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VECTOREVENTPROC

Summary

Processes each event that occurs inside the vector handle.

Syntax

#include "ltvkrn.h"

L_INT pEXT_CALLBACK YourFunction (pVector, uLevel, pEvent, pUserData)

Parameters

pVECTORHANDLE pVector

Pointer to the vector handle in which the event occurred.

L_UINT uLevel

Level of the event that occurred. For a top-level event, this value is 0. For a second level event this value is 1, etc. For an example, refer to the Comments section below.

pVECTOREVENT pEvent

Pointer to a VECTOREVENT structure that describes the event that occurred in the vector handle.

L_VOID * pUserData

A void pointer that you can use to access a variable or structure containing data that your callback function needs. This gives you a way to receive data indirectly from the function that uses this callback function. (This is the same pointer that you passed in L_VecSetEventCallback.)

Keep in mind that this is a void pointer, which must be cast to the appropriate data type within your callback function.

Returns

The return value is valid only when pEvent->Status is EVENT_STATUS_BEFORE.

Value	Meaning
SUCCESS	Continue with the operation.
SUCCESS_ABORT	Abort this operation only.
< 1	An error occurred. Refer to Return Codes.

Comments

To understand event levels, consider this example:

Assume the clipboard contains a vector handle with 1 layer and 2 objects inside this layer.

Now you execute L_VecCopyFromClipboard, the toolkit may fire these events in the following sequence:

pEvent->uType	pEvent->Status	uLevel	Comment
VECTOR_EVENT_COPYFROMCLIPBOARD	VECTOR_EVENT_BEFORE	0	L_VecCopyFromClipboard is about to execute.
VECTOR_EVENT_ADDLAYER	VECTOR_EVENT_BEFORE	1	L_VecAddLayer is about to execute.
VECTOR_EVENT_ADDOBJECT	VECTOR_EVENT_BEFORE	2	L_VecAddObject for first object is about to execute.
VECTOR_EVENT_ADDOBJECT	VECTOR_EVENT_AFTER	2	L_VecAddObject for first object has been completed.
VECTOR_EVENT_ADDOBJECT	VECTOR_EVENT_BEFORE	2	L_VecAddObject for second object is about to execute.
VECTOR_EVENT_ADDOBJECT	VECTOR_EVENT_AFTER	2	L_VecAddObject for second object has been completed.
VECTOR_EVENT_ADDLAYER	VECTOR_EVENT_AFTER	1	L_VecAddLayer has been completed.
VECTOR_EVENT_COPYFROMCLIPBOARD	VECTOR_EVENT_AFTER	0	L_VecCoptFromClipboard has been completed.

Your callback can monitor all these operations and cancel whatever operation you want.

Returning SUCCESS_ABORT will abort a single operation. For example, to delete objects and not the layers of a vector when L_VecEmpty is called, the callback can be written like this:

L_INT VectorEventCallback( pVECTOREVENT pEvent ) 
{ 
   switch( pEvent->uType ) 
   { 
      case VECTOR_EVENT_DELETEOBJECT: 
      if( pEvent->Status == VECTOR_EVENT_STATUS_BEFORE ) // a chance to cancel 
      { 
         return SUCCESS_ABORT; // cancel this operation only, continue with the rest 
      } 
      break; 
default: 
      break; 
   } 
   return SUCCESS; 
}