Adding a button to Sales Order View using observer not working

Question

I am trying to add a simple generic button to the Sales Order View page using the adminhtml_widget_container_html_before event but no matter what I try the button will not appear.

Here is my code:

/app/etc/modules/ZeroBars_Approvebutton.xml

<?xml version="1.0"?>
<config>
    <modules>
        <ZeroBars_Approvebutton>
            <active>true</active>
            <codePool>local</codePool>
        </ZeroBars_Approvebutton>
    </modules>
</config> 

/app/code/local/ZeroBars/Approvebutton/etc/config.xml

<config>
    <modules>
        <ZeroBars_Approvebutton>
            <version>0.0.1</version>
        </ZeroBars_Approvebutton>
    </modules>
    <global>
    <models>
        <zerobars_approvebutton>
            <class>ZeroBars_Approvebutton_Model</class>
        </zerobars_approvebutton>
    </models>
    <helpers>
        <zerobars_approvebutton>
            <class>ZeroBars_Approvebutton_Helper</class>
        </zerobars_approvebutton>
    </helpers>
    <adminhtml>
    <events>
        <adminhtml_widget_container_html_before>
            <observers>
                <zerobars_approvebutton>
                    <class>zerobars_approvebutton/observer</class>
                    <method>adminhtmlWidgetContainerHtmlBefore</method>
                </zeroBars_approvebutton>
            </observers>
        </adminhtml_widget_container_html_before>
    </events>
</adminhtml>
</config>

/app/code/local/ZeroBars/Approvebutton/Model/Observer.php

<?php

Class ZeroBars_Approvebutton_Model_Observer
{
    public function adminhtmlWidgetContainerHtmlBefore($event) {

        $block = $event->getBlock();
        if ($block instanceof Mage_Adminhtml_Block_Sales_Order_View) {
            $block->addButton('do_something_crazy', array(
                'label'     => Mage::helper('module')->__('Button'),
                'onclick'   => "setLocation('{some location}')",
                'class'     => 'go'
            ));           
        }
    }
}

The method for adding a button on the page seems pretty straightforward so I am not sure why it is not working. Is there a possibility that another extension is overriding it?

Answer 1

In your config.xml you have a <global> node however that is never closed out add </global> before <adminhtml> and it should work everything else looks OK to me.