Custom BaseTemplate for ActionMailer.Standalone

RazorTemplateBase

public class RazorTemplateBase<T> : TemplateBase<T>
{
    private StandaloneHtmlHelpers _html;
    public StandaloneHtmlHelpers Html
    {
        get
        {
            _html = _html ?? new StandaloneHtmlHelpers(TemplateService, ViewBag);
            return _html;
        }
    }
}

public class StandaloneHtmlHelpers
{
    public StandaloneHtmlHelpers()
    {
        _executeContext = new ExecuteContext();
        _templateService = new TemplateService();
    }

    public StandaloneHtmlHelpers(ITemplateService templateService = null, DynamicViewBag viewBag = null)
    {
        _executeContext = (viewBag == null) ? new ExecuteContext() : new ExecuteContext(viewBag);
        _templateService = templateService ?? new TemplateService();
    }

    private readonly ExecuteContext _executeContext;
    private readonly ITemplateService _templateService;

    public IEncodedString Raw(string input)
    {
        return new RawString(input);
    }

    public TemplateWriter Partial(string templateName, object model = null)
    {
        var template = _templateService.Resolve(templateName, model);
        if(template == null)
            throw new ArgumentException("No template could be resolved with the name '" + templateName + "'");

        return new TemplateWriter(tw => tw.Write(template.Run(_executeContext)));
    }
}