Rendering Partial view as a string inside SignalR Hub

Question

I am trying to dynamically load partial view contents in one of my views via a SignalR Hub to update client side data. For this I have to render the Partial view as a string in the SignalR Hub and send this string to the client side. I know how to render a partial view as a string inside a controller, but how would I do this outside of a controller?

Answer 1

I am trying to dynamically load partial view contents in one of my views via a SignalR Hub to update client side data. For this I have to render the Partial view as a string in the SignalR Hub and send this string to the client side.

If you'd like to render your view/partial view as a html string within your hub method, you can refer to this blog with example that demonstrates how to render a Partial View to string.

And I did a test with the example code RazorPartialToStringRenderer in my SignalR app, which work well for me.

private readonly IRazorPartialToStringRenderer _renderer;
public ChatHub(IRazorPartialToStringRenderer renderer)
{
    _renderer = renderer;
}
public async Task SendMessage(string user, string message)
{

    var view_result_mes = await _renderer.RenderPartialToStringAsync<string>("_SayHelloPartialView", null);

    //...

Code referenced from above blog

public interface IRazorPartialToStringRenderer
{
    Task<string> RenderPartialToStringAsync<TModel>(string partialName, TModel model);
}

public class RazorPartialToStringRenderer : IRazorPartialToStringRenderer
{
    private IRazorViewEngine _viewEngine;
    private ITempDataProvider _tempDataProvider;
    private IServiceProvider _serviceProvider;
    public RazorPartialToStringRenderer(
        IRazorViewEngine viewEngine,
        ITempDataProvider tempDataProvider,
        IServiceProvider serviceProvider)
    {
        _viewEngine = viewEngine;
        _tempDataProvider = tempDataProvider;
        _serviceProvider = serviceProvider;
    }
    public async Task<string> RenderPartialToStringAsync<TModel>(string partialName, TModel model)
    {
        var actionContext = GetActionContext();
        var partial = FindView(actionContext, partialName);
        using (var output = new StringWriter())
        {
            var viewContext = new ViewContext(
                actionContext,
                partial,
                new ViewDataDictionary<TModel>(
                    metadataProvider: new EmptyModelMetadataProvider(),
                    modelState: new ModelStateDictionary())
                {
                    Model = model
                },
                new TempDataDictionary(
                    actionContext.HttpContext,
                    _tempDataProvider),
                output,
                new HtmlHelperOptions()
            );
            await partial.RenderAsync(viewContext);
            return output.ToString();
        }
    }
    private IView FindView(ActionContext actionContext, string partialName)
    {
        var getPartialResult = _viewEngine.GetView(null, partialName, false);
        if (getPartialResult.Success)
        {
            return getPartialResult.View;
        }
        var findPartialResult = _viewEngine.FindView(actionContext, partialName, false);
        if (findPartialResult.Success)
        {
            return findPartialResult.View;
        }
        var searchedLocations = getPartialResult.SearchedLocations.Concat(findPartialResult.SearchedLocations);
        var errorMessage = string.Join(
            Environment.NewLine,
            new[] { $"Unable to find partial '{partialName}'. The following locations were searched:" }.Concat(searchedLocations)); ;
        throw new InvalidOperationException(errorMessage);
    }
    private ActionContext GetActionContext()
    {
        var httpContext = new DefaultHttpContext
        {
            RequestServices = _serviceProvider
        };
        return new ActionContext(httpContext, new RouteData(), new ActionDescriptor());
    }
}

Test Result