Saturday, October 29, 2011

ASP.NET MVC 3 - Representing contents in Razor View

The Razor view engine in ASP.NET MVC 3, throws error when we specify the content block directly without enclosing it in tags especially inside the coding constructs like if, for loop and so on.

Following Snippet throws error
@if(condition) {
    Any direct content.......

In such cases, developers usually specify tags like <span> as a workaround in order to specify the contents. But there exists two ways for directly represent this case.
  1. @: - for indicating the characters following it are content items and usually used for representing single line content.
  2. <text>....</text> - entire content block is enclosed within the <text>....</text> element and usually used for representing multi line contents.

@if(condition) {
    <text>Multi line statement 1
    Multi line statement 1
    Multi line statement n</text>

@if(condition) {
    @:single line content goes here....

This is a straight forward feature but unexposed to several developers. It is simple but effective.

Sunday, October 23, 2011

Parsing and Manipulating HTML strings - C#

Recently I came across a situation, where I need to retrieve an HTML string created and stored by an ASP application. Upon retrieving the html string, I need to parse the string and manipulate html string by removing some deprecated attributes and us some other equivalent alternate instead. For instance the size attribute in the font element need to be replaced with css font-size attribute.

Snippet 1:

<font size="1">......</font>


<font style="font-size: 9px;">......</font>

One additional thing we need to note here is, since we don't have any direct equivalent of the unit and value for the size attribute, I simply changed it to the expected size for the invoking applications.

Fine, now comes core of the issue about how to manipulate the HTML string. Initially I thought of using regex. Suddenly, I remembered of the nice tool Html Agility Pack which I explored few months back. Its an HTML parser that allows us to select an HTML element and manipulate it very easily. It uses the XPath to navigate through the elements. If you don't know XPath, no problem. You can refer to examples over the net (like in msdn and w3schools ) and find the XPath that suits better your requirement in less than a minute.

Following is the code for the situation I mentioned above.
Snippet 2:

private string RestructureDeprecatedAttributes(string htmlText)
    HtmlDocument document = new HtmlDocument();
    HtmlNodeCollection fontNodeCollection;
    fontNodeCollection = document.DocumentNode.SelectNodes("//font[@size]");

    if (fontNodeCollection != null)
        foreach (HtmlNode fontNode in fontNodeCollection)
            HtmlAttribute sizeAttribute = fontNode.Attributes["size"];

            if (!string.IsNullOrWhiteSpace(sizeAttribute.Value) && int.Parse(sizeAttribute.Value) > 0)
                if (sizeAttribute.Value.Equals("1"))
                    fontNode.SetAttributeValue("style", "font-size: 9px;");
                    fontNode.SetAttributeValue("style", "font-size: 11px;");

    return document.DocumentNode.WriteTo();

The selectors are really powerful which allows us to select the nodes that perfectly matches our criteria. The Html Agility Pack provides several methods that supports the manipulation of HTML strings in a very easy manner. You can infer this from the above code.

Sunday, October 9, 2011

ASP.NET MVC - Html.Partial vs Html.RenderPartial

RenderPartial writes the result directly to the response, technically speaking, directly into the calling object's TextWriter.

Partial on the other hand returns the HTML markup as string, which buffers the content. It achieves by creating and using a separate TextWriter.

Syntactic representation:
RenderPartial should be used inside a code block (obviously followed by a semicolon).


Partial can be used directly as it returns the HTML markup as string.


Considering the performance RenderPartial is a bit faster and hence developers prefer using it inside the looping constructs and related scenarios.

Preference of Partial prevails in the case of regular syntax usage(meaning - uniform syntax usage as we don't need to wrap inside the code block) and if we need to perform any manipulation with the resultant HTML markup string.
Creative Commons License
This work by Tito is licensed under a Creative Commons Attribution 3.0 Unported License.