Convert IHtmlContent/TagBuilder to string in C#

Question

I am using ASP.NET 5. I need to convert IHtmlContent to String

IIHtmlContent is part of the ASP.NET 5 Microsoft.AspNet.Html.Abstractions namespace and is an interface that TagBuilder implements

Simplified I have the following method

public static IHtmlContent GetContent()
{
    return new HtmlString("<tag>blah</tag>");
}

When I reference it

string output = GetContent().ToString();

I get the following output for GetContent()

"Microsoft.AspNet.Mvc.Rendering.TagBuilder"

and not

<tag>blah</tag>

which I want

I also tried using StringBuilder

StringBuilder html = new StringBuilder();
html.Append(GetContent());

but it also appends the same namespace and not the string value

I tried to cast it to TagBuilder

TagBuilder content = (TagBuilder)GetContent();

but TagBuilder doesn't have a method that converts to string

How do I convert IHtmlContent or TagBuilder to a string?

What about ToHtmlString? Also, where do you get IHtmlContent from? — shree.pat18
– shree.pat18, Commented Nov 12, 2015 at 9:34
I was referring to HtmlString class's method. Can you point me to the documentation for IHtmlContent? It doesn't seem to be on MSDN — shree.pat18
– shree.pat18, Commented Nov 12, 2015 at 10:00
It's seven years ago, but maybe it's usefull for someone anymore. If you call GetContent() from your html source code file (e.g.: in your cshtml: @Model.GetContent()) then in your browser app you'll see: blah. Therefor contains the question also a piece of an answer. — peter70
– peter70, Commented Dec 16, 2022 at 10:55

cygnim · Accepted Answer · 2019-03-05 21:07:11Z

67

If all you need to do is output the contents as a string, just add this method and pass your IHtmlContent object as a parameter to get the string output:

public static string GetString(IHtmlContent content)
{
    using (var writer = new System.IO.StringWriter())
    {        
        content.WriteTo(writer, HtmlEncoder.Default);
        return writer.ToString();
    } 
}

edited Mar 5, 2019 at 21:07

answered Nov 12, 2015 at 19:45

cygnim

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6 Comments

zoaz Over a year ago

Good answer.. This is what I was looking for.

NucS Over a year ago

Does not work on asp.vnext core. use HtmlEncoder.Default instead

bradlis7 Over a year ago

Shouldn't the StringWriter be wrapped in a using block?

cygnim Over a year ago

@bradlis7 you are correct. I have updated the solution to reflect your suggestion.

androbin Over a year ago

With Razor in Core you can simply use @tagBuilderInstance. It will build and write the result.

|

devfric · Accepted Answer · 2016-07-21 14:48:26Z

28

Adding to the answer above:

The new instance of the HtmlEncoder doesn't work in ASP.NET Core RTM as the Microsoft.Extensions.WebEncoders namespace was removed and the new HtmlEncoder class is moved to a new namespace System.Text.Encodings.Web, but this class is now written as an abstract and sealed class so you can't create a new instance or a derived class from it.

Pass HtmlEncoder.Default to the method and it will work

public static string GetString(IHtmlContent content)
{
    var writer = new System.IO.StringWriter();
    content.WriteTo(writer, HtmlEncoder.Default);
    return writer.ToString();
}

answered Jul 21, 2016 at 14:48

devfric

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Comments

vulcan raven · Accepted Answer · 2019-03-15 04:32:39Z

23

ASP.NET Core actually introduced handful of careful optimizations. If you are building an HTML extension method, then the most efficient way is to avoid string:

public static IHtmlContent GetContent(this IHtmlHelper helper)
{
    var content = new HtmlContentBuilder()
                     .AppendHtml("<ol class='content-body'><li>")
                     .AppendHtml(helper.ActionLink("Home", "Index", "Home"))
                     .AppendHtml("</li>");

    if(SomeCondition())
    {
        content.AppendHtml(@"<div>
            Note `HtmlContentBuilder.AppendHtml()` is Mutable
            as well as Fluent/Chainable.
        </div>");
    }

    return content;
}

~~Finally in the razor view, we don't even need @Html.Raw(Html.GetContent()) anymore (which used to be required in ASP.NET MVC 5)~~ - not valid based on Lukáš Kmoch comment below: ASP.NET MVC 5 has type MvcHtmlString. You don't need to use Html.Raw()

just calling @Html.GetContent() is sufficient and Razor will take care of all the escaping business.

edited Mar 15, 2019 at 4:32

answered Mar 1, 2017 at 0:25

vulcan raven

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2 Comments

Hunter Nelson Over a year ago

The reason I liked the server side rendering is that it was so much faster to code boring markup at the expense of performance. Why are we injecting an ordered list into markup so we can render and anchor tag? This has to be bad for SEO, and increase development time. Arrrgh

Lukáš Kmoch Over a year ago

ASP.NET MVC 5 has type MvcHtmlString. You don't need to use Html.Raw()

Tom · Accepted Answer · 2021-11-18 16:21:01Z

2

Here's an extension method so you can use it like ToString().

    public static string ToHtmlString(this IHtmlContent content)
    {
        if (content is HtmlString htmlString)
        {
            return htmlString.Value;
        }

        using (var writer = new StringWriter())
        {
            content.WriteTo(writer, HtmlEncoder.Default);
            return writer.ToString();
        }
    }

answered Nov 18, 2021 at 16:21

Tom

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Comments

workingbird · Accepted Answer · 2019-01-03 06:38:39Z

0

there is a sample: https://github.com/aspnet/Mvc/blob/release/2.2/test/Microsoft.AspNetCore.Mvc.Views.TestCommon/HtmlContentUtilities.cs

public static string HtmlContentToString(IHtmlContent content, HtmlEncoder encoder = null)
        {
            if (encoder == null)
            {
                encoder = new HtmlTestEncoder();
            }

            using (var writer = new StringWriter())
            {
                content.WriteTo(writer, encoder);
                return writer.ToString();
            }
        }

answered Jan 3, 2019 at 6:38

workingbird

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