Getting a NullReferenceException error while rendering a multilist field value

Question

I am trying to create a carousel in Sitecore 8.2. I have created a carousel item with the Image and Text fields and these carousel items are mapped to Multilist.

I am getting a null reference error while rendering the multilist items in Visual Studio.

My View code:

<div id="home-carousel" class="jcarousel-wrapper">
<a href="#" class="jcarousel-control-prev">&lsaquo;</a>
<a href="#" class="jcarousel-control-next">&rsaquo;</a>

<div class="jcarousel carousel-stage">
<asp:Repeater ID="rptCarousel" ItemType="Sitecore.Data.Items.Item" runat="server">
<HeaderTemplate>
<ul class="carousel">
</HeaderTemplate>

<ItemTemplate>
<li>
<sc:Image Field="Carousel Image" Item="<%# Container.DataItem %>" runat="server" />
<sc:Text Field="Carousel Text" Item="<%# Container.DataItem %>" runat="server" />
</li>
</ItemTemplate>
<FooterTemplate>
</ul>
</FooterTemplate>
</asp:Repeater>
</div>
</div>

My back-end code:

public partial class carousel : System.Web.UI.UserControl
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            var sublayout = Parent as Sublayout;
            var datasource = sublayout.DataSource;
            Item Carousel = Sitecore.Context.Database.GetItem(datasource);
            Item[] item = Carousel.Children.ToArray();
            rptCarousel.DataSource = item;
            rptCarousel.DataBind();
        }
    }

UPDATE CODE FROM COMMENT

Sitecore.Data.Fields.MultilistField multilistField = Sitecore.Context.Item.Fields["Select Item"]; 
if (multilistField != null && multilistField.TargetIDs.Any()) 
{
    foreach (ID id in multilistField.TargetIDs)
    {
        Item targetItem = Sitecore.Context.Database.Items[id];
        Item[] item = targetItem.Children.ToArray();
        rptCarousel.DataSource = item; 
        rptCarousel.DataBind(); 
    } 
}

Answer 1

Based on comments above, the first issue is that you have a MultiList but the code is not reading from it. Upon the update of the code from the comment section, please see below the updated one.

Problem

The updated code you've provided is not correct as it is initializing the array everytime as it is in the loop and also, you are performing a GetChildren() on the selected item, which is the carousel item itself.

Solution

Sitecore.Data.Fields.MultilistField multilistField = Sitecore.Context.Item.Fields["Select Item"];

if (multilistField != null && multilistField.TargetIDs.Any())
{
    var selectedItems = multilistField.GetItems();

    rptCarousel.DataSource = items;

    rptCarousel.DataBind();
}

If GetItems() method does not exist in your current Sitecore.Kernel, which should not be the case, you will need to amend the above code to the one below

Sitecore.Data.Fields.MultilistField multilistField = Sitecore.Context.Item.Fields["Select Item"];

if (multilistField != null && multilistField.TargetIDs.Any())
{
    ArrayList carouselArray = new ArrayList();

    foreach (ID targetId in multilistField.TargetIDs)
    {
        Item carouselItem = Sitecore.Context.Database.GetItem(targetId);
        if (carouselItem != null)
        {
            carouselArray.Add(carouselItem);
        }
    }

    rptCarousel.DataSource = carouselArray;

    rptCarousel.DataBind();
}

Note that you can create an extension for the MultiList field and adds the code that perform the retrieving of the selected items.