Using Singleton Pattern to Retain Previous Variable Values?

Question

Is it possible using ExtendScript to retain the previous value of a property even after it has been updated by the user? I know after effects expressions update every frame, but I believe script values should be able to to persist. Is this sort of thing possible with ExtendScript?

I'm thinking something like this should be do-able using a singleton like pattern, but so far I have been unsuccessful. Heres what I've tried so far:

var instance;

//Check current instance value

alert(getInstance().value);

//Check if instance has a value, if not assign one, otherwise return current value

function getInstance(){

if(!instance){

instance = createInstance();

}

return instance;

}//End getInstance

//Create new object with a value and return it

function createInstance() {

var object = new Object(mySel.property("Effects").property("Transform").property(1));

return object;

}//End createInstance

Or, if singletons are the wrong approach is there any type of storage mechanism that can be called in ExtendScript to write values to?

Thanks!

UQg · Accepted Answer

I don't know one (which does not mean there is none), but maybe your problem could be simplified.

Your best luck would be that you want want to know whether the property is modified at all, in which case you can use p.isModified.

But if you want to know if it has been modified since last modification, then its another story. Properties objects can't be instantiated on their own, they are linked to actual properties in layers and can't be "frozen".

Brutal way :

If the property is suspected to have a bunch of keys, you'd be better of caching the stream of values in an array;

Else cache the keys (still lots of things to do...times, values, interpolations) and the expression, but then comparing two states can be uneasy.

.. for every p in your effect.

Hopefully you'll get a better answer

Xavier.

UQg · Answer

You createInstance function is a bit strange:

var p = app.project.activeItem.selectedProperties[0];

var a = new Object(p);

a==p; // true ===> point to the same property : if p is modified, a will be too

// and actually:

a===p; // true ===> a and p are exactly the same object

What are you trying to store ? The whole object ([object Property]) or the keyframable value (stream of numbers, arrays, etc) ?

Sign up

To post, reply, or follow discussions, please sign in with your Adobe ID.

Sign in to Adobe Community

To post, reply, or follow discussions, please sign in with your Adobe ID.

Scanning file for viruses.

This file cannot be downloaded