DynamicPlaceholder get Parameter Templates Treelistvalues

Question

I've created a Parameters Template with a Treelist Field and a Rendering which uses this Template. That works so far I can select multiple values. But Now I am using this rendering in a dynamic Placeholder and I want to get the Selected Values from my Parameter. The Only thing I get at the moment are Pipe separated GUIDs and I was hoping that I could use MultilistField to get the Values from my selection. But I don't know how to initialize the Multilistfield. Because the Guids I am currently getting with the following Function

public string GetParameter(DynamicPlaceholderRenderContext context, string parameter)
{
        var parameterValue = context.Parameters.ContainsKey(parameter) ? context.Parameters[parameter] :
             context.Rendering.Parameters.Contains(parameter) ? context.Rendering.Parameters[parameter] :
             string.Empty;

        return parameterValue;
 }

which I Call in my view inside the wrapper Method fpr my DynamicPlaceholder

 @Html.Sitecore().DynamicPlaceholder("grid-column", CreateWrapper)

 @functions
 {

     private readonly IParameterTemplatesProvider _parameterTemplatesService = new ParameterTemplatesProvider();

     HtmlString CreateWrapper(HtmlString htmlString, DynamicPlaceholderRenderContext context)
     { 
        var cssClasses = _parameterTemplatesService.GetParameter(context, Templates.GridBase.Fields.CssClassesFieldName);


     }
 }

When I try to get some "context" data like this

var test = Sitecore.Context.Item.Fields[Templates.Column.Fields.CssClassesFieldName];

I get null back but no Object or something else where I can create a MultilistField. I Think I've some prober missunderstandings when I can access

Sitecore.Context.Item or RenderingContext.Current.Rendering.Item how can get the Real Selected values from my Treelist

I am not shure if my problems are associated with DynamicPlaceholders or some other missunderstandings in the sitecore technology :-)

Answer 1

Rendering parameters are stored as name-value-collection (like a query string) with just the raw value - which for a multi-list field is a pipe-separated list of IDs.

You could change your GetParameter() method to something like the following, to get a list of items:

public IList<Item> GetParameter(DynamicPlaceholderRenderContext context, string parameter)
{
    var parameterValue = context.Parameters.ContainsKey(parameter) ? context.Parameters[parameter] :
            context.Rendering.Parameters.Contains(parameter) ? context.Rendering.Parameters[parameter] :
            string.Empty;

    // You might want to do some more checks here
    // - check for valid IDs, non-null items returned etc.
    return parameterValue.Split(new [] {'|'}, StringSplitOptions.RemoveEmptyEntries)
                         .Select(id => Sitecore.Context.Database.GetItem(id))
                         .ToList();
}

As noted you might want to do some error-checking just in case.