ok, my apologies. i guess my question is at what point to i check for dirty, and at what point do i insert the nulls?

Thanks for the reply - sorry to resurrect this post, but I am still struggling to put your advice to use. since I am mostly writing this plugin to learn, I'll go ahead and just paste the code in here ( please be gentle)

class CloneStalker (plugins.ObjectData):
def init (self):
self.SetOptimizeCache(True)

def Init(self, node):
    # Parameter initialization
    self.InitAttr(node, float, [c4d.CL_STALKER_MAX_NULLS])

    node[c4d.CL_STALKER_MAX_NULLS] = 100.0


    pd = c4d.PriorityData()
    if pd is None:
        raise MemoryError("Failed to create a priority data.")

    pd.SetPriorityValue(c4d.PRIORITYVALUE_MODE, 4)
    pd.SetPriorityValue(c4d.PRIORITYVALUE_PRIORITY, 100)
    node[c4d.EXPRESSION_PRIORITY] = pd


    return True


def CheckDirty(self, op, doc):

    frame = doc.GetTime().GetFrame(doc.GetFps())
    if frame != lastFrame:
        lastFrame = frame
        op.SetDirty(c4d.DIRTYFLAGS_DATA)

def AddToExecution(self, op, list) :  
    list.Add(op, c4d.EXECUTIONPRIORITY_GENERATOR, 400)  
    return True  



def GetVirtualObjects(self, op, hh):
    cloner = op[c4d.CL_STALKER_TARGET]
    doc = c4d.documents.GetActiveDocument()

    def GetStalkers(bname,tgt):
        allChild = tgt.GetChildren()
        stalkerChilds = []
        if allChild != None:
            for i in allChild:
                childname = i[c4d.ID_BASELIST_NAME]
                bnamelenght = len(bname)
                subname = childname[0:bnamelenght]
                if subname == bname:
                    stalkerChilds.append(i)

        return stalkerChilds

    if cloner != None:
        modata=mo.GeGetMoData(cloner)
        if modata != None:
            cache =  cloner.GetDeformCache()
            if cache is None:
                cache = cloner.GetCache()
            clones = cache.GetChildren()
            name = str(cloner[c4d.ID_BASELIST_NAME]) + ".Cloner Stalker"
            child_basename = op[c4d.ID_BASELIST_NAME].replace(".Cloner Stalker", ".Stalker.")

            if cloner.GetNext() != op:
                op.InsertAfter(cloner)
            null= c4d.BaseObject(c4d.Onull)
            null[c4d.NULLOBJECT_DISPLAY]=0
            null[c4d.ID_BASELIST_NAME] = name
            parent=op
            

            md = mo.GeGetMoData(cloner)
            marr = md.GetArray(c4d.MODATA_MATRIX)
            count = md.GetCount()
            Selection = []
            maxNulls = op[c4d.CL_STALKER_MAX_NULLS]
            lastChild = None
            child = GetStalkers(child_basename,op)
            if mo.GeGetMoDataSelection(cloner) == None:
                for i in range(count):
                    Selection.append(i)
                selected=Selection
            if  mo.GeGetMoDataSelection(cloner)!= None:
                Selection = mo.GeGetMoDataSelection(cloner).GetAll(count)
                selected=[i for i,x in enumerate(Selection) if x==1]

            if op[c4d.ID_BASELIST_NAME]!=name:
                child_basename = op[c4d.ID_BASELIST_NAME].replace(".Cloner Stalker", ".Stalker.")
                if len(child)>0:
                    for i in child:
                        old_name =i[c4d.ID_BASELIST_NAME]
                        index_name = old_name[len(child_basename):len(old_name)]
                        n_name = cloner[c4d.ID_BASELIST_NAME] + ".Stalker." + index_name
                        i[c4d.ID_BASELIST_NAME] = n_name
                        print (n_name)
                
                op[c4d.ID_BASELIST_NAME] = name
                child_basename = op[c4d.ID_BASELIST_NAME].replace(".Cloner Stalker", ".Stalker.")
                child = GetStalkers(child_basename,op)    
                parent=op
            op.SetMg(cloner.GetMg())

