Nested Lists "Add" method problem

Question

Hello there,

for reasons I need a List of Vector2-Lists:

 List<List<Vector2>> occludedObjects;
     
 void someInitFunction(){
     occludedObjects = new List<List<Vector2>>();
     List<Vector2> occludedPoints = new List<Vector2> ();
     occludedObjects.Add (occludedPoints);
 }

Now when I add a new Vector2 to a sublist, every sublist will overwrite it's content with this Vector2. Clearing any sublist seems to clear the other sublists, too. Here is how I'm trying to do things:

 occludedObjects[0].Clear();
 occludedObjects[0].Add (new Vector2(0f, 0f));
 occludedObjects[0].Add (new Vector2(0f, 1f));

I guess I am missing some basic nested lists business :( If this is not the source of the problem, i will try and dig deeper into my script.

Help (especially noob friendly) is very, very appreciated!

Answer 1

Best Answer

Answer by Dave-Carlile · Jun 28, 2015 at 07:11 PM

This is adding the exact same list instance each time...

  List<Vector2> occludedPoints = new List<Vector2> ();
  occludedObjects.Add (occludedPoints);

They all point to the same object, so it doesn't matter which object reference you use, it's going to add to the same list. You need to create a new instance each time, so...

  occludedObject.Add(new List<Vector2>());

Now each list entry in occludedObjects will point to a separate instance.

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RyFridge · Jun 29, 2015 at 07:58 AM 0

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Wow, thank you so much. It works perfectly. I thought it would add a new copy / instance of the "occludedPoints" List, not reference back to it. But it's totally logical.

Now I feel really stupid :)

Nested Lists "Add" method problem

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