how to call a phtml file in the success page in a proper way?

Question

I have a template in template/checkout/onepage/hello.phtml

I want to include this phtml file in the success page, i.e template/checkout/success.phtml

So I have created a block in the checkout.xml inside the "checkout_onepage_success" handle as:

<checkout_onepage_success translate="label">
    <label>One Page Checkout Success</label>
    <reference name="root">
        <action method="setTemplate"><template>page/2columns-right.phtml</template></action>
    </reference>
    <reference name="content">
         <block type="core/template" name="onepagehello" template="checkout/onepage/hello.phtml"/>
        <block type="checkout/onepage_success" name="checkout.success" template="checkout/success.phtml"/>
    </reference>
</checkout_onepage_success>  

And this phtml file gets rendered in the success page on the top of the page.

When I write getChildHtml(onepagehello); in success.phtml page, then nothing comes.

1. I want to know when getChildHtml() works and when the block gets rendered ?
2. I want to get "hello.phtml" from getChildHtml(), so that I can put this block wherever necessary throughout the page.

Answer 1

The layout is a hierarchy of blocks and getChildHtml() can only render the children of the current block.

Right now your hierarchy looks like this:

root
+-- content
    +-- onepagehello
    +-- checkout.success

but you need this:

root
+-- content
    +-- checkout.success
        +-- onepagehello

To add a new block to an existing parent block, use <reference>:

<checkout_onepage_success>
    <reference name="checkout.success">
         <block type="core/template" name="onepagehello" template="checkout/onepage/hello.phtml"/>
    </reference>
</checkout_onepage_success>  

Answer 2

Just add element as="NAME" on your block like this

<block type="core/template" name="onepagehello" template="checkout/onepage/hello.phtml" as="hello"/>

you can call like this

getChildHtml('hello');