Call to a member function insert() on a non-object Magento - magento

Question

I am Using Observer Event in my custom module's Config.xml
<controller_action_layout_render_before>
<observers>
<Test_Check_Model_Observer>
<class>Test_Check_Helper_Data</class>
<method>checkValidi</method>
</Test_Check_Model_Observer>
</observers> </controller_action_layout_render_before>
Now in Test/Check/Helper/Data checkValidi Method I am inserting a block in Content.
>
class Test_Check_Helper_Data extends Mage_Core_Helper_Abstract {
> public function checkValidi($observer) {
> $layout = Mage::app()->getLayout();
> $content = $layout->getBlock('content');
> $block = 'hello! I am Working';
> $content->insert($block);
> }
But In Frontend When I am Filling Checkout billing and other information it gives me an Error Call to a member function insert() on a non-object in right side bar of Your Checkout Progress ,Please Give me any Solution for that Thanks

Answer 1

If you look at layout of checkout module checkout.xml you can see that some handles do not have content block. Eg, checkout_onepage_progress_billing or checkout_onepage_progress_shipping
So, you will get non-object error with your code. I think you should check $block variable before calling method.
$layout = Mage::app()->getLayout();
$content = $layout->getBlock('content');
if ($content) {
$block = 'hello! I am Working';
$content->insert($block);
}

Answer 2

It is not good idea to call helper from observer.
Observer always call a model file ,it did not class
i have modify and code config.xml code is
<global>
<models>
<testcheck>
<class>Test_Check_Model</class>
</testcheck>
</models>
</global>
<events>
<controller_action_layout_render_before>
<observers>
<test_check_codel_observer>
<type>singleton</type>
<class>testcheck/observer</class>
<method>your_function_name</method>
</test_check_codel_observer>
</observers>
</controller_action_layout_render_before>
</events>
And then Create Observer Observer.php file Under app/code/YourcodePoll/Test/Check/Model/
and below
code in Observer.php
is
<?php class Test_Check_Model_Observer
{
public function your_function_name($observer){
$block = $this->getLayout()
->createBlock('core/text', 'example-block')
->setText('<h1>This is a text block</h1>');
$observer->getEvent()->getLayout()->getBlock('content')->append($block);
//$observer->getEvent()->getLayout()->getUpdate();
}
}