LabVIEW learning note 9: capture the "value change" event generated by the program modifying the control value

Problems encountered , I simplified this problem into a vi, There is 2 An OK button （ Mechanical action ： Triggered after clicking ）, Use the event structure （ Value change ） A light is controlled to light up .

I hope to achieve ： I click a button a Rear control a lamp a Light up （ It represents some data calculation ）, Judging by the results of these calculations , After judging, let another button b Also trigger （ The event structure of another button is also value change ）, then b The light is on . In this process, I just click the button a, It looks like you clicked the button a Then I clicked the button b（ Actually, there is no button b）
ps： For some reason , Can't take a,b Change the value of and put it into the same event Branch , You can't put two lights in the same event structure .

  I didn't understand , Forced to change a program writing , Later, I happened to see a series of tycoons on the Internet , It's like being enlightened .

LabVIEW Can't catch the error caused by the program modifying the control value “ Value change ” event _LabVIEW Developed blog -CSDN Blog _labview Output value change triggers an event

When using event structures , Respond to the value change event of a display control in the front panel in the event branch , The display control dynamically changes its value in other parts of the program .VI When it's running , It can be observed that the value of the display control has been changed , But the corresponding event branch does not execute . Why is there no response in the event structure to the value change event of the display control ？

answer :

The event structure only registers events generated by direct front panel user input , And in the problem , The value of the display control is not entered by the user, but changed by the program , So this is “ Value change ”LabVIEW Won't catch , Therefore, it cannot respond to the corresponding event Branch . and , Even if you use the program VI The server , Global variables , Local variables, etc VI And front panel controls ,“ Value change ” Events will not be LabVIEW capture .

There is one exception , The events of the input control and the display control can be controlled by calling the value （ The signal ） The attribute node of . This property is write only , Every time the attribute node is written, it is like the user's operation on the front panel changes the value . It should be noted that , When using this property in a loop , If the attribute is written every time in the loop iteration , Regardless of whether the control actually has a value change , The program will generate a set of value change events .
 

Refer to the picture below and the... In the attachment VI.

In the above example , The event structure is used to capture the input control to connect to Numeric Of Event Source Displays the name of the control “ Value change ” event .

In the event structure Numeric“ Value change ” In the branch Numeric Assign a new value to Event Source , Instead of directly outside the event structure Numeric Connect to Event Source, This can avoid every time Event Source A change in the value of “ Value change ” event . once Numeric The value has changed , The corresponding event branch will respond , adopt Event Source Value （ The signal ） The attribute node can generate Event Source Of “ Value change ” event , His corresponding event branch also performs , As shown in the figure below .

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