Developing User Interfaces with Event-driven Programming

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Developing User Interfaces with Event-driven
Programming
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Session Focus

• Improve application performance for UI-intensive
  applications
• Modularize code making it easier to read

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Overview

• What are effective user interfaces
• Developing user interfaces
• LabVIEW Event Structure
• Event programming tips

LabVIEW Event Structure
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Effective User Interfaces

• Display information intuitively and
  professionally
• Descriptive labels on controls
• Limit your VI to 3 standard fonts
• Provides easy control of the user interface
• Enter values
• Change parameters
• Drag-n-drop

NI Style Guide
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Elements of Interactive Interfaces

• Reacting to button clicks
• Entering data and reacting to it
• Drag and drop
• Right-click menus

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Developing Interactive Interfaces with Polling

• While loop checks the value of controls
• Code executes based on the control value
• Drawbacks of polling
• Processor intensive
• Code must process the control value each loop
• Application can appear unresponsive or sluggish
• Can miss user actions
• Reaction of the code is dependent on data flow

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User Interfaces with Polling Demonstration
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UI Development with Event-driven Programming

• Increases application responsiveness
• Easier to read and manager your code

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Event-driven Programming Demonstration
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What is an Event?

• An event is an action that triggers a change in
  state
• User initiated
• button press
• mouse click
• OS initiated
• timeout
• Software initiated
• message from another program
• variable reaches a specific value

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What is an Event Handler?

• Mechanism for communicating with Operating System
• Interprets low-level registry information for
  each event
• Asynchronous callback routine

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The LabVIEW Event Structure
Placed on the Block Diagram like all other
LabVIEW Structures
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Configuring an Event Demonstration
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Parts of an Event Structure
Event Selector Label identifies currently shown
event case
Timeout - value in milliseconds to wait for
eventsdefault value is 1 (indefinite)
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Parts of an Event Structure
Event Filter Node - allows you to change or
discard event data for a Filter event before the
event is completely processed
Event Data Node - data unique to each event case
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Configuring an Event
Right-click
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Event Specifiers
Front Panel Controlsand Indicators
Available Events
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Types of Events
Control
This VI
Application
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Notify and Filter Events

• Notify Events
• Notifies LabVIEW that a user action has already
  occurred available only in the Event Data Node
• Filter Events
• Validates or changes the event data before the
  user interface can process it preventing the
  change from affecting the VI available in the
  Event Filter Node and Event Data Node

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Additional Events

• Right-click Menus
• Registers events based on right-click menu
  activation or selection
• Works with user-defined right-click menus or the
  default application menu
• Drag and Drop
• Drag and drop data between controls and
  indicators
• Useful alternative to copy and paste

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Additional Events Demonstration
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LabVIEW Event Structure Review

• Sleeps until an event occurs
• Executes the appropriate event case
• Does not implicitly loop
• Queues all events
• Executes events in order of occurrence

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Use Templates for the Event Structure

• User Interface Event Handler
• Producer/Consumer (Events)
• State Machine
• Parallel Loop VI Architecture
• Queued Message Handler
• Producer/Consumer (Data)
• Combine or Expand Architectures as Needed

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Event-driven Programming Tips

• Make sure Event Structures are always in loops to
  handle events
• Put Latched Booleans inside of the event case
  handling it
• Programmatic changes DO NOT generate events
• An event-handling loop is not a state machine
• Use a Stop event when in a loop
• Never place an event structure inside of another
  event structure

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Other Resources

• Event Driven Programming in LabVIEW
• LabVIEW Help - Caveats and Recommendations when
  Using Events in LabVIEW
• NI Style Guide
• www.ni.com/info - eventdriven

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Experienced User LabVIEW Intermediate I LabVIEW
Intermediate II
Advanced User LabVIEW Advanced I
Courses
New User LabVIEW Basics I LabVIEW Basics II

• Skills learned
• Modular application development
• Structured design and development practices
• Inter-application communication and connectivity
  techniques

• Skills learned
• LabVIEW environment navigation
• Basics application creation using LabVIEW
• Basics of data acquisition and instrument control

• Skills learned
• Large application design
• Advanced development techniques
• Implementing multideveloper projects

• Certified LabVIEW Architect Exam
• Skills tested
• LabVIEW application development mastery

• Certified LabVIEW Developer Exam
• Skills tested
• LabVIEW application development expertise

• Certifications
• Certified LV Associate Developer Exam
• Skills tested
• LabVIEW environment knowledge

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Connect with the LabVIEW Community
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Questions?Thank You