Dropdown in perspective

Ignition
,
1

Hello,
In Perspective, I would like to trigger a script when a value is deleted from a dropdown.

I don't know the name of the event.

Thank you

2

Do you mean when an item is no longer available in the options property, or when someone hits a clear button to set the selected value to None?

3

Hi,

The event when someone press the cross in the value of the dropdown

Capture d’écran 2025-11-11 153731

4

Since those are stored in props.value parameter and you want to trigger only when something is deleted, I would use a change script on props.value. Then compare the length of previousValue.value and currentValue.value to see if something was removed from it

def valueChanged(self, previousValue, currentValue, origin, missedEvents):
	# grab the previous and current array length, default to 0 if null
	previousLen = len(previousValue.value) if previousValue.value else 0
	currentLen = len(currentValue.value) if currentValue.value else 0
	
	# if array length reduces
	if previousLen > currentLen:
		# default current array to [] in case of null
		currentValueArray = currentValue.value or []
		# find the difference aka whatever was removed if needed
		difference = [value for value in previousValue.value if value not in currentValueArray]

		system.perspective.print('Array length reduces from %s to %s' % (previousLen, currentLen))
		system.perspective.print(difference)
2 Likes
5

Thank you for your reply, sorry but where must I write the script ?

6

Right click on the value prop in the property editor, then you’ll see the option to add a change script.

1 Like
7

Thanks for your help

Regards

8

Hello,

If the dropdown is empty, the previousValue has no value.How to fix it?

Thanks

9

What is the error message?

10

'NoneType' object has no attribute 'value'

11

Just test for it. Something like,

def valueChanged(self, previousValue, currentValue, origin, missedEvents):
	if not previousValue:
		return
	# grab the previous and current array length, default to 0 if null
	previousLen = len(previousValue.value) if previousValue.value else 0
	currentLen = len(currentValue.value) if currentValue.value else 0
	etc.
2 Likes