php - Get custom phtml content using observer on core_block_abstract_to_html_after event -

i have custom block append under existing core block in order view page in admin panel of magento.

i developed custom module.

in order avoid modification of core template phtml file load custom block, try follow best practices , built observer on core_block_abstract_to_html_after

if want know why read more 2 excellent articles above

http://www.atwix.com/magento/best-practices/

http://inchoo.net/magento/how-you-could-build-your-magento-extensions-without-view-files/

however while block, want append, contain lots of html want put html in custom phtml file , not directly in php, make more customizable designers.

i created phtm file in following folder

app\design\adminhtml\default\default\template\custommodulefolder\customhtmlfileforadminorderview.phtml 

but how load phtml content observer ?

<adminhtml>         <events>             <core_block_abstract_to_html_after>                 <observers>                     <custommodule>                         <class>namespace_custommodule_model_observer</class>                         <method>renderblockcustomdadmin</method>                     </referencefield>                 </custommodule>             </core_block_abstract_to_html_after>         </events>     </adminhtml> 

and method in observer.php

    public function renderblockcustomdadmin($observer = null)         {             if (!$observer) {                 return;             }              if ('order_info' == $observer->getevent()->getblock()->getnameinlayout()) {                  if (!mage::getstoreconfig('advanced/modules_disable_output/'.self::module_name)) {                      $transport = $observer->getevent()->gettransport();  // here find way load content of custom of phtml                     $htmfromablock= function_which_will_allow-me_to_get_content_phtmlfile()                      $transportoldhtml =$transport->gethtml();                     $transport->sethtml($transportoldhtml.'<br />'.$htmfromablock);                 }             }              return $this;         } 

creating block easy when layout (it matter of calling createblock() block type want , settemplate() template want use).
, can layout block.

so in case :

$observer->getevent()          ->getblock()          ->getlayout()          ->createblock('adminhtml/template')          ->settemplate('custommodulefolder/customhtmlfileforadminorderview.phtml')          ->tohtml();