Array of dictionaries in C#

Question

I would like to use something like this:

Dictionary<int, string>[] matrix = new Dictionary<int, string>[2];

But, when I do:

matrix[0].Add(0, "first str");

It throws " 'TargetInvocationException '...Exception has been thrown by the target of an invocation."

What is the problem? Am I using that array of dictionaries correctly?

Solution 1

Try this:

Dictionary<int, string>[] matrix = new Dictionary<int, string>[] 
{
    new Dictionary<int, string>(),
    new Dictionary<int, string>()
};

You need to instantiate the dictionaries inside the array before you can use them.

Solution 2

Did you set the array objects to instances of Dictionary?

Dictionary<int, string>[] matrix = new Dictionary<int, string>[2];
matrix[0] = new Dictionary<int, string>();
matrix[1] = new Dictionary<int, string>();
matrix[0].Add(0, "first str");

Solution 3

Dictionary<int, string>[] matrix = new Dictionary<int, string>[2];

Doing this allocates the array 'matrix', but the the dictionaries supposed to be contained in that array are never instantiated. You have to create a Dictionary object in all cells in the array by using the new keyword.

matrix[0] = new Dictionary<int, string>();
matrix[0].Add(0, "first str");

Solution 4

You've initialized the array, but not the dictionary. You need to initialize matrix[0] (though that should cause a null reference exception).

Solution 5

You forgot to initialize the Dictionary. Just put the line below before adding the item:

matrix[0] = new Dictionary<int, string>();

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Comments

[leppie]

Hmmm, you should get a NullReferenceException. Show more code.

[Adam Mihalcin]

Have you initialized matrix[0] to a new Dictionary<int, string>? Also, TargetInvocationException is part of the System.Reflection namespace. Where are you using reflection?

[Igor ostrovsky]

You can also simlpify "new Dictionary<int, string>[]" to just "new []"

[Aris]

simple and elegant!