I am trying to adopt SPA (react) + umbraco solution described here: https://github.com/systempioneer/React-Umbraco-Example/blob/master/UmbracoReactStarterKit/Controllers/ReactRoutesController.cs to Umbraco 8.

The default controller is a controller of type RenderMvcController which expects a model of type ContentModel (former RenderModel in umbraco v7).

The problem is that the supplied model when converting model to string is PublishedContentModel which is the auto-generated model by ModelsBuilder.

I had to make a few changes to adopt the source code to Umbraco 8 but the resulting values are of the same type like in the base solution above.

The ContentModel that needs to be returned to the view:

public class MasterModel : ContentModel
{
    public MasterModel(IPublishedContent content) : base(content)
    {
    }

    public InitialState InitialState { get; set; }
}

This is my controller:

public class ReactRoutesController : ReactRenderMvcController
{
    public override ActionResult Index(ContentModel model)
    {
        return View("Master", CreateMasterModel());
    }

    private MasterModel CreateMasterModel()
    {
        var home = Umbraco.ContentAtRoot().First();
        var viewResult = ViewFromContentId(CurrentPage.Id); // returns view with model of type PublishedContentModel
        var viewResultAsString = viewResult.RenderToString(); // this calls RenderToString() shown below
        var model = new MasterModel(CurrentPage)
        {
            InitialState = new InitialState
            {
                content = GetContentPages(),
                homeUrl = home.Url,
                location = Request.Url.AbsolutePath,
                currentContent = new InitialState.CurrentContent
                {
                    Name = CurrentPage.Name,
                    Url = Request.Url.AbsolutePath,
                    Content = viewResultAsString
                },
                currentPageName = CurrentPage.Name
            }
        };

        return model;
    }
}

inheriting from:

public class ReactRenderMvcController : RenderMvcController
{
    public ViewResult ViewFromContentId(int id)
    {
        var result = Umbraco.ContentQuery.Content(id); // gets the current document type with doc type model
        var renderModel = ViewExtensions.CreateRenderModel(result, RouteData).Content;

        return View(renderModel.GetTemplateAlias(), renderModel);
    }

}

The extension which is supposed to render the string from the view:

public static class ViewExtensions
{
    // https://stackoverflow.com/a/19208941
    public static string RenderToString(this ViewResult partialView)
    {
        var httpContext = HttpContext.Current;

        if (httpContext == null)
        {
            throw new NotSupportedException("An HTTP context is required to render the partial view to a string");
        }

        var controllerName = httpContext.Request.RequestContext.RouteData.Values["controller"].ToString();

        var controller = (ControllerBase)ControllerBuilder.Current.GetControllerFactory().CreateController(httpContext.Request.RequestContext, controllerName);

        var controllerContext = new ControllerContext(httpContext.Request.RequestContext, controller);

        var view = ViewEngines.Engines.FindPartialView(controllerContext, partialView.ViewName).View;

        var sb = new StringBuilder();

        using (var sw = new StringWriter(sb))
        {
            using (var tw = new HtmlTextWriter(sw))
            {
                var viewContext = new ViewContext(controllerContext, view, partialView.ViewData, partialView.TempData, tw);
                view.Render(viewContext, tw); // <---- THIS IS WHERE THE ERROR OCCURS - I guess it's because the controller expects `ContentModel` while it is being supplied `PublishedContentModel` instead - partialView parameter has model of type `PublishedContentModel`
            }
        }

        return sb.ToString();
    }

The actual error says:

Cannot bind source type Umbraco.Web.PublishedModels.Home to model type MyDomain.Models.MasterModel. The source is a ModelsBuilder type, but the view model is not.

To be honest I don't know how this could work on the original version the solution is made for ( v.7.6.2). I tried to install it but getting an error on db installation and not able to run it. umbraco's RenderMvcController always expected RenderModel, not a PublishedContentModel.