Why does this give a runtime error on the 2nd run after you undo?

[KasperFilipsen]

I'm working on a script where I select the nodes in layers and process them.

I noticed that if I run this script, it works fine, but if I then Undo and try to run it again. I now get a Runtime error: Attempt to access deleted scene object

(
	(LayerManager.current).nodes &theNodes
	maxOps.cloneNodes theNodes cloneType:#instance actualNodeList:&currentObjs newNodes:&newObjs
	select newObjs
)

Does the LayerManager not update after you undo?
Can you force it to update somehow?

My current workaround is to basically make a new array where I check for isValidNode on each node.

[klvnk]

don't get any issue with....

theNodes = #();
newObjs = #();
currentObjs = #();
(LayerManager.current).nodes &theNodes
maxOps.cloneNodes theNodes cloneType:#instance actualNodeList:&currentObjs newNodes:&newObjs
select newObjs

[KasperFilipsen]

Yeah, it seems to work fine if you run it in global scope, but as soon as you wrap it inside its own scope, it fails.

[klvnk]

nice not only do we have to solve the issue we have to second guess your code.  😕

[KasperFilipsen]

Yeah I apologize, I'm so used to running everything inside it's own scope I didn't think to wrap the example here. Edited.

[klvnk]

no probs grumpy monday morning 😉 adding a gc() before initializing the arrays seems to work btw,

though will cause issues if you do it twice in a row 😕

I think going with 

local temp = for n in theNodes where isValidNode n collect n;

after grabbing the layer nodes is still your best bet :?

[klvnk · Accepted solution]

the reason it works like this is, layers do not maintain a list of nodes they contain as such, instead each node in the scene maintains an reference to an *ILayer (the layer it's in). so 

(LayerManager.current).nodes

is initialized by iterating over the whole scene and collecting nodes in the current layer even deleted ones.

the mxs interface to layers has the following in its header description

This interface is a facade over disparate property sets on layers:

😕

you can do the same in mxs (but with out the deleted objects) with 

for i in objects where (refs.dependsOn i)[3] == LayerManager.current.layerAsRefTarg collect i;

though I wouldn't trust the hard [3] (it's actually 6 in the sdk so should be 7 😂 ) for all objects 🙂 

[denisT.MaxDoctor]

agree with Klvnk... 

for n in theNodes where isvalidnode n collect n is the solution

[denisT.MaxDoctor]

Great find by the way. I tweaked some of my methods because of this problem.

👍

[denisT.MaxDoctor]

---

@klvnk wrote:

for i in objects where (refs.dependsOn i)[3] == LayerManager.current.layerAsRefTarg collect i;

---

Probably faster and more reliable:

layer_ref = layermanager.current.layerasreftarg
for obj in objects where refs.DependencyLoopTest obj layer_ref collect obj

or

layer = layermanager.current
for obj in objects where obj.layer == layer collect obj

[klvnk]

it was more illustrative than serious 🙂  it's odd the .layer property isn't listed in the mxs help I use 😕

edit found it under INodeLayerProperties, weird that they list all the other properties of the INodeLayerProperties interface in the General Node Properties, displayByLayer, motionBylayer etc but not .layer !

[denisT.MaxDoctor]

After adding "nested" layers, things became more complicated and non-obvious. So I added my own MXS methods to get layer nodes with the optional "nested" argument.