CLAD CLAD User Interface & Event Handling 1 — Questions and Answers
Question 1: What is the primary purpose of the Event Structure in LabVIEW?
- To handle file I/O events
- To respond to user interface interactions and programmatic events without polling (Correct answer)
- To create timed loops
- To manage hardware interrupts
Correct 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.
Question 2: Which type of event in LabVIEW is generated before the control value changes and can be discarded?
- Value Change event
- Mouse Down event
- Filter event (Correct answer)
- Notify event
Correct 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.
Question 3: How do you prevent a LabVIEW front panel control from being modified by the user while the VI is running?
- Set the control to indicator type
- Right-click the control and select 'Key Navigation > Tab Stop: Off'
- Change the control's mechanical action to 'Latch When Pressed'
- Use the 'Disable' property node to set the control's disabled state (Correct answer)
Correct 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.
Question 4: What is the difference between a Control and an Indicator on a LabVIEW front panel?
- Controls are only numeric; indicators are only Boolean
- Controls accept user input and provide data to the block diagram; indicators display output data (Correct answer)
- Controls run faster than indicators
- There is no functional difference
Correct 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.
Question 5: Which LabVIEW structure is commonly used together with an Event Structure to build a responsive GUI application?
- Sequence Structure
- While Loop (Correct answer)
- For Loop
- Case Structure
Correct 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.
Question 6: What does the 'Lock Front Panel' option in an Event Structure do?
- Prevents the user from resizing the front panel
- Blocks other events from being processed while the current event case is executing (Correct answer)
- Saves the front panel layout
- Locks all controls to their current values
Correct 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.
CLAD CLAD User Interface & Event Handling 1
What is the primary purpose of the Event Structure in LabVIEW?