volution's API Crash Course

if ($modx->event->name == 'OnWebPageInit') {
  
  $modx->setDebug(E_ALL & ~E_NOTICE); // sets error_reporting to everything except NOTICE remarks
  $modx->setLogLevel(modX::LOG_LEVEL_DEBUG);
  
  
  $resourceId1 = $modx->resourceIdentifier; // WORKS
  $resourceId2 = $modx->resource->get('id'); //FAILS - not sure why
  
  $modx->log(modX::LOG_LEVEL_INFO, 'ID 1: ' . $resourceId1 );
  $modx->log(modX::LOG_LEVEL_INFO, 'ID 2: ' . $resourceId2 );
}

class myOwnClass {
     function __construct(modX &$modx) {
         $this->modx =& $modx;
     }
     public function myFunction() {
         return $this->modx->resource->get('id');
     }
}

$classObj = new myOwnClass($modx);
$resourceId = $classObj->myFunction();

<?php
include_once $modx->getOption('core_path').'components/myProject/snippet.php';

<?php
include_once MODX_BASE_PATH . 'myProject' . DIRECTORY_SEPARATOR . 'classes' . DIRECTORY_SEPARATOR . 'parent.class.php';
include_once MODX_BASE_PATH . 'myProject' . DIRECTORY_SEPARATOR . 'classes' . DIRECTORY_SEPARATOR . 'child.class.php';

$myObject = new myChildClass();
$output = $myObject->childFunction($configArray);
echo $output;

<?php
class myParentClass {

    public $configArray;

    // as your suggestion
    public function __construct(modX &$modx) {
        $this->modx =& $modx;
    }

    public function parentFunction($buffer, $configArray) {
      // don't mind about the $configArray, it's used elsewhere
      
      $buffer = str_replace(SOME_PATH . 'index.php', MODX_SITE_URL . '/index.php?id=' . $modx->resource->get('id') , $buffer);
      
      return $buffer;
    }
}

<?php
class myChildClass extends myParentClass {

    public $configArray;

    public function childFunction($configArray) {

        ob_start();
        require(SOME_PATH . 'index.php');
        $buffer = ob_get_contents();
        ob_end_clean();

        // buffering the output
        $output = parent::parentFunction($buffer, $configArray);
        return $output;
    }
}

 $modx->setPlaceholder ($name, $value);