ViewRenderer.cs

/// <summary>
/// Class that renders MVC views to a string using the standard MVC View Engine to render the view. 
/// </summary>
public class ViewRenderer
{
    /// <summary>
    /// Required Controller Context
    /// </summary>
    protected ControllerContext Context { get; set; }

    /// <summary>
    /// Initializes the ViewRenderer with a Context.
    /// </summary>
    /// <param name="controllerContext">
    /// If you are running within the context of an ASP.NET MVC request pass in
    /// the controller's context. 
    /// Only leave out the context if no context is otherwise available.
    /// </param>
    public ViewRenderer(ControllerContext controllerContext = null)
    {
        // Create a known controller from HttpContext if no context is passed
        if (controllerContext == null) {
            if (HttpContext.Current != null)
                controllerContext = CreateController<ErrorController>().ControllerContext;
            else
                throw new InvalidOperationException(
                    "ViewRenderer must run in the context of an ASP.NET " +
                    "Application and requires HttpContext.Current to be present.");
        }
        Context = controllerContext;
    }

    /// <summary>
    /// Renders a full MVC view to a string. Will render with the full MVC
    /// View engine including running _ViewStart and merging into _Layout        
    /// </summary>
    /// <param name="viewPath">
    /// The path to the view to render. Either in same controller, shared by 
    /// name or as fully qualified ~/ path including extension
    /// </param>
    /// <param name="model">The model to render the view with</param>
    /// <returns>String of the rendered view or null on error</returns>
    public string RenderView(string viewPath, object model)
    {
        return RenderViewToStringInternal(viewPath, model, false);
    }


    /// <summary>
    /// Renders a partial MVC view to string. Use this method to render
    /// a partial view that doesn't merge with _Layout and doesn't fire
    /// _ViewStart.
    /// </summary>
    /// <param name="viewPath">
    /// The path to the view to render. Either in same controller, shared by 
    /// name or as fully qualified ~/ path including extension
    /// </param>
    /// <param name="model">The model to pass to the viewRenderer</param>
    /// <returns>String of the rendered view or null on error</returns>
    public string RenderPartialView(string viewPath, object model)
    {
        return RenderViewToStringInternal(viewPath, model, true);
    }

    /// <summary>
    /// Renders a partial MVC view to string. Use this method to render
    /// a partial view that doesn't merge with _Layout and doesn't fire
    /// _ViewStart.
    /// </summary>
    /// <param name="viewPath">
    /// The path to the view to render. Either in same controller, shared by 
    /// name or as fully qualified ~/ path including extension
    /// </param>
    /// <param name="model">The model to pass to the viewRenderer</param>
    /// <param name="controllerContext">Active Controller context</param>
    /// <returns>String of the rendered view or null on error</returns>
    public static string RenderView(string viewPath, object model, ControllerContext controllerContext)
    {
        ViewRenderer renderer = new ViewRenderer(controllerContext);
        return renderer.RenderView(viewPath, model);
    }

    /// <summary>
    /// Renders a partial MVC view to string. Use this method to render
    /// a partial view that doesn't merge with _Layout and doesn't fire
    /// _ViewStart.
    /// </summary>
    /// <param name="viewPath">
    /// The path to the view to render. Either in same controller, shared by 
    /// name or as fully qualified ~/ path including extension
    /// </param>
    /// <param name="model">The model to pass to the viewRenderer</param>
    /// <param name="controllerContext">Active Controller context</param>
    /// <param name="errorMessage">optional out parameter that captures an error message instead of throwing</param>
    /// <returns>String of the rendered view or null on error</returns>
    public static string RenderView(string viewPath, object model, ControllerContext controllerContext, out string errorMessage)
    {
        errorMessage = null;
        try {
            ViewRenderer renderer = new ViewRenderer(controllerContext);
            return renderer.RenderView(viewPath, model);
        } catch (Exception ex) {
            errorMessage = ex.GetBaseException().Message;
        }
        return null;
    }

