The Form Tag Helper

The form tag helper renders an action attribute within a form element. It also includes an anti-forgery token for request verification. If a method attribute is not specified in the form element, the form tag helper will render one with a value of post.

The form tag helper's primary role is to generate an action attribute from the parameters passed to its custom attributes. Therefore, if you try to provide an action attribute to the form tag helper in addition to the custom attributes, an exception will be raised.

Attribute Description
action The name of the action method on an MVC controller
all-route-data1 Multiple route parameter values
antiforgery7 Specifies whether an anti-forgery token is rendered.
area The name of the MVC area
controller The name of the MVC controller
fragment2 The fragment in the URL
host The domain
page3 The Razor page to link to
page-handler4 The Razor page handler method to invoke
protocol The protocol (http, https, ftp etc)
route5 The name of the route
route-6 A single route parameter value

Notes

  1. If the target URL for the action includes multiple route parameters, their values can be packaged as a Dictionary<string, string> and passed to the all-route-data parameter:

    @{   
        var d = new Dictionary<string, string>
            {
               { "key1", "value1" },
               { "key2", "value2" }
            };
    }
    
    <form asp-all-route-data="d">...</form>
    

    If the route has parameters defined, the form tag helper will output the values as URL segments: <form action="/Page/value1/value2">...</form>. If it doesn't, the route parameters will be appended to the URL as query string values: <form action="/Page?key1=value1&amp;key2=value2" method="post">...</form>.

  2. The fragment is the value after a hash or pound sign (#) in a URL used to identify a named portion of a document. The "Notes" heading above has an identity value of "notes" and can be referenced in a URL using the anchor tag helper like this:

    <form asp-fragment="notes">...</form>
    

    producing this HTML: <form action="/Page#notes" method="post">...</form>. It should be noted that fragments have no influence on the submission of a form.

  3. The name of the Razor page to link to must be provided without the file extension:

    <form asp-page="page">...</form>
    

    If no page name is specified, the tag helper will generate a link to the current page.

  4. The page handler method name will appear as a query string value unless it has been included as a route parameter for the target page.

  5. Razor pages doesn't support named routes. This parameter will only be used for MVC routes.

  6. The route- parameter enables you to specify the value for a single route value. The route parameter name is added after the hyphen. Here, the route parameter name is "key1":
    <form asp-route-key1="value1">...</form>
    This renders as
    <form action=/Page/value1" method="post">...</form>
    if the key1 parameter is defined as part of the page's route template, or
    <form action="/Page?key1=value1" method="post">...</form>
    if not.

  7. The anti-forgery token is rendered as a hidden input named __RequestVerificationToken. It will be rendered by default, unless the form has an action attribute specified, the form's method is set to GET or the antiforgerytoken value is set to false.

Last updated: 27/02/2018 08:22:05

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