How can I add block through XML layout file, and not programmatically, through controller?

Question

How can I add a block through XML layout file, and not programaticaly, through controller?

I have my block and I want to use it in a template that already exists (catalog/category/view.phtml).

How can I do this without going in and changing a controller, and without changing the catalog/category/view.phtml directly?

I want to add this block somewhere in an already existing template through XML, and not programatically.

This is part of my block:

class Mynamespace_Mymodule_Block_Myblock extends Mage_Core_Block_Template
{
    public function _construct()
    {
        $this -> setTemplate("mynamespace_mymodule/myblock.phtml");
        return parent::_construct();

    }

    public function getItemsByCategoryAndUseState($category, $use_state) {
        return "some used or new items";
    }
}

This is config.xml of my module:

<config>
<modules>
    <Mynamespace_Mymodule>
        <version>3.0.0.1</version>
    </Mynamespace_Mymodule>
</modules>
<global>
    <blocks>
        <mynamespace_mymodule>
            <class>Mynamespace_Mymodule_Block</class>
        </mynamespace_mymodule>
    </blocks>
</global>
<frontend>
    <layout>
        <updates>
            <mynamespace_mymodule>
                <file>mynamespace_mymodule.xml</file>
            </mynamespace_mymodule>
        </updates>
    </layout>

</frontend>

This is my package/theme/layout/mynamespace_mymodule.xml:

<layout version="0.1.0">
    <catalog_category_view> 
        <reference name="product_list"> 
            <block type="mynamespace_mymodule/myblock" name="myblock" after="-" /> 
        </reference> 
    </catalog_category_view>
</layout> 

Thanks.

Answer 1

you can add block with this xml code

<catalog_category_view>
    <reference name="content">
        <block type="mymodule/myblock"  after="-" />
     </reference>
</catalog_category_view>

add this is <frontend> tag not in <global>

     <frontend>
      <layout>
        <updates>
            <mynamespace_mymodule>
                <file>mynamespace_mymodule.xml</file>
            </mynamespace_mymodule>
        </updates>
      </layout>
    </frontend>

Answer 2

Solved it partially by using methods of the block in template. I just:

1. Created the block
2. Declared the block in module's config.xml
3. Using it in the template (a .phtml file) like so:

4. echo $this -> getLayout() 
       -> createBlock('mymodule/myblock') 
       -> toHtml();
   

I want to do it just with .XML layout updates though.