如何：使用事件屬性處理多個事件

發行項
05/22/2023

為了要使用事件屬性，您會在引發事件的類別中定義事件屬性，然後在處理事件的類別中設定事件屬性的委派。若要在類別中實作多個事件屬性，該類別內部必須儲存及維護為每個事件所定義的委派。針對每個類似欄位的事件，會產生對應的支援欄位參考型別。當事件數目增加時，這可能會導致不必要的配置。或者，常見的方法是維護依索引鍵儲存事件的 EventHandlerList。

若要儲存每個事件的委派，您可以使用 EventHandlerList 類別，或實作您自己的集合。集合類別必須提供方法，根據事件索引鍵來設定、存取和擷取事件處理常式委派。例如，您可以使用 Hashtable 類別，或是從 DictionaryBase 類別衍生自訂類別。委派集合的實作詳細資料不需要公開至類別之外。

類別內的每個事件屬性，都會定義一個 add 存取子方法和一個 remove 存取子方法。事件屬性的 add 存取子會在委派集合中加入輸入委派執行個體。事件屬性的 remove 存取子會從委派集合中移除輸入委派執行個體。事件屬性存取子會使用事件屬性的預先定義索引鍵，從委派集合新增和移除執行個體。

使用事件屬性處理多個事件

定義在類別中引發事件的委派集合。
定義每個事件的索引鍵。
在引發事件的類別中定義事件屬性。
使用委派集合實作事件屬性的 add 和 remove 存取子方法。
使用公用事件屬性，在處理事件的類別中新增和移除事件處理常式委派。

範例

下列 C# 範例會使用 EventHandlerList 實作事件屬性 MouseDown 及 MouseUp，以儲存每個事件的委派。事件屬性建構的關鍵字會以粗體顯示。

// 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

如何：使用事件屬性處理多個事件

使用事件屬性處理多個事件

範例

另請參閱

意見反應

其他資源