Removing something from a collection

Consider the following snippet:

//Remove all hexes that have a unit in them for (int i = 0; i < returnValue.Count; i++ ) { if (returnValue[i].CurrentUnit != null) { returnValue.RemoveAt(i); } } return returnValue;

This does not work.  For example, here is a screen shot:

image

The reason why is that the indexer is evaluated once,, but the list changes after each iteration.  In graphical terms:

0

1

2

3

4

5

X

X

0

1

2

3

4

X

 

 

Index 1 becomes Index 0, and since the loop is already on 1, it gets skipped for evaluation. What we need it to remove a hex and then keep looping – so the while construct needs to be used:

bool keepLooping = true; while (keepLooping == true) { int totalHexes = returnValue.Count; for (int i = 0; i < returnValue.Count; i++) { if (returnValue[i].CurrentUnit != null) returnValue.RemoveAt(i); if (totalHexes == returnValue.Count) keepLooping = false; } }

 

And the results work as expected:

image

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