Magento : Get Category name,Product ID and SKU in Multi-selection field in admin for custom module which created using module creator

For this you can change on this file path

local/yourmodule/block/adminhtml/yourmodulename/edit/tab/form.phtml

you use below functions,

<?php

class Addon_Testing_Block_Adminhtml_Testing_Edit_Tab_Form extends Mage_Adminhtml_Block_Widget_Form
{
    // This for get category detail

    public function buildCategoriesMultiselectValues(Varien_Data_Tree_Node $node, $values, $level = 0)
    {
        $level++;
        //-----new start for only 3 level category
        if($level>3)
        {
        return $values;    
        }
        //-----new close
        $values[$node->getId()]['value'] =  $node->getId();
        $values[$node->getId()]['label'] = str_repeat("---", $level) . $node->getName();
       
        foreach ($node->getChildren() as $child)
        {
            $values = $this->buildCategoriesMultiselectValues($child, $values, $level);
           print_r($values); 
        }
       
        return $values;
    }
   
    public function load_tree()
    {
        $tree = Mage::getResourceSingleton('catalog/category_tree')->load();
   
        $store = 1;
        $parentId = 1;
   
        $tree = Mage::getResourceSingleton('catalog/category_tree')->load();
   
        $root = $tree->getNodeById($parentId);
       
        if($root && $root->getId() == 1)
        {
            $root->setName(Mage::helper('catalog')->__('Root'));
        }
       
        $collection = Mage::getModel('catalog/category')->getCollection()
            ->setStoreId($store)
            ->addAttributeToSelect('name')
            ->addAttributeToSelect('is_active');
       
        $tree->addCollectionData($collection, true);

        return $this->buildCategoriesMultiselectValues($root, array());   
    }
   
  //This is for product id
    function getProductCollection()
    {
       $model = Mage::getModel('catalog/product'); //getting product model
        $collection = $model->getCollection(); //products collection
       
       
                 $count = 0;
       
                foreach ($collection as $product) //loop for getting products
                {
                    $a = $count++;
                    $values[$a]['value'] = $a;
                    $values[$a]['label'] = $product->getId();
                 }                                          
                return $values;               
    }
   
     // This is for Product Sku
    function getProductCollectionskus()
    {
       $model = Mage::getModel('catalog/product'); //getting product model
        $collection = $model->getCollection(); //products collection
           
                $count = 0;
       
                foreach ($collection as $product) //loop for getting products
                {
                    $a = $count++;
                    $values[$a]['value'] = $a;
                    $values[$a]['label'] = $product->getSku();
                }                                             
                return $values;               
    }
  protected function _prepareForm()
  {
      $form = new Varien_Data_Form();
      $this->setForm($form);
      $fieldset = $form->addFieldset('testing_form', array('legend'=>Mage::helper('testing')->__('Item information')));
    
      $fieldset->addField('title', 'text', array(
          'label'     => Mage::helper('testing')->__('Title'),
          'class'     => 'required-entry',
          'required'  => true,
          'name'      => 'title',
      ));
     
       $fieldset->addField('girl', 'text', array(
          'label'     => Mage::helper('testing')->__('Girl'),
          'class'     => 'required-entry',
          'required'  => true,
          'name'      => 'girl',
      ));


      $fieldset->addField('filename', 'file', array(
          'label'     => Mage::helper('testing')->__('File'),
          'required'  => false,
          'name'      => 'filename',
      ));
   
     // Here, call above Functions
      $pids = $this->getProductCollection();
      $skus = $this->getProductCollectionskus();
      $categories_values = $this->load_tree();
      //echo "<pre>";
      //print_r($pids);
      //echo "</pre>";     
      //$categories_values = $this->load_tree();
        //echo '<pre>';            
        //print_r($skus);
        //echo "</pre>";
     
    $fieldset->addField('productid', 'multiselect', array(
                'name' => 'productid',
                'label' => Mage::helper('testing')->__('Select Product ID'),                  
                'required' => true ,               
                'values' => $pids,
               
                ));       
               
    $fieldset->addField('productsku', 'multiselect', array(
                'name' => 'productsku',
                'label' => Mage::helper('testing')->__('Select Product Sku'),                  
                'required' => true ,               
                'values' => $skus,               
                ));   
               
    $fieldset->addField('productsku', 'multiselect', array(
                'name' => 'productsku',
                'label' => Mage::helper('testing')->__('Select Category'),                  
                'required' => true ,               
                'values' => $categories_values,               
                ));              
               
     
     
       $fieldset->addField('content', 'editor', array(
          'name'      => 'content',
          'label'     => Mage::helper('testing')->__('Content'),
          'title'     => Mage::helper('testing')->__('Content'),
          'style'     => 'width:700px; height:500px;',
          'wysiwyg'   => false,
          'required'  => true,       
      ));
       
      $fieldset->addField('status', 'select', array(
          'label'     => Mage::helper('testing')->__('Status'),
          'name'      => 'status',
          'values'    => array(
              array(
                  'value'     => 1,
                  'label'     => Mage::helper('testing')->__('Enabled'),
              ),

              array(
                  'value'     => 2,
                  'label'     => Mage::helper('testing')->__('Disabled'),
              ),
          ),
      ));         
    
      if ( Mage::getSingleton('adminhtml/session')->getTestingData() )
      {
          $form->setValues(Mage::getSingleton('adminhtml/session')->getTestingData());
          Mage::getSingleton('adminhtml/session')->setTestingData(null);
      } elseif ( Mage::registry('testing_data') ) {
          $form->setValues(Mage::registry('testing_data')->getData());
      }
      return parent::_prepareForm();
  }
}