某一控件来接收消息
void Register<TMessage>(object recipient, Action<TMessage> action);
给最近注册的类型发送消息
void Send<TMessage, TTarget>(TMessage message);
取消最近注册的类型，当执行该句后，不再接收任何消息
void Unregister(object recipient);
实现Imessager接口
public class Messenger : IMessenger
{
private static Messenger _defaultInstance;
private Dictionary<Type, List<WeakActionAndToken>> _recipientsOfSubclassesAction;
private Dictionary<Type, List<WeakActionAndToken>> _recipientsStrictAction;
public static Messenger Default
{
get
{
if (_defaultInstance == null)
{
_defaultInstance = new Messenger();
}
return _defaultInstance;
}
}
public static void OverrideDefault(Messenger newMessenger)
{
_defaultInstance = newMessenger;
}
public static void Reset()
{
_defaultInstance = null;
}
public virtual void Register<TMessage>(object recipient, Action<TMessage> action)
{
Register(recipient, null, false, action);
}
public virtual void Register<TMessage>(object recipient, bool receiveDerivedMessagesToo, Action<TMessage> action)
{
Register(recipient, null, receiveDerivedMessagesToo, action);
}
public virtual void Register<TMessage>(object recipient, object token, Action<TMessage> action)
{
Register(recipient, token, false, action);
}
public virtual void Register<TMessage>(
object recipient,
object token,
bool receiveDerivedMessagesToo,
Action<TMessage> action)
{
var messageType = typeof(TMessage);
Dictionary<Type, List<WeakActionAndToken>> recipients;
if (receiveDerivedMessagesToo)
{
if (_recipientsOfSubclassesAction == null)
{
_recipientsOfSubclassesAction = new Dictionary<Type, List<WeakActionAndToken>>();
}
recipients = _recipientsOfSubclassesAction;
}
else
{
if (_recipientsStrictAction == null)
{
_recipientsStrictAction = new Dictionary<Type, List<WeakActionAndToken>>();
}
recipients = _recipientsStrictAction;
}
List<WeakActionAndToken> list;
if (!recipients.ContainsKey(messageType))
{
list = new List<WeakActionAndToken>();
recipients.Add(messageType, list);
}
else
{
list = recipients[messageType];
}
var weakAction = new WeakAction<TMessage>(recipient, action);
var item = new WeakActionAndToken
{
Action = weakAction,
Token = token
};
list.Add(item);
Cleanup();
}
public virtual void Send<TMessage>(TMessage message)
{
SendToTargetOrType(message, null, null);
}
[SuppressMessage(
"Microsoft.Design",
"CA1004:GenericMethodsShouldProvideTypeParameter",
Justification = "This syntax is more convenient than other alternatives.")]
public virtual void Send<TMessage, TTarget>(TMessage message)
{
SendToTargetOrType(message, typeof(TTarget), null);
}
public virtual void Send<TMessage>(TMessage message, object token)
{
SendToTargetOrType(message, null, token);
}
/// <summary>
public virtual void Unregister(object recipient)
{
UnregisterFromLists(recipient, _recipientsOfSubclassesAction);
UnregisterFromLists(recipient, _recipientsStrictAction);
}
[SuppressMessage(
"Microsoft.Design",
"CA1004:GenericMethodsShouldProvideTypeParameter",
Justification =
"The type parameter TMessage identifies the message type that the recipient wants to unregister for.")]
public virtual void Unregister<TMessage>(object recipient)
{
Unregister<TMessage>(recipient, null);
}
public virtual void Unregister<TMessage>(object recipient, Action<TMessage> action)
{
UnregisterFromLists(recipient, action, _recipientsStrictAction);
UnregisterFromLists(recipient, action, _recipientsOfSubclassesAction);
Cleanup();
}
private static void CleanupList(IDictionary<Type, List<WeakActionAndToken>> lists)
{
if (lists == null)
{
return;
}
var listsToRemove = new List<Type>();
foreach (var list in lists)
{
var recipientsToRemove = new List<WeakActionAndToken>();
foreach (var item in list.Value)
{
if (item.Action == null
|| !item.Action.IsAlive)
{
recipientsToRemove.Add(item);
}
}
foreach (var recipient in recipientsToRemove)
{
list.Value.Remove(recipient);
}
if (list.Value.Count == 0)
{
listsToRemove.Add(list.Key);
}
}
foreach (var key in listsToRemove)
{
lists.Remove(key);
}
}
private static bool Implements(Type instanceType, Type interfaceType)
{
if (interfaceType == null
|| instanceType == null)
{
return false;
}
var interfaces = instanceType.GetInterfaces();
