如何：使用事件属性处理多个事件

项目
08/12/2011

要使用事件属性（Visual Basic 2005 中的自定义事件），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。要在一个类中实现多个事件属性，该类必须在内部存储和维护为每个事件定义的委托。一种典型方法是实现通过事件键进行索引的委托集合。

若要存储每个事件的委托，可以使用 EventHandlerList 类或实现您自己的集合。集合类必须提供用于基于事件键设置、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 类派生一个自定义类。不需要在类以外公开委托集合的实现详细信息。

类中的每个事件属性定义一个 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 访问器从委托集合中移除输入委托实例。事件属性访问器使用事件属性的预定义键在委托集合中添加和从委托集合中移除实例。

使用事件属性处理多个事件

在引发事件的类中定义一个委托集合。
定义每个事件的键。
在引发事件的类中定义事件属性。
使用委托集合实现事件属性的 add 访问器方法和 remove 访问器方法。
使用公共事件属性可在处理事件的类中添加和移除事件处理程序委托。

示例

下面的 C# 示例使用 EventHandlerList 存储每个事件的委托，从此来实现事件属性 MouseDown 和 MouseUp。事件属性构造的关键字用粗体表示。

注意
Visual Basic 2005 中不支持事件属性。

' 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

// 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.
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);
        }
    }
};

请参见

通过

如何：使用事件属性处理多个事件

使用事件属性处理多个事件

示例

请参见

任务

参考

概念

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