Adding a custom file field to the campaign form

functions.php

<?php  
/**
 * This function adds a custom text field to the campaign submission
 * form, as well as the admin campaign editor, campaign emails, and
 * campaign export.
 *
 * Note: This example requires Ambassadors 2+. For an example that worked
 * on previous version, see the link below.
 *
 * @see https://github.com/Charitable/library/blob/master/extensions/ambassadors/legacy/add-text-field.php
 *
 * @return void
 */
add_action( 'init', function( $fields ) {
	$fields = charitable()->campaign_fields();

	// Create the field.
	$field = new Charitable_Campaign_Field(
		'custom_file_field',
		[
			'label'          => 'Custom File Field',
			'data_type'      => 'meta',
			'campaign_form'  => [
				'required' => false,
				'type'     => 'file',
				'section'  => 'campaign-details',
				'priority' => 30,
			],
			'admin_form'     => [
			    'type'      => 'content',
				'content'   => '',
				'base_path' => trailingslashit( __DIR__ ),
				'view'      => 'my-custom-file-field-view',
				'priority'  => 1,
			],
			'show_in_export' => true,
			'email_tag'      => true,
		]
	);

	// Register the field.
	$fields->register_field( $field );
} );


/**
 * Get the uploaded file from the $_FILES array and add it to the 
 * meta data to be saved for the campaign.
 *
 * @param  array $values The meta values.
 * @param  Charitable_Data_Processor $data_processor The data processor. 
 * @return array
 */
add_filter( 'charitable_campaign_submission_meta_data', function( $values, $data_processor ) {
	if ( isset( $_FILES ) && isset( $_FILES['custom_file_field'] ) ) {
		$attachment_id = $data_processor->upload_attachment( 'custom_file_field', $values['ID'] );

		if ( ! is_wp_error( $attachment_id ) ) {
			$submitted[ 'custom_file_field' ] = $attachment_id;

			/* Delete the previously upload file. */
			if ( ! empty( $value['ID'] ) ) {
				$old_file = get_user_meta( $values['ID'], 'custom_file_field', true );

				if ( ! empty( $old_file ) ) {
					wp_delete_attachment( $old_file );
				}
			}
			
			$values['custom_file_field'] = $attachment_id;
		}
	}

	return $values;
}, 10, 2 );

/**
 * Make the PDF field a permitted field. 
 *
 * Note that the name of the filter includes 'custom_file_field', which should be
 * replaced with the field id. If you are defining multiple file fields which should
 * accept non-image fields, you will need to provide multiple filter functions like 
 * below, with the corresponding field key.
 *
 * @param  array $mime_types The list of permitted mime types for this field.
 * @return array
 */
add_filter( 'charitable_file_custom_file_field_allowed_mimes', function( $mime_types ) {
	$mime_types['pdf'] = 'application/pdf';
	return $mime_types;
} );

In order to display the file as a link in the admin, you need to configure the base_path and view arguments in the admin_form setting to correspond to a PHP file

For example, in the example above, the view file would be expected in the same directory where this function is defined, and would be called my-custom-file-field-view.php.

In the view file, there is a $view_args variable available which is an array. It includes the ID of the uploaded file with $view_args['value']. You can then display the file path using get_attached_file():

$file_id = $view_args['value'];

echo get_attached_file( $file_id );

This is the default set of supported mime types:

$allowed_mimes = array(
	'jpg|jpeg|jpe' => 'image/jpeg',
	'gif'          => 'image/gif',
	'png'          => 'image/png',
	'bmp'          => 'image/bmp',
	'tif|tiff'     => 'image/tiff',
	'ico'          => 'image/x-icon',
);