Chapter 9
Event-Driven Programming
National Instruments recommends you use filter events only when you want to take part in the handling of the user action, either by discarding the event or by modifying the event data. If you only want to know that the user performed a particular action, use notify events. Note
Event structure cases that handle filter events have an Event Filter Node as described in the Event Structure Components section of this chapter. You can change the event data by wiring new values to these terminals. If you do not wire a data item, that item remains unchanged. You can completely discard an event by wiring a TRUE value to the Discard? terminal. A single case in the Event structure cannot handle both notify and filter events. A case can handle multiple notify events but can handle multiple filter events only if the event data items are identical for all events.
Note
Using Events in LabVIEW LabVIEW can generate many different events. To avoid generating unwanted events, use event registration to specify which events you want LabVIEW to notify you about. LabVIEW supports two models for event registration—static and dynamic. Static registration allows you to specify which events on the front panel of a VI you want to handle in each Event structure case on the block diagram of that VI. LabVIEW registers these events automatically when the VI runs. Each event is associated with a control on the front panel of the VI, the front panel window of the VI as a whole, or the LabVIEW application. You cannot statically configure an Event structure to handle events for the front panel of a different VI. Configuration is static because you cannot change at run time which events the Event structure handles. Refer to the Static Event Registration section of this chapter for more information about using static registration. Dynamic event registration avoids the limitations of static registration by integrating event registration with the VI Server, which allows you to use Application, VI, and Control references to specify at run time the objects for which you want to generate events. Dynamic registration provides more flexibility in controlling what events LabVIEW generates and when it generates them. However, dynamic registration is more complex than static registration because it requires using VI Server references with block diagram functions to explicitly register and unregister for events rather than handling registration automatically using the information you configured in the Event structure. Refer to the Dynamic Event Registration section of this chapter for more information about using dynamic registration.
Š National Instruments Corporation
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LabVIEW User Manual