k12 MVC approach custom checkbox list development

Can you give use an example of what you are trying to achieve? If you use a multiple choice form control and let say list of your check boxes:

if 2nd and 3nd checkboxes are selected your value will be 2|3, you can apply regex or for example if you want to have 1 least one checkbox selected, you can checked required checkbox and add validation rule that minimum text length is 1

In MVC, in order to get an array of values in a Form post, you need to have multiple controls with the same name. Example:

<input type="checkbox" name="MyCheckboxes" value="1"/>
<input type="checkbox" name="MyCheckboxes" value="2"/>
<input type="checkbox" name="MyCheckboxes" value="3"/>
<input type="checkbox" name="MyCheckboxes" value="4"/>

This will then work for catching int[] MyCheckboxes In the binding.

In your rendering of the Model's EditorFor, you may have to manually do it with a foreach loop through the available options (and which are already checked), but as long as you follow that naming schema, it should work. I ran into the same thing myself, although i haven't created a Form Component for this.