Question

I was looking at the example here:

http://tinyurl.com/au3vydl

This example uses a helper to display a google graph image using razor:

@Html.DrawChart("p", "40,60,40", "250x100", "Pie Chart")

This method assembles the correct code to return the chart:

<img src='http://chart.apis.google.com/chart?chs=250x100&amp;chd=t:40,60,40&amp;cht=p&amp;chl=Pie Chart' />

However in the browser this displays as html code, not the actual image. If I copy the exact same code that the helper outputs into the view, it displays fine. Is there anything needed to change the output of the @Html.Helper to code instead of a literal string?

Helper code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Text;
using System.Web.Mvc;

namespace SolarCars.Helpers
{
    public static class GoogleChart
    {
        /// <summary>
        /// Draws the chart.
        /// </summary>
        /// <param name="helper">The helper.</param>
        /// <param name="chartType">Type of the chart.</param>
        /// <param name="chartData">The chart data.</param>
        /// <param name="chartSize">Size of the chart.</param>
        /// <param name="chartLabel">The chart label.</param>
        /// <returns></returns>
        public static string DrawChart(this HtmlHelper helper, string chartType, string chartData, string chartSize, string chartLabel)
        {
            StringBuilder chartHtml = new StringBuilder("<img src='http://chart.apis.google.com/chart?chs=");
            chartHtml.Append(chartSize);
            chartHtml.Append("&amp;chd=t:");
            chartHtml.Append(chartData);
            chartHtml.Append("&amp;cht=");
            chartHtml.Append(chartType);
            chartHtml.Append("&amp;chl=");
            chartHtml.Append(chartLabel);
            chartHtml.Append("' />");

            return chartHtml.ToString();
        }
    }
}

Answer 1

If you return strings in an @ or <%: block the result will be automatically escaped. This was a (I think) a change between MVC1 and MVC2. The solution to this is to have your helper method return an instance of IHtmlString.

public static IHtmlString DrawChart(...)

Then switch your return to return a new HtmlString

return new HtmlString(chartHtml.ToString());