Erase! gives an error: can't find parent

daiku

Has anyone ever gotten an error like this:

Error: #<TypeError: Cannot determine parent of entity>

Here's the line of code:

sel.each {|e| e.erase! }

Even if sel is empty, I shouldn't get an error. As it happens, it's got the whole model in it, except for a few component instances.

Here's a larger code snippet:

sel.clear
model.entities.each {|e| sel.add(e)}
shop_dwg.each {|dwg| sel.remove(dwg)}
sel.each {|e| e.erase! }

I'm trying to erase everything but the shop_dwg comps. This code normally runs fine, but I've got a model that usually (but not always?) give me this error. CB.

brad

Hi Clark,

I have seen similar error messages like this before.

Try this:

Start a new model
Drag in a component from the component broswer
Bring up the Ruby Console
Type in: Sketchup.active_model.definitions[0].erase! > Enter

Is this the same error message you are getting?

Please let me know.

Thank you.

daiku

Brad:

Yes, that's exactly the same error message I'm getting. But in my case, I'm not trying to erase a definition - I'm trying to erase entities. Your suggestion gave me an idea, though. I typed this in the console:

Sketchup.active_model.entities.each {|e| e.erase!}

This gave an odd behavior: some of my model gets erased, but not all. If I then execute the same line again, more disappears. After about 8 times, it's finally all gone. Is the list somehow getting rearranged out from under me as I erase things (thus hosing up the "each" method)?

RickW

Clark,

Does the error line correspond to the erase! command? Or is it pointing to a different portion of your code?

RickW

Clark,

Yes, as you erase edges that bound faces, the face is removed from the selection automatically (since it no longer exists), and the objects' indices are shifted accordingly.

Given sel=model.selection followed by sel.each{|e| e.erase!}:

The script erases sel[0], an edge. That edge bounded a face at sel[1]. This shifts the object at sel[2] to sel[0], which is then ignored because the .each loop has already finished working on sel[0] and moved on to sel[1].

Furthermore, faces aren't the only culprits. Erasing anything could cause the next entity to be shifted to its index location, thus you can miss about 1/2 of the entities on any given pass of selection.each.

Better to add the selection entities to an array and cycle through the array rather than rely on selection.each

brad

Thanks for jumping in Rick.

That is a great suggestion about adding them to an array and cycling through the array indexes.

daiku

Thanks Guys.

Yes, I can see now why it's happening, and also why it happens on this model and not others. Most of my models are components only.

But if I add the entities to my own array, and then erase them all, won't I run into a similar problem? If I erase an edge before I get to the face, I'll still try to erase the face, but it will be gone from the model.

The reason I'm using the selection is that it's easy to add all the entities to it. There's a sel.add that doesn't care what kind of thing I'm adding. If I make my own entities array, I have to know what each thing is and call the right add, as there's no generic add. CB.

tbd

also check with entity.valid? before doing stuff on an entity like this:

all_ent = []
Sketchup.active_model.entities.each do |ent|
  all_ent.push ent
end
all_ent.each {|ent| x.erase! if ent.valid?}

daiku

That's the stuff! Thanks, guys. All better now. CB.

TIG

Sketchup.active_model.entities.to_a.each{|e|e.erase! if e.valid?}

is a bit shorter and does the same...

RickW

Clark,

@unknownuser said:

The reason I'm using the selection is that it's easy to add all the entities to it. There's a sel.add that doesn't care what kind of thing I'm adding.

True, but .erase! does care what you're erasing (as you discovered), so you're still in the same boat with type checking. In fact, that's really the bottom line: check everything and assume nothing.

It's a hassle, but it's necessary, because inevitably someone will come along and provide unexpected input, and things will error out.

Regards, and happy coding!

daiku

TIG: to_a == Make into array? Undocumented or standard ruby?
Rick: I can add any kind of item to a generic array. I was stuck on using the entities container for some reason. Your cautionary point is well made.

Thanks, guys. CB.

RickW

Standard ruby conversion methods include (but are not limited to):
.to_a - convert to an array
.to_i - convert to an integer
.to_f - convert to a float
.to_s - convert to string

Though standard ruby, they may not be applicable to all data types. SU adds more .to_n methods:

.to_feet - convert a number of inches to feet
.to_yard - convert a number of inches to yards
.to_mile - convert a number of inches to miles
.to_m - convert a number of inches to meters
.to_cm - convert a number of inches to centimeters
.to_mm - convert a number of inches to millimeters
.to_km - convert a number of inches to kilometers

.feet - convert a number of feet to inches
.yard - convert a number of yards to inches
.mile - convert a number of miles to inches
.m - convert a number of meters to inches
.cm - convert a number of cm to inches
.mm - convert a number of mm to inches
.km - convert a number of km to inches

There are also .inch and .to_inch methods, but since SU internal units are inches, these are almost never used (but are included, I think, for consistency).