Demonstrates validating a single field of the form created by the framework. This is a sample plugin introduced in the tutorial, Validate Submitted Form Data of a Single Field (http://en.michaeluno.jp/admin-page-framework/tutorials-v3/07-validate-submitted-form-data-of-a-single-field/).

tutorials-07-validate-single-field.php

<?php
/*
 *  Plugin Name:    Admin Page Framework Tutorial 07 - Validate Single Field 
 *  Plugin URI:     http://en.michaeluno.jp/admin-page-framework
 *  Description:    Validates a single field of the form created by the framework.
 *  Author:         Michael Uno
 *  Author URI:     http://michaeluno.jp
 *  Version:        1.0.0
 *  Requirements:   PHP 5.2.4 or above, WordPress 3.4 or above. Admin Page Framework 3.0.6 or above
 */

// Set your own path here
include( dirname( __FILE__ ) . '/library/apf/admin-page-framework.php' );
    
class APF_ValidateSingleField extends AdminPageFramework {

    public function setUp() {
        
        $this->setRootMenuPage( __( 'Validate Form Data', 'admin-page-framework-tutorials' ) );    // where to belong
        $this->addSubMenuItem(
            array(
                'title'           => __( '7. Validate Single Field', 'admin-page-framework-tutorials' ),    // page and menu title
                'page_slug'       => 'apf_tutorial_single_field_validation'    // page slug
            )
        );
                    
        $this->addSettingFields(
            array(    
                'field_id'        => 'url',
                'title'           => __( 'URL', 'admin-page-framework-tutorials' ),
                'type'            => 'text',
                'default'         => 'http://wordpress.org',
            ),        
            array(    
                'field_id'        => 'submit',
                'type'            => 'submit',
            )
        );
        
    }
        
    /**
     * The pre-defined validation callback method.
     * 
     * Notice that the method name is validation_{instantiated class name}_{field id}.
     * 
     * @param    string|array    $sInput        The submitted field value.    
     * @param    string|array    $sOldInput    The old input value of the field.
     */
    public function validation_APF_ValidateSingleField_url( $sInput, $sOldInput ) {
        
        // Set a flag
        $_bIsValid = true;
        
        // Prepare an field error array.
        $_aErrors  = array();
        
        // Use the debug method to see what are passed.
        // $this->oDebug->log( $sInput );
        
        // Check if a url is passed
        if ( ! filter_var( $sInput, FILTER_VALIDATE_URL ) ) {
            
            $_bIsValid = false;

            // $variable[ 'field_id' ]
            $_aErrors['url'] = __( 'The value must be a url:', 'admin-page-framework-tutorials' ) . ' ' . $sInput;
            
        }
                 
        // An invalid value is found.
        if ( ! $_bIsValid ) {
        
            // Set the error array for the input fields.
            $this->setFieldErrors( $_aErrors );        
            $this->setSettingNotice( __( 'There was something wrong with your input.', 'admin-page-framework-tutorials' ) );
            return $sOldInput;
            
        }        
        
        return $sInput;
        
    }
    
}

new APF_ValidateSingleField;