Custom Widget Configuration Property

IPropertyTemplate is the new interface for defining custom widget configuration properties

https://community.telligent.com/community/11/w/api-documentation/64400/ipropertytemplate-plugin-type

What goes in the render method?  HTML and Javascript?...kind of what I'd put in a .vm file if I was to do it this way:
<property labelText="Select a Resource" id="message" dataType="string" template="searchSelection.vm" />

You can directly write Html/JavaScript to the writer that is passed into the render method or you could also implement IScriptablePlugin to define a widget and pass the writer into the widgetController.RenderContent.

We do also support local templates for custom configuration properties.  There is an example of that here:  https://community.telligent.com/community/11/w/developer-training/67226/embedding-a-custom-user-interface-for-a-configuration-property.  The process is similar, you are just defining the code in a vm file for local templates vs.  outputing the html/css from the render method a IPropertyTemplate class.

Thanks.  I did get the .vm method to work, but I'm going to probably be using this on a handful of widgets.  If I go the iPropertyTemplate route, do I just define the data type as "string" and then the controlType="class, dll" ??

dataType is dependent on your custom property.  instead of controlType use template="templatename" 

Ok... so TemplateName as defined in the plugin should be some sort of unique key identifier?

yes

Just rendering a plain textbox now  I'll debug and follow-up.

Doesn't look like the plugin is firing.  I deployed it and enabled.  Here is my code and how I'm referencing it in a widget.  If I use the same stuff in a .vm file it works.

<property labelText="Select a Resource" id="message" dataType="string" template="SearchableContentControl" />

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Telligent.Evolution.Extensibility.Configuration.Version1;

namespace HearingFirst.Plugins.Controls.PropertyControls
{
    public class SearchSelectionControl : IPropertyTemplate
    {
        public string[] DataTypes {

            get
            { 
                string[] d = new string[1] { "string" };
                return d;
            }
        }

        public string TemplateName => "SearchableContentControl";

        public bool SupportsReadOnly => false;

        public PropertyTemplateOption[] Options
        {
            get
            {
                return new PropertyTemplateOption[0];
            }
        }

        public string Name => "Hearing First - Searchable Content Widget Configuration Control";

        public string Description => "Provides functionality for selectable content control in widget configurations";

        public void Initialize()
        {

        }

        public void Render(TextWriter writer, IPropertyTemplateOptions options)
        {
            string defaultOption = "<option value=\"test\" >Search</option>";
            if (options.Value != null)
            {
                defaultOption = "<option value=\"placeholder\" >"+options.Value.ToString() + " </option>";
            }

            string script = String.Format(@"<select class=""form-control"" id=""{1}"" name=""$id"" style=""width: 100 % "">
                {3}
            </select>

            <script type=""text/javascript"">
            $(function() {
    
                jQuery('#${0}').select2({
                      ajax: {
                        url: ""$core_v2_widget.GetExecutedFileUrl('searchcallback.vm')"",
                        dataType: 'json',
                        placeholder: 'Search for an item',
                        minimumInputLength: 3,
            
                        // Additional AJAX parameters go here; see the end of this chapter for the full code of this example
                      }
                });
    
                var api = $context_v2_propertyTemplate.JsonApi;
     
                api.register({
                   hasValue: function() { 
                       return true;
                   },
                   val: function(val) {
                       return jQuery(""#{2}"").val();
                   }
                });

            });
            </script>", options.UniqueId.ToString(), options.UniqueId.ToString(), options.UniqueId.ToString(), defaultOption);

            writer.Write(script);
        }
    }
}

Velocity is not going to process, so all that code needs to be redone.  Your ajax callback would need to be to a rest endpoint or you could implement IHttpCallback as well and have it call back to this class.  I will take a look in the morning and see if we have a good straightforward example.