Question

I’m looping through an array of items nested within another array of items.

Almost always, the inner array contains 5 indexes, but there is an off chance that the feed I’m consuming will only have 4 indexes in it.

When I add the indexes to my ViewModel, if the fifth index is missing, everything blows up.

How can I prevent “Index is outside the bounds of the array” errors in this specific scenario?

private List<ImageViewModel> ConvertSmugMugModel(SmugMugGallery smugMugGallery)
{
    return smugMugGallery.Channel.Items.Select(i => new ImageViewModel
        {
            TinyImage = i.Group.Contents[0].Url, 
            ThumbnailUrl = i.Group.Contents[1].Url, 
            SmallImageUrl = i.Group.Contents[2].Url,
            MediumImageUrl = i.Group.Contents[3].Url,
            LargeImageUrl = i.Group.Contents[4].Url
        }).ToList();
}

*note: I’m not opposed to moving to an iCollection or some other object if using an array is not the best fit. I just didn’t want to add bloat if I didn’t need to.

---

Edit

Kal asked what the the model looks like in a comment below.

[XmlRoot("rss")]
public class SmugMugGallery
{
    [XmlElement("channel")]
    public m_Channel Channel { get; set; }
    public class m_Channel
    {
        [XmlElement("item")]
        public Item[] Items { get; set; }
        public class Item
        {
            [XmlElement("group", Namespace = "http://search.yahoo.com/mrss/")]
            public m_Group Group { get; set; }
            public class m_Group
            {
                [XmlElement("content", Namespace = "http://search.yahoo.com/mrss/")]
                public Content[] Contents { get; set; }
                public class Content
                {
                    [XmlAttribute("url")]
                    public string Url { get; set; }
                }
            }
        }
    }
}

Answer 1

My first thought is just use the ? operator, like so:

    private List<ImageViewModel> ConvertSmugMugModel(SmugMugModel smugMugGallery)
    {
        return smugMugGallery.Channel.Items.Select(i => new ImageViewModel
        {
            TinyImage = i.Group.Contents[0].Url,
            ThumbnailUrl = i.Group.Contents[1].Url,
            SmallImageUrl = i.Group.Contents[2].Url,
            MediumImageUrl = i.Group.Contents[3].Url,
            LargeImageUrl = i.Group.Contents.Count() > 4 ? i.Group.Contents[4].Url:new Url("blank")
        }).ToList();
    }

You may also want to put that check into the rest of them also, unless you’re 101% sure you won’t run into less than 4 elements. Thusly:

    private List<ImageViewModel> ConvertSmugMugModel(SmugMugModel smugMugGallery)
    {
        return smugMugGallery.Channel.Items.Select(i => new ImageViewModel
        {
            TinyImage = i.Group.Contents.Count() > 0 ? i.Group.Contents[0].Url:new Url("blank"),
            ThumbnailUrl = i.Group.Contents.Count() > 1 ? i.Group.Contents[1].Url:new Url("blank"),
            SmallImageUrl = i.Group.Contents.Count() > 2 ? i.Group.Contents[2].Url:new Url("blank"),
            MediumImageUrl = i.Group.Contents.Count() > 3 ? i.Group.Contents[3].Url:new Url("blank"),
            LargeImageUrl = i.Group.Contents.Count() > 4 ? i.Group.Contents[4].Url:new Url("blank")
        }).ToList();
    }