Calling a Partial View of Nop.Web from Plugin Custom View Engine

One of the nice feature of the .NetCore framework is its pluggability. This means you can completely replace the default view engine(s) with a custom one.

One of the reason for using a custom view engine is to change the default views location and sometimes you need to change the views location at run-time. To do this you can extend the default view engine(s) and then change the default views location variables at run-time. 

Here is an example when the default Checkout Views are replaced with Partial Views loaded from a Payment Plugin 

using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.AspNetCore.Mvc.Razor;

using Nop.Core;
using Nop.Core.Data;
using Nop.Core.Infrastructure;
using Nop.Services.Plugins;
using Nop.Services.Configuration;

using Nop.Web.Framework.Themes;

namespace Nop.Plugin.Pluign.Name.ViewEngine
{
    public class CustomViewEngine : IViewLocationExpander
    {

        public string storeTheme = "DefaultClean";

        public void PopulateValues(ViewLocationExpanderContext context)
        {
            if (context.AreaName?.Equals("Admin") ?? false)
                return;

            var settingService = EngineContext.Current.Resolve<ISettingService>();
            var storeContext = EngineContext.Current.Resolve<IStoreContext>();

            storeTheme = settingService.GetSettingByKey("storeinformationsettings.defaultstoretheme", "DefaultClean", storeContext.CurrentStore.Id, true);

            var themeContext = (IThemeContext)context.ActionContext.HttpContext.RequestServices.GetService(typeof(IThemeContext));
            context.Values[storeTheme] = themeContext.WorkingThemeName;
        }

        public IEnumerable<string> ExpandViewLocations(ViewLocationExpanderContext context, IEnumerable<string> viewLocations)
        {

            //Confirm database is installed
            if (DataSettingsManager.DatabaseIsInstalled)
            {
                var pluginService = EngineContext.Current.Resolve<IPluginService>();

                var plugin = pluginService.GetPluginDescriptorBySystemName<IPlugin>("Plugin.Name", LoadPluginsMode.InstalledOnly);
                if (plugin != null)
                {
                    if (plugin.SystemName == "Plugin.Name")
                    {
                        if (context.AreaName == "Admin")
                        {

                        }
                        else
                        {
                            if (!context.Values.TryGetValue(storeTheme, out string theme))
                                return viewLocations;
                            if (context.ControllerName == "RealOnePageCheckout" && context.ViewName == "RealOnePageCheckout")
                            {
                                viewLocations = new[] { $"~/Plugins/Plugin.Name/Views/FrontView/RealOnePageCheckout.cshtml" }.Concat(viewLocations);
                            }
                            else if (context.ControllerName == "Checkout" && context.ViewName == "BillingAddress")
                            {
                                viewLocations = new[] { $"~/Plugins/Plugin.Name/Views/FrontView/BillingAddress.cshtml" }.Concat(viewLocations);
                            }
                            else if (context.ControllerName == "Checkout" && context.ViewName == "ShippingMethod")
                            {
                                viewLocations = new[] { $"~/Plugins/Plugin.Name/Views/FrontView/ShippingMethod.cshtml" }.Concat(viewLocations);
                            }
                            else if (context.ControllerName == "Checkout" && context.ViewName == "OpcShippingMethods")
                            {
                                viewLocations = new[] { $"~/Plugins/Plugin.Name/Views/FrontView/OpcShippingMethods.cshtml" }.Concat(viewLocations);
                            }
                            else if (context.ControllerName == "Checkout" && context.ViewName == "Completed")
                            {
                                viewLocations = new[] { $"~/Plugins/Plugin.Name/Views/FrontView/Completed.cshtml" }.Concat(viewLocations);
                            }
                        }
                    }
                }
            }

            return viewLocations;
        }
    }
}