            if len(child)<len(selected) and len(child) < maxNulls:
                currChilds=[]
                for i in child:
                    child_name = i[c4d.ID_BASELIST_NAME]
                    nameLenght = len(child_name)
                    index = int(child_name[len(child_basename):nameLenght])
                    currChilds.append(index)
                new = [item for item in selected if item not in currChilds]
                for i in new:
                    obj= c4d.BaseObject(c4d.Onull)
                    obj[c4d.ID_BASELIST_NAME] = child_basename + str(i)
                    obj[c4d.NULLOBJECT_DISPLAY]=3
                    obj[c4d.NULLOBJECT_RADIUS]=50
                    extCompTag = c4d.BaseTag(465000402)
                    matrix = clones[i].GetMg()
                    obj.SetMg(matrix)
                    obj.InsertTag(extCompTag)
                    if len(child)>0:
                        lastChild = child[(len(child)-1)]
                    doc.InsertObject(obj,parent,lastChild)
                    child = GetStalkers(child_basename,op)
                    if len(child)==maxNulls:
                        break
            if len(child)>len(selected) or len(child)>maxNulls:
                for i in child:
                    child_name = i[c4d.ID_BASELIST_NAME]
                    nameLenght = len(child_name)
                    index = child_name[len(child_basename):nameLenght]
                    if not int(index) in selected:
                        i.Remove()
                    child = GetStalkers(child_basename,op)
                while len(child)>maxNulls:
                    lastChild = child[(len(child)-1)]
                    lastChild.Remove()
                    child = GetStalkers(child_basename,op)
                    
           
               
def Execute(self, op, doc, bt, priority, flags) :
    
    def GetStalkers(bname,tgt):
        allChild = tgt.GetChildren()
        stalkerChilds = []
        if allChild != None:
            for i in allChild:
                childname = i[c4d.ID_BASELIST_NAME]
                bnamelenght = len(bname)
                subname = childname[0:bnamelenght]
                if subname == bname:
                    stalkerChilds.append(i)

        return stalkerChilds
    cloner = op[c4d.CL_STALKER_TARGET]
    doc = c4d.documents.GetActiveDocument()
    name = str(cloner[c4d.ID_BASELIST_NAME]) + ".Cloner Stalker"
    child_basename = op[c4d.ID_BASELIST_NAME].replace(".Cloner Stalker", ".Stalker.")
    parent=op
    child = GetStalkers(child_basename,op)
    Selection = []

    if cloner != None:
        modata=mo.GeGetMoData(cloner)
        if modata != None:
            cache =  cloner.GetDeformCache()
            if cache is None:
                cache = cloner.GetCache()
            clones = cache.GetChildren()
            md = mo.GeGetMoData(cloner)
            marr = md.GetArray(c4d.MODATA_MATRIX)
            count = md.GetCount()

            if mo.GeGetMoDataSelection(cloner) == None:
                for i in range(count):
                    Selection.append(i)
                    selected=Selection
            if  mo.GeGetMoDataSelection(cloner)!= None:
                Selection = mo.GeGetMoDataSelection(cloner).GetAll(count)
                selected=[i for i,x in enumerate(Selection) if x==1]

            for x in selected:
                matrix = clones[x].GetMg()
                ch_name = child_basename + str(x)
                obj=c4d.documents.BaseDocument.SearchObject(doc,ch_name)
                obj.SetMg(matrix)
                print (clones[x].IsDirty(1))
    return c4d.EXECUTIONRESULT_OK        

Please feel free to advise what i am doing wrong here, and what shuold i be doing instead.

many thanks for your patience.
cheers
Eddie

Hi All,
I'm on my first plugin, and by no means a true Python developer.
my plugin is relatively simple : it gets a cloner from a LINK box in the GUI, and creates a null for each clone, with a compositing tag attached, and gets the matrix of each clone from the GetCache() and applies it to each null, making them follow the clones.

It all works fine on the viewport, but if i export an AEC file, the nulls are all static, and not following changes caused by effectors, like position or rotation etc. it DOES work on the viewport as you scrub the timeline in C4D though.

i'm creating the Nulls during the GetVirtualObjects() function, and changing their Matrix on the Execute() function.

Any ideas?

Cheers,
Eddie

Apologies if this has been answered before, but I could not find it by searching.

my plugin makes a null follow the matrix of another object. problem is that because of priorities unless the plugin object is after the "target" it is always one frame behind ( or it snaps on position when you refresh the viewport)

my plugin is based on ObjectData, and is a Generator, not a tag, so how do I go about changing the priority so that the code only runs after the target's matrix has been calculated?

i'd much appreciate a "dummies" explanation, as I am still only dipping my toes into programming and plugin dev

Many thanks,
Eddie