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IVisEventProc.VisEventProc method (Visio)

  • Artikkeli

Private member function of IVisEventProc that handles event notifications passed to it by the EventList.AddAdvise method.

Syntax

expression.VisEventProc (nEventCode, pSourceObj, nEventID, nEventSeqNum, pSubjectObj, vMoreInfo)

expression A variable that represents an IVisEventProc object.

Parameters

Name Required/Optional Data type Description
nEventCode Required Integer The event or events that occurred.
pSourceObj Required Object The object whose EventList collection contains the Event object that sent the notification.
nEventID Required Long The unique identifier of the Event object within the EventList collection.
nEventSeqNum Required Long The ordinal position of the event with respect to the sequence of events that have occurred in the calling instance of the application.
pSubjectObj Required Object The subject of the event, which is the object to which the event occurred. See Remarks for examples.
vMoreInfo Required Variant Additional information about the subject of the event. See Remarks for more information.

Return value

Variant

Remarks

To handle event notifications, create a class module that implements the IVisEventProc interface and then create an instance of this class to pass as an argument to the AddAdvise method of the EventList collection. Use the AddAdvise method to create Event objects that send the notifications.

The nEventCode parameter identifies the specific event or events that occurred. The EventCode argument of the AddAdvise method is passed to VisEventProc as nEventCode. Within your procedure, you can use any branching technique you want to determine which event occurred and handle it. The example that accompanies this topic uses a Select Case decision structure.

Unlike the Index property of the EventList collection, nEventID does not change as Event objects are added or deleted from the collection.

From within VisEventProc, you can use the following code to get the Event object that sent the notification.

pSourceObj. EventList.ItemFromID(nEventID )

The connection between the source object pSourceObj and the Event object exists until one of the following occurs:

  • The program deletes the Event object.

  • The program releases the last reference to the source object. (The EventList collection and Event objects hold a reference to their source object.)

  • The Microsoft Visio application instance terminates.

The first event that occurs in a Visio instance has nEventSeqNum = 1, the second event = 2, and so on. In some cases, you can use the sequence number in conjunction with the EventInfo property to obtain more information about the event.

The pSubjectObj parameter for a ShapeAdded event is a Shape object that represents the shape that was just added, while the subject of a BeforeSelectionDelete event is a Selection object in which the shapes that are about to be deleted are selected.

For many events, vMoreInfo is a string similar to the command line the application passes to the add-ons it executes. If the notification does not include additional information, this parameter is set to Nothing. For details about notification parameters for a particular event, see the particular event topic in this reference.

Beginning with Visio 2000, VisEventProc is defined as a function that returns a value. However, Visio only looks at return values from calls to VisEventProc that are passed a query event code. Sink objects that provide VisEventProc through IDispatch require no change. To modify existing event handlers so that they can handle query events, change the Sub procedure to a Function procedure and return the appropriate value. (For details about query events, see this reference for event topics prefixed with Query.)

If nEventCode identifies a query event (events prefixed with Query), return True from VisEventProc to cancel the event, and return False to allow it to happen. The value is arbitrary for other events. If you don't return an explicit value, Microsoft Visual Basic for Applications (VBA) returns an empty Variant, which Visio interprets as False.

Example

This example shows how to create a class module that implements IVisEventProc to handle events fired by a source object in Visio, for example, the Document object. The module consists of the function VisEventProc, which uses a Select Case block to check for three events: DocumentSaved, PageAdded, and ShapesDeleted. Other events fall under the default case (Case Else). Each Case block constructs a string (strMessage) that contains the name and event code of the event that fired. Finally, the function displays the string in the Immediate window.

Copy this sample code into a new class module in VBA or Visual Basic, naming the module clsEventSink. You can then use an event-sink module to create an instance of the clsEventSink class and Event objects that send notifications of event firings to the class instance. To see how to create an event-sink module, see the example for the AddAdvise method.

 
Implements Visio.IVisEventProc 
 
 
'Declare visEvtAdd as a 2-byte value 
'to avoid a run-time overflow error 
Private Const visEvtAdd% = &H8000 
 
Private Function IVisEventProc_VisEventProc( _ 
 ByVal nEventCode As Integer, _ 
 ByVal pSourceObj As Object, _ 
 ByVal nEventID As Long, _ 
 ByVal nEventSeqNum As Long, _ 
 ByVal pSubjectObj As Object, _ 
 ByVal vMoreInfo As Variant) As Variant 
 
 Dim strMessage As String 
 
 
 'Find out which event fired 
 Select Case nEventCode 
 Case visEvtCodeDocSave 
 strMessage = "DocumentSaved (" & nEventCode & ")" 
 Case (visEvtPage + visEvtAdd) 
 strMessage = "PageAdded (" & nEventCode & ")" 
 Case visEvtCodeShapeDelete 
 strMessage = "ShapesDeleted(" & nEventCode & ")" 
 Case Else 
 strMessage = "Other (" & nEventCode & ")" 
 End Select 
 
 
 'Display the event name and the event code 
 Debug.Print strMessage 
 
End Function

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