How to set array length in c# dynamically

Question

I am still new to C# and I\'ve been struggling with various issues on arrays. I\'ve got an array of metadata objects (name value pairs) and I would like to know how to creat

Answer 1

Does is need to be an array? If you use an ArrayList or one of the other objects available in C#, you won't have this limitation to content with. Hashtable, IDictionnary, IList, etc.. all allow a dynamic number of elements.

Answer 2

You can create an array dynamically in this way:

 static void Main()
    {
        // Create a string array 2 elements in length:
        int arrayLength = 2;
        Array dynamicArray = Array.CreateInstance(typeof(int), arrayLength);
        dynamicArray.SetValue(234, 0);                              //  → a[0] = 234;
        dynamicArray.SetValue(444, 1);                              //  → a[1] = 444;
        int number = (int)dynamicArray.GetValue(0);                      //  → number = a[0];


        int[] cSharpArray = (int[])dynamicArray;
        int s2 = cSharpArray[0];

    }

Answer 3

Typically, arrays require constants to initialize their size. You could sweep over nvPairs once to get the length, then "dynamically" create an array using a variable for length like this.

InputProperty[] ip = (InputProperty[])Array.CreateInstance(typeof(InputProperty), length);

I wouldn't recommend it, though. Just stick with the

List<InputProperty> ip = ...
...
update.Items = ip.ToArray();

solution. It's not that much less performant, and way better looking.

Answer 4

Or in C# 3.0 using System.Linq you can skip the intermediate list:

private Update BuildMetaData(MetaData[] nvPairs)
{
        Update update = new Update();
        var ip = from nv in nvPairs
                 select new InputProperty()
                 {
                     Name = "udf:" + nv.Name,
                     Val = nv.Value
                 };
        update.Items = ip.ToArray();
        return update;
}

Answer 5

Use Array.CreateInstance to create an array dynamically.

    private Update BuildMetaData(MetaData[] nvPairs)
    {
        Update update = new Update();
        InputProperty[] ip = Array.CreateInstance(typeof(InputProperty), nvPairs.Count()) as InputProperty[];
        int i;
        for (i = 0; i < nvPairs.Length; i++)
        {
            if (nvPairs[i] == null) break;
            ip[i] = new InputProperty();
            ip[i].Name = "udf:" + nvPairs[i].Name;
            ip[i].Val = nvPairs[i].Value;
        }
        update.Items = ip;
        return update;
    }

Answer 6

Use this:

 Array.Resize(ref myArr, myArr.Length + 5);