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I'm trying to create a Dictionary with array of integer, string and boolean data types as values. I figured, I should use object[] as value, so declaration would look so:

Dictionary<long, object[]> netObjectArray = new Dictionary<long, object[]>();

Whenever I try setting its element's value to something, VS says there was no such key found in the dictionary.

netObjectArray[key][2] = val; // ex: The given key was not present in the dictionary.

How do I work with this correctly?

UPD1: Somehow, right before throwing this exception, the other dictionary is used without problems in a similar way:

Dictionary<long, Vector2> netPositions = new Dictionary<long, Vector2>();
netPositions[key] = new Vector2(x, y); // works ok

After this locals show the value was assigned and dictionary now contains that entry. Why is this not the case with my other dictionary?

Solution: Before writing a value to an array of values, we must first initialize that array. This code works for me:

try { netObjectArray[key] = netObjectArray[key]; } // if the object is undefined,
catch { netObjectArray[key] = new object[123]; } // this part will create an object
netObjectArray[key][0] = new Vector2(x, y) as object; // and now we can assign a value to it :)
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  • 3
    Have you initialized netObjectArray[key] to at least new object[2]? Commented Apr 10, 2012 at 20:19
  • 3
    Besides, storing different types like this in a Dictionary is a bad code smell. Do you really need that, or can you encapsulate the data in a better format? Commented Apr 10, 2012 at 20:22
  • You could use a Tuple<int,string,bool> as value instead. msdn.microsoft.com/en-us/library/system.tuple.aspx Commented Apr 10, 2012 at 20:25
  • 7
    @user1306322 Create a Player class with all of that info, and have a Dictionary of Players. Commented Apr 10, 2012 at 20:28
  • 1
    @Servy I wish I could upvote your comment multiple times: this is precisely the case when arrays are bad and classes are excellent. Commented Apr 10, 2012 at 20:29

3 Answers 3

Reset to default
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This is expected: if the key is not present in the Dictionary<K,V>, an attempt to read at that key fails. You should assign an empty array to the element at the key before accessing it.

Here is the typical pattern of accessing a dictionary when you do not know if the key is present or not:

object[] data;
if (!netObjectArray.TryGetValue(key, out data)) {
    data = new object[MyObjCount];
    netObjectArray.Add(key, data);
}
data[2] = val;

EDIT (in response to the edit of the question)

You see an exception only when you try reading the dictionary at the previously unknown key. Assignments such as yours

netPositions[key] = new Vector2(x, y);

are allowed, even though the key is not in the dictionary at the time of the assignment: this performs an "insert or update" operation on your dictionary.

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4 Comments

Then how does netPositions[key] = new Vector2(x, y); not cause exception, while netObjectArray[key][2] = val; which goes right next, does? Is it the new part which is allowed and simply setting is not?
@user1306322 Please see my edit. Essentially, reading an unknown key is not allowed, but writing an unknown key is OK.
My comment was response to your edit. As I understand, I'm writing consecutively to two previously undefined values. You are saying to have that exception thrown, I need to try reading an undefined value at selected position, but I am not doing it anywhere in the code. ok, false alarm the answer is in the comment below [stackoverflow.com/questions/10095835/…
@user1306322 You do perform a read, but in an obscure way: netObjectArray[key][2] = val is equivalent to (netObjectArray[key])[2] = val, and the netObjectArray[key] is an attempt to read an array of objects at the key. The write part of the assignment operation goes against the object array that you fetch.
1

Try something like this:

Dictionary<long, object[]> netObjectArray = new Dictionary<long, object[]>();
for (int i = 0; i < 100; i++) netObjectArray[i] = new object[100];//This is what you're missing.
netObjectArray[key][2] = val;
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5 Comments

Can you explain why am I missing it in the array dictionary and the usual dictionary works fine without it?
My guess is: In your Dictionary<long, Vector2> you're putting a Vector2 in netPositions[key], which is what you're supposed to do. In Dictionary<long, object[]> you're not putting an object[] in netObjectArray[key] (which is what you're supposed to do) at all. You're skipping a step. You're trying to access a nonexistent object[].
Yes, I'm trying to write a value to previously undefined array of said values. Good eye.
@user1306322 Assuming I understand correctly that the long is the player-number and that you now want to 'initialize' a new player: Add: long numberOfPlayers = 0; somewhere. And then: void AddPlayer() { netObjectArray[numberOfPlayers++] = new object[100]; }//Note: numberOfPlayers will only be increased after the action. As needed.
@user1306322 But I would actually advise going with Servy's advice of creating a class for each player's 'properties'.
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Dictionary<string, object[]> complex = new Dictionary<string, object[]>();

complex.Add("1", new object[] { 1, 2 });

object[] value = complex["1"];
value[1] = val;

works for me...

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