Error using foreach in a dictionary that contains objects as a value

Question

I am trying to iterate over a dictionary containing objects as a value:

foreach (KeyValuePair<int, CMapPool_Entry> Entry in MapPool) { this.SendConsoleMessage(Entry.Value.Map); } 

Below you can see the CMapPool_Entry class

 public class CMapPool_Entry { public string Map; public string Mode; public int Rounds; public int Index; public int Votes; public bool Nominated; public string Nominator; public CMapPool_Entry(string map, string mode, int rounds, int index, string Nominator_LeaveEmptyStringIfNone) { this.Map = map; this.Mode = mode; this.Rounds = rounds; this.Index = index; // If Nominator isn't empty, set map to nominated if (Nominator_LeaveEmptyStringIfNone != "") { this.Nominated = true; this.Nominator = Nominator_LeaveEmptyStringIfNone; } } public void AddVote() { this.Votes++; } public void RemoveVote() { if (this.Votes > 0) this.Votes--; } } 

Here you can also see the SendConsoleMessage method:

  private void SendConsoleMessage(string message) { this.ExecuteCommand("procon.protected.pluginconsole.write", String.Format("{0}", message)); } 

It seems to me that this will work, I read about how editing the values ​​from the dictionary inside foreach will give the following error: "The collection has been changed, the enumeration operation cannot be performed."

But why am I getting this error? I am not editing any values, am I just reading them correctly? It works fine if CObject was a string or int instead, but if it is an object, it goes out. What am I doing wrong, what should I do?

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EDIT: after further debugging, I noticed that Entry.Key is fine, but as soon as I touch Entry.Value, I get errors. For some reason, I accidentally got two different errors:

• "The collection has been modified; an enumeration operation cannot be performed.
• "This key is not in the dictionary.

Any ideas? Or enumerating dictionaries with objects as values ​​just doesn't work?

Answer 1

As stated in the comments, you are modifying the dictionary in another thread while you are trying to read it. You wrote in the comments that you “copied” the Dictionary by writing:

 Dictionary<int, CMapPool_Entry> MapPool = this.Votemap_MapPool; 

This does not copy the dictionary, but creates a link to Votemap_MapPool in MapPool , so when you change Votemap_MapPool somewhere in your code when reading MapPool you will get a System.InvalidOperationException with the message that the collection has been changed.

To really copy the dictionary, you need to write:

 Dictionary<int, CMapPool_Entry> MapPool = new Dictionary<int, CMapPool_Entry>(Votemap_MapPool); 

This really creates a new instance of the dictionary with Votemap_MapPool as content, and when Votemap_MapPool changes, MapPool untouched.

Answer 2

You cannot change the collection (also as a dictionary library) during foreach processing.

Workaround:

 using System.Linq; foreach (CObject value in ExampleDictionary.Values.ToArray()) { this.SendConsoleMessage(value.SomeVariableInObject); }