Add a custom field for selecting a blog post

The following code creates a custom post selection field for the WP Form Master plugin, allowing users to select a post from a drop-down list in a form. This field also checks whether a valid selection has been made (if required), saves the ID or title of the selected post, and allows it to be added to forms using a shortcode.

Code

Explanations

Overall class structure

The WP_FormMaster_AddCustomField_PostSelect class defines and registers a new custom field that displays a drop-down list of posts. This field uses several WordPress filters and shortcuts to integrate with the form, control display, and manage validation.

Class variables

• $fieldname: Stores the field name, here “select-post”.
• $isRequired: Indicates whether the field is required, here set to true.

Class constructor

The class constructor adds several filters and a shortcode to integrate the custom field into the form:

1. allowed_block_types_all: Used to define which blocks are allowed in the WordPress form.
2. wpformmaster-form-post-select: Creates a shortcode to display the drop-down list of posts in the form.
3. wpfmaster_form_extractfields: Adds custom field attributes to the form.
4. wpformmaster_field_value: Extracts and interprets the value selected in the field for data recording.
5. wpfmaster_form_validate_field: Manages field validation to ensure that a post has been selected if the field is required.

Class methods

1. addRequiredError

This method is used to add an error message if the user does not select a post in the required field:

• Parameters: It receives several parameters such as $formID, $key (field name), $type, $field, $errors, $posts, and $files.
• How it works:
  • First, it checks whether the field is mandatory.
  • Then it checks whether a valid post is selected (existing and of type post).
  • If the field is empty or contains an invalid selection, it returns an error message: “Please select an item”.

2. getFieldValue

This method determines the value of the field to be saved in the form:

• Parameters: In addition to $value, $key, $type, $attrs, $posts, $files, it also takes $getInterpretValue to indicate whether the value should be interpreted.
• How it works:
  • If $getInterpretValue is true, it returns the title of the selected post.
  • Otherwise, it simply returns the post ID (as an integer).
  • If the field is empty, it returns the default value of $value.

3. extractFields

This method adds this field to the table of fields extracted by WP Form Master :

• How it works:
  • It adds a new field with a custom-select attribute and the name defined in $fieldname.
  • This field will then be available for the form, with the appropriate name to be identified when sending.

4. postSelectCallback

This method defines the HTML display of the selection field in the form:

• Parameters: It takes $atts to accept custom attributes passed to the shortcode.
• How it works:
  • Uses get_posts to retrieve all published posts.
  • Creates an HTML drop-down list where each option represents a post, displaying its title and storing its ID as a value.
  • If $isRequired is true, the field title will be marked with an asterisk to indicate that it is mandatory.

5. setBlocks

This method authorizes certain blocks for the WordPress block editor (Gutenberg) when the form is modified:

• How it works:
  • If the editor is in the context of a WP Form Master form (here identified by the post type fmaster_form), it authorizes the core/shortcode block.
  • This allows you to use the shortcode to add this specific field in the block editor.

Class instantiation

The line new WP_FormMaster_AddCustomField_PostSelect(); creates a new instance of the class and activates the custom field when the code is executed.

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