List: ArgumentOutOfRangeException

Unity Engine
1

I’m trying to expand my knowledge of Lists and I’ve been experimenting the last few days. My current focus is on avoiding ArgumentOutOfRangeException: Argument is out of range errors when other functions or scripts are accessing a List that is constantly being updated.

Even checking if an element in a List is actually there before doing something can still result in these errors, so I am guessing between checking and doing, the List has changed.

Am I on the right track as to the cause? Or does anyone have some solid advice on how best to avoid out of index scenarios, or common causes?

Thanks!

2

How are you accessing your list(s)? Can you show some sample code?

3

That simply means you’re referring to an element that doesn’t exist. If the list.Count is 5, for example, then you can only use an index from 0-4. Anything else is out of range. That’s all there is to it.

That’s only possible if you changed the List yourself between checking and doing.

–Eric

4

Hi, thanks for the replies :slight_smile:

I have a script which is logging groups of vector3 information in a List. It’s elements are being removed, added, inserted and modified all the time. Groups are also being removed and added all the time.

The List uses a Class for it’s structure:

var testList = new List.<testClass>(); 

class testClass
{
	var id : String;
	var positions : List.<Vector3>();
}

I have an external script which is accessing (read only at the moment) elements of the list to display information.

It works but when I trigger lots of changes things get funky with:
NullReferenceException: Object reference not set to an instance of an object
…and…
ArgumentOutOfRangeException errors.

Have I found myself in some kind of data race?

I do check if an element exists before I try to do anything with it. For example

//groupPosition is the index number I am trying to retrieve
//positionNumber is the index number I am trying to retrieve

		if(testScript.testList.Count > groupPosition ) 
		{
			if(testScript.testList[targetPosition].positions.Count > positionNumber )
			{
				vector3Position = testScript.testList[targetPosition].positions[positionNumber] ;
			}
		}

Edit: After further testing it seems that trying positions.Count will error with a NullReferenceException as technically there is nothing there. Does this sound right? If so how would I check?

Edit 2: I have now added my own additional count in the class so I can keep track of how many positions there are. Not sure if the best solution but it works.

So all that leaves is the ArgumentOutOfRangeException errors.

Edit 3: Well I seem to have resolved the problems. Thanks for the inputs guys.