foreach (var currentInterface in interfaces)
{
if (currentInterface == interfaceType)
{
return true;
}
}
return false;
}
private static void SendToList<TMessage>(
TMessage message,
IEnumerable<WeakActionAndToken> list,
Type messageTargetType,
object token)
{
if (list != null)
{
var listClone = list.Take(list.Count()).ToList();
foreach (var item in listClone)
{
var executeAction = item.Action as IExecuteWithObject;
if (executeAction != null
&& item.Action.IsAlive
&& item.Action.Target != null
&& (messageTargetType == null
|| item.Action.Target.GetType() == messageTargetType
|| Implements(item.Action.Target.GetType(), messageTargetType))
&& ((item.Token == null && token == null)
|| item.Token != null && item.Token.Equals(token)))
{
executeAction.ExecuteWithObject(message);
}
}
}
}
private static void UnregisterFromLists(object recipient, Dictionary<Type, List<WeakActionAndToken>> lists)
{
if (recipient == null
|| lists == null
|| lists.Count == 0)
{
return;
}
lock (lists)
{
foreach (var messageType in lists.Keys)
{
foreach (var item in lists[messageType])
{
var weakAction = item.Action;
if (weakAction != null
&& recipient == weakAction.Target)
{
weakAction.MarkForDeletion();
}
}
}
}
}
private static void UnregisterFromLists<TMessage>(
object recipient,
Action<TMessage> action,
Dictionary<Type, List<WeakActionAndToken>> lists)
{
var messageType = typeof(TMessage);
if (recipient == null
|| lists == null
|| lists.Count == 0
|| !lists.ContainsKey(messageType))
{
return;
}
lock (lists)
{
foreach (var item in lists[messageType])
{
var weakActionCasted = item.Action as WeakAction<TMessage>;
if (weakActionCasted != null
&& recipient == weakActionCasted.Target
&& (action == null
|| action == weakActionCasted.Action))
{
item.Action.MarkForDeletion();
}
}
}
}
private void Cleanup()
{
CleanupList(_recipientsOfSubclassesAction);
CleanupList(_recipientsStrictAction);
}
private void SendToTargetOrType<TMessage>(TMessage message, Type messageTargetType, object token)
{
var messageType = typeof(TMessage);
if (_recipientsOfSubclassesAction != null)
{
var listClone = _recipientsOfSubclassesAction.Keys.Take(_recipientsOfSubclassesAction.Count()).ToList();
foreach (var type in listClone)
{
List<WeakActionAndToken> list = null;
if (messageType == type
|| messageType.IsSubclassOf(type)
|| Implements(messageType, type))
{
list = _recipientsOfSubclassesAction[type];
}
SendToList(message, list, messageTargetType, token);
}
}
if (_recipientsStrictAction != null)
{
if (_recipientsStrictAction.ContainsKey(messageType))
{
var list = _recipientsStrictAction[messageType];
SendToList(message, list, messageTargetType, token);
}
}
Cleanup();
}
private struct WeakActionAndToken
{
public WeakAction Action;
public object Token;
}
}
Messager在MVVM的实例
在ViewModel端
public void UpdateJob(object sender, RoutedEventArgs v)
{
var focusrow = (JobMVVMClient.JobBL.View_T_SegmentJob)SelectRow;
if (focusrow != null)
{
JobMVVMClient.JobBL.JobBLClient Job = new JobMVVMClient.JobBL.JobBLClient();
var row = (JobMVVMClient.JobBL.View_T_SegmentJob)selectRow;
if (row.班次号 == null || row.班组号 == null
|| row.计划结束时间 == null || row.计划开始时间 == null || row.投产量 == 0.0)
return;
Job.UpdateSegmentJobBySomeThingCompleted += (s, e) =>
{
if (e.Result)
{
MessageBox.Show(PromptString.UpdateJobYes);
foreach (var element in jobModel.Gradeinfo)
{
if (element.DetailID == row.班次号.ToString())
row.班次 = element.DetailName;
}
foreach (var element in jobModel.Groupinfo)
{
if (element.DetailID == row.班组号.ToString())
row.班组 = element.DetailName;
}
}
};
Messenger.Default.Send<bool?,JobMVVMClinet.Views.JobPlanUpdateView>(true);
//给位于View层中的JobPlanUpdateView这个界面发送bool消息,这个消息是true.
Job.UpdateSegmentJobBySomeThingAsync(row.工单ID, row.投产量, (DateTime)row.计划开始时间, (DateTime)row.计划结束时间, (int)row.班次号, (int)row.班组号);
Job.CloseAsync();
}
}
在VIEW端
public partial class JobPlanUpdateView : ChildWindow
{
public JobPlanUpdateView(CreateJobViewModel model)
{
InitializeComponent();
DataContext = model;
Messenger.Default.Register<bool?>(this, m => this.DialogResult = m);
//注册接收消息，并且做出响应处理
}
}
Messager总结
消息在MVVM中广泛应用，更好的运用MESSAGER能更好的处理View与ViewModel的关系，为MVVM添加喝彩。