how do i extend a magento class from core?

Question

I know that it is not safe to modify the core, so i want to extend a class. My need is to add a new button. In the image below you can see where:

So, I created a module for that. I think the idea is that my module is triggered when I clicked on a attribute set. I have absoluty no idea how to do that. I tried smth like this: config.xml content:

   <?xml version="1.0"?>
<config>
    <modules>
        <Netgr_Gradd>
            <version>1.0.0</version>
        </Netgr_Gradd>
    </modules>
    <global>
        <blocks>
            <netgr_gradd>
                <class>Netgr_Gradd_Block</class>
            </netgr_gradd>
            <adminhtml>
                <rewrite>
                    <catalog_product_attribute_set_main>Netgr_Gradd_Block_Adminhtml_Addgroup</catalog_product_attribute_set_main>
                </rewrite>
            </adminhtml>
        </blocks>
    </global>

</config>

After in controllers/AddgroupController.php content is :

<?php

class Netgr_Gradd_Adminhtml_AddgroupController extends Mage_Adminhtml_Controller_Action
{

    public function indexAction(){
        echo   11111;
    }
}

Here I tried to extend from the core class, the function that adds a new button, but with no result. Can anyone help me with this ?

The content of adminthml.xml is:

  <?xml version="1.0"?>
<config>
    <admin>
        <routers>
            <adminhtml>
                <args>
                    <modules>
                        <netgr_gradd before ="Mage_Adminhtml">Netgr_Gradd_Adminhtml</netgr_gradd>
                    </modules>
                </args>
            </adminhtml>
        </routers>

    </admin>

</config>

and this is the content from Block/Adminhtml/Addgroup.php:

class Netgr_Gradd_Block_Adminhtml_Addgroup extends Mage_Adminhtml_Block_Catalog_Product_Attribute_Set_Main
{

     public function  __construct() {

        parent::_prepareLayout();

        $this->_addButton('button_id', array(
            'label'     => Mage::helper('xxx')->__('Some action'),
            'onclick'   => 'jsfunction(this.id)',
            'class'     => 'go'
        ), 0, 100, 'header', 'header');
    }
}

Answer 1

So it appears you are trying to rewrite a controller when you could simply rewrite the block Mage_Adminhtml_Block_Catalog_Product_Attribute_Set_Main.

<config>
    <global>
        <blocks>
            <netgroup_attributegrouping>
                <class>Netgroup_Attributegrouping_Block</class>
            </netgroup_attributegrouping>
            <adminhtml>
                <rewrite>
                    <catalog_product_attribute_set_main>Netgroup_Attributegrouping_Block_Adminhtml_Addgroup</catalog_product_attribute_set_main>
                </rewrite>
            </adminhtml>
        </blocks>
    <global>
</config>

Then change your class to be class Netgroup_Attributegrouping_Block_Adminhtml_Addgroup and put it under the Block/Adminhtml folder of your extension with the filename Addgroup.php

Then add your _prepareLayout function changes and call parent::_prepareLayout()

Update for button

Now that I see you are wanting to add a button you can see in the template app/design/adminhtml/default/default/template/catalog/product/attribute/set/main.phtml all the calls to the blocks add button functions like getResetButtonHtml. So the steps to add a new button would be as follows:

1. Rewrite this block to use your own template. Your template can simply be a copy of the default one,
2. Add a new button call <?php echo $this->getYourButtonHtml() ?> into your template with the others,
3. In your new block add the function getYourButtonHtml which will simply contain return $this->getChildHtml('your_button');
4. Update your block's prepareLayout function to add the button,

So in the end your class should look as follows:

class Netgr_Gradd_Block_Adminhtml_Addgroup extends Mage_Adminhtml_Block_Catalog_Product_Attribute_Set_Main
{

protected function _construct() {
    //This should just be a copy of catalog/product/attribute/set/main.phtml so you can edit it
    $this->setTemplate('netgroup/catalog/product/attribute/set/main.phtml');
}

public function _prepareLayout() {
    $this->setChild('your_button',
        $this->getLayout()->createBlock('adminhtml/widget_button')->setData(array(
            'label'     => Mage::helper('catalog')->__('Your Button Label'),
            'onclick'   => 'your button on click',
            'class'     => 'your-button-class'
    )));
    return parent::_prepareLayout();
}

public function getYourButtonHtml() {
    return $this->getChildHtml('your_button');
}
}

Then for the template simple make a copy of app/design/adminhtml/default/default/template/catalog/product/attribute/set/main.phtml to for example app/design/adminhtml/default/default/template/netgroup/catalog/product/attribute/set/main.phtml then make a small change and add a new button html section:

<td class="form-buttons">
    <?php echo $this->getBackButtonHtml() ?>
    <?php echo $this->getResetButtonHtml() ?>
    <?php echo $this->getDeleteButtonHtml() ?>
    <?php echo $this->getSaveButtonHtml() ?>
    <?php echo $this->getYourButtonHtml() ?>
</td>