hashtable: snapshot out of sync

Questions & Answers
1

Hi, Im trying to create a tree-structure and am trying to delete some elements from the tree. I dont quite understand why the MyHashTable.Remove(#key) is causing this exepction:

InvalidOperationException: Hashtable.Enumerator: snapshot out of sync. System.Collections.Hashtable + Enumerator.FailFast()

the key does not have to be a string if i read it correctly? Im using ints as keys.

    protected var idListe : Hashtable = new Hashtable();

public function remove(nodeId:int){
    var startId = idListe[nodeId].getIdLeft();
    var targetId = idListe[nodeId].getIdRight();
    var endId = idListe[0].getIdRight();

    for (var item : DictionaryEntry in idListe){
        var id:int = item.Value.getId();
        var idLeft:int = item.Value.getIdLeft();
        var idRight:int = item.Value.getIdRight();

Debug.Log("Checking (" + nodeId + "):"+id+" => " +idLeft + " >= " + startId + " && " +idRight + " <= " + targetId);

        if (idLeft >= startId && idRight <= targetId){

Debug.Log("Deleting:"+id);

            idListe.Remove(id);     
        }
    }
    updateIdListe(startId ,endId,(targetId-startId));
}
3

This exception is being generated because you're removing items from `idListe` while you're iterating through it. Using a `foreach`-style loop as you have will only allow you to read the collection, but not modify it in any way.

The easiest way around this would be to assemble a temporary copy of the hashtable as you iterate through it, keeping the items that you require, then copy it back to `idListe` when you're finished.

2

I worked it out myself :)

the reference to the Hashtable in the for loop is still pointing to the current hash entry. If I remove the current index, the current for pointer seems to be pointing to nothing and therefore the hashtable is out of sync. So I need to make a list of elements to delete in the the for loop and delete them after the for loop seperately.