Solution
While the front panel appears to be frozen or disabled, it is possible that the event registered in the event structure queue has not finished executing. To check this, right-click the event structure and open the
Event Inspector Window to see if there are multiple events loaded into the event queue. Figure 1 below demonstrates that the "stop 47.2" boolean was clicked 9 times, causing multiple events to be triggered and loaded into the queue. As a result, the user interface will be locked until all events have been handled.
Figure 1. Event Inspect Window - Multiple Boolean Click Example
Some common scenarios that cause the event structure queue to fill up quickly can be found below:
- Rapidly clicking a control that is also registered as a "value change" event.
- Multiple event structures in a while loop and mistakenly assigning multiple identical events for a front panel control. Even if the second structure is not entered until later, the queued event will be triggered upon its occurrence. This is highlighted in the Caveats and Recommendations when Using Events in LabVIEW help documentation in further detail.
- Implementing the event structure in a state machine architecture while not regularly returning to the "Waiting" state for the event structure to process the user inputs.
While these solutions may work, a better solution for programs with time intensive processes is to implement the project using a
Producer/Consumer architecture.