In order to enable the direct preview or export functionality within the designer, you have to set one or both of the following options:
•LL_OPTION_DESIGNERPREVIEWPARAMETER for preview of real data
•LL_OPTION_DESIGNEREXPORTPARAMETER for the export from the designer
The value that you pass via these options can be defined by yourself, for example a pointer to an internal data structure or object. You receive this back unchanged in the callback (scLlDesignerPrintJob._nUserParam). Important for List & Label is that it is not 0 or -1.
Via callback LL_NTFY_DESIGNERPRINTJOB List & Label informs you about the task that has to be performed. This callback will always be called in the context of the designer thread (this is the thread, from which LlDefineLayout() was called).
When you use structure members, e.g. like _nUserParam, please ensure that the thread has evaluated or copied them before you pass control back to List & Label, as the structure will no longer be valid then – this is true for all Callbacks!