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17. Tag Helpers

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Tag Helpers

Tag helpers are the classes that can be invoked as an html tag or html attribute.

They generate a html tag or adds values into attributes of existing html tags.

Tag Helpers for ,

  • asp-controller
  • asp-action
  • asp-route-x
  • asp-route
  • asp-area

Tag Helpers for ,
  • asp-for

Tag Helpers for ,

Route URLs’ will be re-generated for and tags;

It generates the url as “controller/action” pattern.

Tag Helpers for

  • asp-append-version

Tag Helpers for

  • asp-validation-for

Tag Helpers for
  • asp-fallback-src
  • asp-fallback-test

Tag Helpers for

  • asp-validation-summary

Tag Helpers for

will be converted as:

asp-controller and asp-action

Generates route url for the specified action method with “controller/action” route pattern.

Tag Helpers for

will be converted as:

asp-controller and asp-action

Generates route url for the specified action method with “controller/action” route pattern.

Tag Helpers for and

will be converted as:

asp-route-x

Specifies value for a route parameter, which can be a part of the route url.

Tag Helpers for , <input asp-for="ModelProperty" />

will be converted as:

asp-for

Generates “type”, “name”, “id”, “data-validation” attributes for the ,

Tag Helpers for <label>

will be converted as:

asp-for

Generates “for” attribute for the

Client Side Validations

Data annotations on model properties

[Required]

publicDataTypePropertyName { get; set; }

“data-*” attributes in html tags [auto-generated with “asp-for” helper]

Import jQuery Validation Scripts

https://cdnjs.cloudflare.com/ajax/libs/ jquery/3.6.0/jquery.min.js

https://cdnjs.cloudflare.com/ajax/libs/ jquery-validate/1.19.3/jquery.validate.min.js

https://cdnjs.cloudflare.com/ajax/libs/ jquery-validation-unobtrusive/3.2.12/ jquery.validate.unobtrusive.min.js

Tag Helpers for

asp-append-version

  • Generates SHA512 hash of the image file as query string parameter appended to the file path.
  • It REGENERATES a new hash every time when the file is changed on the server. If the same file is requested multiple times, file hash will NOT be regenerated.

Tag Helpers for <script src="CDNUrl" asp-fallback-src="~/LocalUrl" asp-fallback-test="object"> 
<script> object || document.write("<script src='/LocalUrl'></script>"); </script>

asp-fallback-src

  • It makes a request to the specified CDNUrl at the “src” attribute.
  • It checks the value of the specified object at the “asp-fallback-test” tag helper.
• If its value is null or undefined (means, the script file at CDNUrl is not loaded), then it makes another request to the LocalUrl through another script tag.

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