CLAD User Interface & Event Handling Flashcards

What is the primary purpose of the Event Structure in LabVIEW?

Answer: To respond to user interface interactions and programmatic events without polling

The Event Structure waits for registered events (such as button clicks or value changes) and executes the appropriate case, eliminating the need for constant polling.

Which type of event in LabVIEW is generated before the control value changes and can be discarded?

Answer: Filter event

Filter events (indicated by a '?' suffix) occur before the action is committed, allowing the program to modify or discard the event before it affects the control.

How do you prevent a LabVIEW front panel control from being modified by the user while the VI is running?

Answer: Use the 'Disable' property node to set the control's disabled state

Setting a control's Disabled property to Disabled+Grayed Out via a property node prevents user interaction while visually indicating the control is unavailable.

What is the difference between a Control and an Indicator on a LabVIEW front panel?

Answer: Controls accept user input and provide data to the block diagram; indicators display output data

Controls are inputs (data sources on the block diagram) that the user or external code sets, while indicators are outputs (data sinks) that display computed results.

Which LabVIEW structure is commonly used together with an Event Structure to build a responsive GUI application?

Answer: While Loop

A While Loop enclosing an Event Structure creates a standard GUI pattern that continuously waits for events and processes them until a stop condition is met.

What does the 'Lock Front Panel' option in an Event Structure do?

Answer: Blocks other events from being processed while the current event case is executing

When Lock Front Panel is enabled, LabVIEW prevents new user interactions from being queued while the current event case is still executing, avoiding re-entrant GUI issues.