Populate array of objects from namevaluecollection in c#

Question

I am new to C#. Here is a hard-coded thing I got working:

InputProperty grantNumber = new InputProperty();
grantNumber.Name = "udf:Grant Number";
grantNumber.Val = "571-1238";

Update update = new Update();
update.Items = new InputProperty[] { grantNumber };

Now I want to generalize this to support an indefinite number of items in the Update object and I came up with this but it fails to compile:

Update update = BuildMetaData(nvc);  //call function to build Update object

and the function itself here:

private Update BuildMetaData(NameValueCollection nvPairs)
{
    Update update = new Update();
    InputProperty[] metaData;       // declare array of InputProperty objects
    int i = 0;
    foreach (string key in nvPairs.Keys)
    {
        metaData[i] = new InputProperty();      // compiler complains on this line
        metaData[i].Name = "udf:" + key;
        foreach (string value in nvPairs.GetValues(key))
            metaData[i].Val = value;
    }
    update.Items = metaData;
    return update;   // return the Update object
}

Answer 1

Since the size of your Items collection can vary, you should use a collection type like List<T> or Dictionary<K,V> instead of an array.

Answer 2

For the current compiler error, you need to initialize the metaData array, like:

InputProperty[] metaData = new InputProperty[](nvPairs.Count);

Using linq you could:

private Update BuildMetaData(NameValueCollection nvPairs)
{
    Update update = new Update();
    update.Items = nvPairs.Keys
        .Select(k=> new InputProperty
                    {
                       Name = "udf:" + k,
                       Val = nvPairs[k] // or Values = nvPairs.GetValues(k)
                    }
         )
        .ToArray();
    return update;      // return the Update object
}

Answer 3

If I'm not mistaken, your InputProperty array is never initialized. If you change line 2 to this:

InputProperty[] metaData = new InputProperty[nvPairs.Count];

That should fix it.

Answer 4

When you declared your array InputProperty[] metaData, you didn't initialize it. So when you tried to access a member, it just doesn't exist, which is why you got the error you did.

As Joel recommended, I'd advise you to look at the collection types provided in System.Collections.Generic for something suitable.