    /// <summary>
    /// Renders a partial MVC view to string. Use this method to render
    /// a partial view that doesn't merge with _Layout and doesn't fire
    /// _ViewStart.
    /// </summary>
    /// <param name="viewPath">
    /// The path to the view to render. Either in same controller, shared by 
    /// name or as fully qualified ~/ path including extension
    /// </param>
    /// <param name="model">The model to pass to the viewRenderer</param>
    /// <param name="controllerContext">Active controller context</param>
    /// <returns>String of the rendered view or null on error</returns>
    public static string RenderPartialView(string viewPath, object model,
                                            ControllerContext controllerContext)
    {
        ViewRenderer renderer = new ViewRenderer(controllerContext);
        return renderer.RenderPartialView(viewPath, model);
    }

    /// <summary>
    /// Renders a partial MVC view to string. Use this method to render
    /// a partial view that doesn't merge with _Layout and doesn't fire
    /// _ViewStart.
    /// </summary>
    /// <param name="viewPath">
    /// The path to the view to render. Either in same controller, shared by 
    /// name or as fully qualified ~/ path including extension
    /// </param>
    /// <param name="model">The model to pass to the viewRenderer</param>
    /// <param name="controllerContext">Active controller context</param>
    /// <param name="errorMessage">optional output parameter to receive an error message on failure</param>
    /// <returns>String of the rendered view or null on error</returns>
    public static string RenderPartialView(string viewPath, object model, ControllerContext controllerContext, out string errorMessage)
    {
        errorMessage = null;
        try {
            ViewRenderer renderer = new ViewRenderer(controllerContext);
            return renderer.RenderPartialView(viewPath, model);
        } catch (Exception ex) {
            errorMessage = ex.GetBaseException().Message;
        }
        return null;
    }

    /// <summary>
    /// Internal method that handles rendering of either partial or full views.
    /// </summary>
    /// <param name="viewPath">
    /// The path to the view to render. Either in same controller, shared by 
    /// name or as fully qualified ~/ path including extension
    /// </param>
    /// <param name="model">Model to render the view with</param>
    /// <param name="partial">Determines whether to render a full or partial view</param>
    /// <returns>String of the rendered view</returns>
    protected string RenderViewToStringInternal(string viewPath, object model,
                                                bool partial = false)
    {
        // first find the ViewEngine for this view
        ViewEngineResult viewEngineResult = null;
        if (partial)
            viewEngineResult = ViewEngines.Engines.FindPartialView(Context, viewPath);
        else
            viewEngineResult = ViewEngines.Engines.FindView(Context, viewPath, null);

        if (viewEngineResult == null)
            throw new FileNotFoundException($"The requested view {viewPath} could not be found.");

        // get the view and attach the model to view data
        var view = viewEngineResult.View;
        Context.Controller.ViewData.Model = model;

        string result = null;

        using (var sw = new StringWriter()) {
            var ctx = new ViewContext(
                Context, 
                view,
                Context.Controller.ViewData,
                Context.Controller.TempData,
                sw);
            view.Render(ctx, sw);
            result = sw.ToString();
        }

        return result;
    }


    /// <summary>
    /// Creates an instance of an MVC controller from scratch 
    /// when no existing ControllerContext is present       
    /// </summary>
    /// <typeparam name="T">Type of the controller to create</typeparam>
    /// <returns></returns>
    public static T CreateController<T>(RouteData routeData = null)
        where T : System.Web.Mvc.Controller
    {
        //
        // An exception will be thrown if T cannot be resolved.
        //
        T controller = (T) DependencyResolver.Current.GetService(typeof(T));

        HttpContextBase wrapper = null;
        if (HttpContext.Current != null)
            wrapper = new HttpContextWrapper(HttpContext.Current);

        if (routeData == null)
            routeData = new RouteData();

        if (!routeData.Values.ContainsKey("controller") && !routeData.Values.ContainsKey("Controller"))
            routeData.Values.Add("controller", controller.GetType()
                .Name
                .ToLower()
                .Replace("controller", ""));

        controller.ControllerContext = new ControllerContext(wrapper, routeData, controller);
        return controller;
    }
}