Replace line break characters with <br /> in ASP.NET MVC Razor view

Use the CSS white-space property instead of opening yourself up to XSS vulnerabilities!

<span style="white-space: pre-line">@Model.CommentText</span>

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Try the following:

@MvcHtmlString.Create(Model.CommentText.Replace(Environment.NewLine, "<br />"))

Update:

According to marcind's comment on this related question, the ASP.NET MVC team is looking to implement something similar to the <%: and <%= for the Razor view engine.

Update 2:

We can turn any question about HTML encoding into a discussion on harmful user inputs, but enough of that already exists.

Anyway, take care of potential harmful user input.

@MvcHtmlString.Create(Html.Encode(Model.CommentText).Replace(Environment.NewLine, "<br />"))

Update 3 (Asp.Net MVC 3):

@Html.Raw(Html.Encode(Model.CommentText).Replace("\n", "<br />"))

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Split on newlines (environment agnostic) and print regularly -- no need to worry about encoding or xss:

@if (!string.IsNullOrWhiteSpace(text)) 
{
    var lines = text.Split(new[] { '\r', '\n' }, StringSplitOptions.RemoveEmptyEntries);
    foreach (var line in lines)
    {
        <p>@line</p>
    }
}

(remove empty entries is optional)

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Omar's third solution as an HTML Helper would be:

public static IHtmlString FormatNewLines(this HtmlHelper helper, string input)
{
    return helper.Raw(helper.Encode(input).Replace("\n", "<br />"));
}

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Applying the DRY principle to Omar's solution, here's an HTML Helper extension:

using System.Web.Mvc;
using System.Text.RegularExpressions;

namespace System.Web.Mvc.Html {
    public static class MyHtmlHelpers {
        public static MvcHtmlString EncodedReplace(this HtmlHelper helper, string input, string pattern, string replacement) {
            return new MvcHtmlString(Regex.Replace(helper.Encode(input), pattern, replacement));
        }
    }
}

Usage (with improved regex):

@Html.EncodedReplace(Model.CommentText, "[\n\r]+", "<br />")

This also has the added benefit of putting less onus on the Razor View developer to ensure security from XSS vulnerabilities.

My concern with Jacob's solution is that rendering the line breaks with CSS breaks the HTML semantics.

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I needed to break some text into paragraphs ("p" tags), so I created a simple helper using some of the recommendations in previous answers (thank you guys).

public static MvcHtmlString ToParagraphs(this HtmlHelper html, string value) 
    { 
        value = html.Encode(value).Replace("\r", String.Empty);
        var arr = value.Split('\n').Where(a => a.Trim() != string.Empty);
        var htmlStr = "<p>" + String.Join("</p><p>", arr) + "</p>";
        return MvcHtmlString.Create(htmlStr);
    }

Usage:

@Html.ToParagraphs(Model.Comments)

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I prefer this method as it doesn't require manually emitting markup. I use this because I'm rendering Razor Pages to strings and sending them out via email, which is an environment where the white-space styling won't always work.

public static IHtmlContent RenderNewlines<TModel>(this IHtmlHelper<TModel> html, string content)
{
    if (string.IsNullOrEmpty(content) || html is null)
    {
        return null;
    }

    TagBuilder brTag = new TagBuilder("br");
    IHtmlContent br = brTag.RenderSelfClosingTag();
    HtmlContentBuilder htmlContent = new HtmlContentBuilder();

    // JAS: On the off chance a browser is using LF instead of CRLF we strip out CR before splitting on LF.
    string lfContent = content.Replace("\r", string.Empty, StringComparison.InvariantCulture);
    string[] lines = lfContent.Split('\n', StringSplitOptions.None);
    foreach(string line in lines)
    {
        _ = htmlContent.Append(line);
        _ = htmlContent.AppendHtml(br);
    }

    return htmlContent;
}

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