Hands-On:
Introduction to
Object-Oriented
Programming in
LabVIEW
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Hardware Requirements:-
None Required
Software Requirements:-
Object Oriented Programming Hands On
1. Launch LabVIEW from Start>>All Programs>> National
Instruments>> LabVIEW 20XX.
2. On the splash-screen, click on Create Project to create a new project.
3. Navigate to Hands On in the left side of the window, select the LabVIEW category
and double-click the OOP Hands On as shown below.
4. Navigate to LabVIEW and a window will prompt you to configure the new project as shown below. Save it to a folder of your choice.
Exercise 1
Concept – The aim of this exercise is to add a message popup to a base VI to show dynamic dispatch.
1. Open the OOP Hands On Project in the Exercises folder.
2. Expand the Classes virtual folder and then the Message Child Classes virtual folder. 3. Right click on the Message Child Classes virtual folder and select New>>Class 4. Change the name to Popup
5. Click OK
6. Double Click the Popup.ctl to open it. Drop a String control into the Cluster of Private Class Data. Re-label this to “Message String”.
7. Close the Popup.ctl and click save. Save the Popup.lvclass file in the exercise1 folder
8. Right click Popup.lvclass in your project and select Properties
9. Then select Inheritance, and click the button Change Inheritance
10. Select Message.lvclass, and click Inherit From Selected and then click OK
11. Now we must create the Accessor Methods for the data in the class.
12. Right click Popup.lvclass and select New>>VI for Data Member Access. 13. Change the Access mode to Read and Write and ensure that the Make available
through Property Nodes and Create dynamic accessor options are selected as
shown below. Click on Create.
14. A Write Message String and Read Message String VI should be created for you, Close these and save to the folder Exercise 1
15. Right click Popup.lvclass in the project and select New>>VI for Override , then click OK (There is only one method to select, the Execute Method)
16. Go to the block diagram of the created VI. Delete the Call Parent Method VI and then use Ctrl B to delete the broken wires
17. Create more space in the centre of the block diagram and place a case structure. You
can do this by holding Ctrl, left clicking the mouse and dragging an area on the screen.
18. Wire it as shown below
19. Return to the No Error case. Drag a Read Message String in from your project and wire the Error lines and the Popup class wires through it.
20. Add a One Button Dialog from the functions palette, Programming>>Dialog &
User Interface>>One Button Dialog, then wire the Message String from the Read
Message String VI to the message input of the One Button Dialog VI.
21. Close the VI and save it in the Exercise 1 folder. Do NOT change the name of the VI. 22. Open the OOP Advanced with Commands VI from the Project Explorer. We will
call your new method from here.
23. Create a new Boolean button from the controls palette System>>Boolean>>System
Button. (This will keep the style of the Front Panel). Change the label to “Display
Message”.
24. Also create a string control. System>>String and Path>>System String. Change the label to “Message String”.
25. Switch to the Block Diagram. Navigate the Event Structure to “Frequency”:Mouse Up 26. Right click and Duplicate Event Case. Select “Display Message” and
27. Delete the control “Frequency 2”, the Write Frequency Message VI and the class
constant.
28. Drag Popup.lvclass and Write Message String.vi from the project into the event case. Move the “Message String” control into the case as well.
29. Wire the class constant to the “Write Message String” VI and then into the “Enqueue Element” VI. Wire the “Message String” control to the “Message String” input of the “Write Message String” VI.
30. Switch to the front panel and save then Run the VI. Enter a message and click the “Display Message” button. Your message will appear. If you Generate a signal, you must move the Frequency dial first to send the message.
Exercise 2
Concept – The aim of this exercise is to add a class to turn our function generator into an arbitrary waveform generator by loading in a waveform from a selection on disk. Add functionality with no architecture change.
1. Open the “OOP Advanced with Commands and Factory” VI from the project. Run this and experiment with the drop down box to load the different classes from disk and execute their methods. Note the options in the drop down box.
2. Stop the VI and close it.
3. In the project navigate to Classes>>Generation Class>>Generate Child Classes 4. Right click on “Generate Child Classes” and go to New>>Class
5. Name the class “Gen Arb” and click OK
6. Right click on Gen Arb.lvclass in the project and navigate to properties and then Inheritance.
7. Click Change Inheritance.
8. Select Generate.lvclass and then Inherit from Selected, then OK
9. Right click on Gen Arb.lvclass in the project and navigate to VI for Override... 10. Click OK. The only method available should be Generate.vi
11. Go to the block diagram of the created VI. Delete the Call Parent Method VI and then use Ctrl B to delete the broken wires.
12. Create more space in the centre of the block diagram and place a case structure. 13. Wire it as shown below
15. Go to Express>>Input>>File Dialog and drop this into the No Error case. Just click OK to the Dialog that pops up.
16. Drop down a Read From XML File. Programming>>File I/O>>XML>>LabVIEW
Schema>>Read from XML File. Select the String option in the polymorphic drop
down.
17. Drop down an Unflatten from XML VI. Programming>>File
I/O>>XML>>LabVIEW Schema>>Unflatten from XML.
18. Drop down a Waveform constant. Programming>>Waveform>>Analog Waveform>>Waveform Constant.
19. In the project navigate to Advanced Waveform.lvclass and then Waveform. Expand this and then drag in a Write Waveform method. Add an Enqueue Element VI from
Programming>>Synchronization>>Queue Operations>> Enqueue Element.
20.
a. Wire the Selected path of the File Dialog to the XML File Path of the Read from XML File.
b. Wire from XML Elements output of this VI to the xml string input of the Unflatten from XML VI.
c. Wire the waveform constant to the Type input of this VI.
d. Wire from the value of the Unflatten from XML VI to the waveform input of the Write Waveform VI.
e. Wire the Advanced Waveform class through the Write Wavefrom VI. Wire the Message Queue through the Enqueue Element VI.
f. Connect the Error Out of the Write Waveform VI to the Error In of the Enqueue Element VI.
g. In the project navigate to Message Child Classes. Drag the Display Message.lvclass into the VI.
