如何：使用事件属性处理多个事件
若要使用事件属性，请在引发事件的类中定义事件属性，然后在处理事件的类中设置事件属性的委托。 若要在类中实现多个事件属性，此类应该在内部存储和维护为每个事件定义的委托。 对于每字段类事件，会生成相应的支持字段引用类型。 当事件数增加时，这可能会导致不必要的分配。 一种常用的替代方法是维护按密钥存储事件的 EventHandlerList。
若要存储每个事件的委托，则可以使用 EventHandlerList 类，或实现自己的集合。 集合类必须基于事件键提供用于设置、访问和检索事件处理程序委托的方法。 例如，可以使用 Hashtable 类，或从 DictionaryBase 类中派生一个自定义的类。 委托集合的实现细节不需要在你的类的外部公开。
类中的每个事件属性都定义了一个 add 访问器方法和一个 remove 访问器方法。 事件属性的 add 访问器将输入委托实例添加到委托集合。 事件属性的 remove 访问器将输入委托实例从委托集合中移除。 事件属性访问器使用的预定义的事件属性键来将实例添加到委托集合或从中将实例移除。
使用事件属性处理多个事件
定义引发事件的类中的委托集合。
定义每个事件的键。
定义引发事件的类中的事件属性。
使用委托集合实现添加和移除事件属性的 add 和 remove 访问器方法。
使用公共事件属性来添加和移除处理事件的类中的事件处理程序委托。
示例
下面的 C# 示例实现事件属性 MouseDown 和 MouseUp，其中使用 EventHandlerList 来存储每个事件的委托。 事件属性构造的关键字是粗体类型。
// The class SampleControl defines two event properties, MouseUp and MouseDown.
ref class SampleControl : Component
{
// :
// Define other control methods and properties.
// :
// Define the delegate collection.
protected:
EventHandlerList^ listEventDelegates;
private:
// Define a unique key for each event.
static Object^ mouseDownEventKey = gcnew Object();
static Object^ mouseUpEventKey = gcnew Object();
// Define the MouseDown event property.
public:
SampleControl()
{
listEventDelegates = gcnew EventHandlerList();
}
event MouseEventHandler^ MouseDown
{
// Add the input delegate to the collection.
void add(MouseEventHandler^ value)
{
listEventDelegates->AddHandler(mouseDownEventKey, value);
}
// Remove the input delegate from the collection.
void remove(MouseEventHandler^ value)
{
listEventDelegates->RemoveHandler(mouseDownEventKey, value);
}
// Raise the event with the delegate specified by mouseDownEventKey
void raise(Object^ sender, MouseEventArgs^ e)
{
MouseEventHandler^ mouseEventDelegate =
(MouseEventHandler^)listEventDelegates[mouseDownEventKey];
mouseEventDelegate(sender, e);
}
}
// Define the MouseUp event property.
event MouseEventHandler^ MouseUp
{
// Add the input delegate to the collection.
void add(MouseEventHandler^ value)
{
listEventDelegates->AddHandler(mouseUpEventKey, value);
}
// Remove the input delegate from the collection.
void remove(MouseEventHandler^ value)
{
listEventDelegates->RemoveHandler(mouseUpEventKey, value);
}
// Raise the event with the delegate specified by mouseUpEventKey
void raise(Object^ sender, MouseEventArgs^ e)
{
MouseEventHandler^ mouseEventDelegate =
(MouseEventHandler^)listEventDelegates[mouseUpEventKey];
mouseEventDelegate(sender, e);
}
}
};
// The class SampleControl defines two event properties, MouseUp and MouseDown.
class SampleControl : Component
{
// :
// Define other control methods and properties.
// :
// Define the delegate collection.
protected EventHandlerList listEventDelegates = new EventHandlerList();
// Define a unique key for each event.
static readonly object mouseDownEventKey = new object();
static readonly object mouseUpEventKey = new object();
// Define the MouseDown event property.
public event MouseEventHandler MouseDown
{
// Add the input delegate to the collection.
add
{
listEventDelegates.AddHandler(mouseDownEventKey, value);
}
// Remove the input delegate from the collection.
remove
{
listEventDelegates.RemoveHandler(mouseDownEventKey, value);
}
}
// Raise the event with the delegate specified by mouseDownEventKey
private void OnMouseDown(MouseEventArgs e)
{
MouseEventHandler mouseEventDelegate =
(MouseEventHandler)listEventDelegates[mouseDownEventKey];
mouseEventDelegate(this, e);
}
// Define the MouseUp event property.
public event MouseEventHandler MouseUp
{
// Add the input delegate to the collection.
add
{
listEventDelegates.AddHandler(mouseUpEventKey, value);
}
// Remove the input delegate from the collection.
remove
{
listEventDelegates.RemoveHandler(mouseUpEventKey, value);
}
}
// Raise the event with the delegate specified by mouseUpEventKey
private void OnMouseUp(MouseEventArgs e)
{
MouseEventHandler mouseEventDelegate =
(MouseEventHandler)listEventDelegates[mouseUpEventKey];
mouseEventDelegate(this, e);
}
}
' The class SampleControl defines two event properties, MouseUp and MouseDown.
Class SampleControl
Inherits Component
' :
' Define other control methods and properties.
' :
' Define the delegate collection.
Protected listEventDelegates As New EventHandlerList()
' Define a unique key for each event.
Shared ReadOnly mouseDownEventKey As New Object()
Shared ReadOnly mouseUpEventKey As New Object()
' Define the MouseDown event property.
Public Custom Event MouseDown As MouseEventHandler
' Add the input delegate to the collection.
AddHandler(Value As MouseEventHandler)
listEventDelegates.AddHandler(mouseDownEventKey, Value)
End AddHandler
' Remove the input delegate from the collection.
RemoveHandler(Value As MouseEventHandler)
listEventDelegates.RemoveHandler(mouseDownEventKey, Value)
End RemoveHandler
' Raise the event with the delegate specified by mouseDownEventKey
RaiseEvent(sender As Object, e As MouseEventArgs)
Dim mouseEventDelegate As MouseEventHandler = _
listEventDelegates(mouseDownEventKey)
mouseEventDelegate(sender, e)
End RaiseEvent
End Event
' Define the MouseUp event property.
Public Custom Event MouseUp As MouseEventHandler
' Add the input delegate to the collection.
AddHandler(Value As MouseEventHandler)
listEventDelegates.AddHandler(mouseUpEventKey, Value)
End AddHandler
' Remove the input delegate from the collection.
RemoveHandler(Value As MouseEventHandler)
listEventDelegates.RemoveHandler(mouseUpEventKey, Value)
End RemoveHandler
' Raise the event with the delegate specified by mouseDownUpKey
RaiseEvent(sender As Object, e As MouseEventArgs)
Dim mouseEventDelegate As MouseEventHandler = _
listEventDelegates(mouseUpEventKey)
mouseEventDelegate(sender, e)
End RaiseEvent
End Event
End Class
