Argument Exception: "An item with the same key has already been added"

Question

1.00/5 (1 vote)

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I have an application which got hung when i tried to add items to it.

I get a runtime error:

An item with the same key has already been added.

C#

  private class ProductUpdate
        {
            public int Index = 0;
            public string ProductCode;
        }
private void UpdateProduct( List<string> account, string userEmail, 
List<Product> products )
   {
Dictionary<string, ProductUpdate> productUpdateDictionary = new Dictionary<string, ProductUpdate>();

            for ( int i = 0; i < products.Count; i++ )
            {
       productUpdateDictionary.Add( products[i].code, new ProductUpdate { Index = i, ProductCode = products[i].code } );
            }
}

I don't know how to solve this issue ,any body has any suggestion
Thanks a lot!

Posted 17-Mar-15 10:48am

KRI19

Updated 17-Mar-15 10:55am

v2

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Comments

Maciej Los 17-Mar-15 16:51pm

"What did i do wrong?" You're trying to add value which already exists. Dictionary Key can not be duplicated.

3 solutions

Solution 1

There's no bug in the code that you posted. The problem is either of conceptual kind or lies in the code that calls UpdateProduct(..).

In this line:

C#

productUpdateDictionary.Add( products[i].code, new ProductUpdate { Index = i, ProductCode = products[i].code } );

your code is populating a Dictionary. A Dictionary only ever allows unique keys to be added. One or more Products in the method-argument List<Product> products have identical codes and that's the cause of the exception here.

Edit: <> troubles

Posted 17-Mar-15 10:56am

manchanx

Updated 17-Mar-15 11:15am

v3

Comments

Maciej Los 17-Mar-15 17:00pm

Nice explained, +5!

[no name] 17-Mar-15 17:15pm

Merci :-)

Maciej Los 17-Mar-15 17:22pm

I thought you're a German, but you behave like a Frenchman ;)
Cheers from Poland, Maciej

[no name] 17-Mar-15 17:27pm

hehe.. tylko dla zabawy ;)
Cheers from Hamburg - Sebastian

Maciej Los 17-Mar-15 17:31pm

Oh no, you're Pole too ;)

[no name] 17-Mar-15 17:34pm

I'm of every nationality that's available at translate.google.de ;)
Though I understood that A LITTLE as I learned Russian a long time ago.

Maciej Los 17-Mar-15 17:45pm

:laugh:
Ich lernte Deutsche sprache 4 jahres aber das war viele jahres zurück. Now, i'm almost not able to use it. I understand much if person which communicates with me says words slower then usually. ;) English... i never learn it, but...

[no name] 17-Mar-15 17:54pm

Das war doch ganz gut :)

KRI19 17-Mar-15 17:17pm

Thanks a lot! great expplanation

[no name] 17-Mar-15 17:24pm

You're welcome!

Solution 2

Please, read my comment to the question.

A dictionary[^] does not allow to add the same value twice. You need to handle it by adding Try... Catch... Finally[^] block.

Posted 17-Mar-15 10:59am

Maciej Los

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John C Rayan · Accepted Answer · 2015-03-17T11:06:00

Solution 3

You have to check if a key already exists before adding a value for the key. You have to do as follows.

SQL

if (!productUpdateDictionary.Contains(products[i].code)){
    productUpdateDictionary.Add(products[i].code, new ProductUpdate { Index = i, ProductCode = products[i].code });
}

Posted 17-Mar-15 11:06am

John C Rayan

Comments

KRI19 17-Mar-15 17:17pm

It just worked fine. Thanks you saved my Day

[no name] 17-Mar-15 17:23pm

Note that this avoids the exception but it's not a universal solution: If you don't expect your Products-List to contain duplicates, you're just hiding the error here. If you're fine with filtering out the duplicates, it's alright to do it like this.