liveBook · Manning

TagHelperOutput

As explained in Pro ASP.NET Core 7, Tenth Edition

TagHelperOutput is an ASP.NET Core object that represents and exposes the element and content produced during tag-helper processing.

TagHelperOutput represents the HTML element produced during tag-helper processing. A tag helper receives it in Process, then changes the element, attributes, content, or surrounding markup before Razor renders the view. section 25.2.1

Use TagHelperOutput to control these parts of the rendered result:

  • Set TagName to change the output element’s tag name. section 25.2.1
  • Use Attributes to add or modify attributes, such as applying Bootstrap classes to a tr element. section 25.2.1
  • Use Content to replace or define the element’s content, and GetChildContentAsync() to access the original content. section 25.2.1
  • Use PreElement and PostElement to insert markup outside the target element, or PreContent and PostContent to surround its existing content. section 25.3.3

Applying output attributes

A tag helper can transform configured attributes into output markup. In TrTagHelper, output.Attributes.SetAttribute("class", $"bg-{BgColor} text-center text-{TextColor}") replaces or sets the class attribute, producing Bootstrap styling such as bg-dark text-center text-white. section 25.2.1

Adding content around an element

A wrapper tag helper appends a div before and after an element with wrap="true" through output.PreElement.AppendHtml(elem) and output.PostElement.AppendHtml(elem). A highlighting tag helper instead places <b><i> before the existing content and </i></b> afterward through PreContent and PostContent. section 25.3.3

Table 25.4 The TagHelperOutput properties and methods (view table figure)

Name

Description

TagName

This property is used to get or set the tag name for the output element.

Attributes

This property returns a dictionary containing the attributes for the output element.

Content

This property returns a TagHelperContent object that is used to set the content of the element.

GetChildContentAsync()

This asynchronous method provides access to the content of the element that will be transformed, as demonstrated in the “Creating Shorthand Elements” section.

PreElement

This property returns a TagHelperContext object that is used to insert content in the view before the output element. See the “Prepending and Appending Content and Elements” section.

PostElement

This property returns a TagHelperContext object that is used to insert content in the view after the output element. See the “Prepending and Appending Content and Elements” section.

PreContent

This property returns a TagHelperContext object that is used to insert content before the output element’s content. See the “Prepending and Appending Content and Elements” section.

PostContent

This property returns a TagHelperContext object that is used to insert content after the output element’s content. See the “Prepending and Appending Content and Elements” section.

TagMode

This property specifies how the output element will be written, using a value from the TagMode enumeration. See the “Creating Shorthand Elements” section.

SupressOuput()

Calling this method excludes an element from the view. See the “Suppressing the Output Element” section.

Browse the output API reference for TagName, Attributes, Content, GetChildContentAsync(), and surrounding-element properties. section 25.2.1

How Pro ASP.NET Core 7, Tenth Edition covers it

How deep it goes
Explains the main properties and demonstrates attribute, wrapper, and content transformations, without descending into rendering internals.
Examples
Uses Bootstrap row classes, a div wrapper, and bold italic highlighting to demonstrate output modification.
What it assumes
Assumes familiarity with ASP.NET Core tag-helper classes, Process methods, Razor views, and HTML attributes.
What you can do after
Apply it in a TagHelper Process method to modify elements, attributes, content, or markup surrounding rendered elements.
How it connects
Connects TagHelperOutput with tag helpers, TagHelperContext, TagHelperContent, Razor views, and HTML attributes.
Cover of Pro ASP.NET Core 7, Tenth Edition
liveBookmanning.com
Read Pro ASP.NET Core 7, Tenth Edition on liveBook Get the book at manning.com

Also explained in

Compare how 2 books explain TagHelperOutput →

Related concepts

This explainer was generated by Manning's knowledge graph from the text of Pro ASP.NET Core 7, Tenth Edition. The section links point to the parts of the book it draws on.