Magento 1.9: I want rewrite form.phtml

Question

I want to add some custom tab in Sales order shipping page so i try to rewrite below way

config.xml

     <?xml version="1.0"?>
<config>
  <modules>
    <MPS_Delivery>
      <version>0.1.0</version>
    </MPS_Delivery>
  </modules>
  <frontend>
    <routers>
      <delivery>
        <use>standard</use>
          <args>
            <module>MPS_Delivery</module>
            <frontName>delivery</frontName>
          </args>
      </delivery>
    </routers>
        <layout>
          <updates>
            <delivery>
              <file>delivery.xml</file>
            </delivery>
          </updates>
        </layout>
  </frontend>
  <global>
    <helpers>
      <delivery>
        <class>MPS_Delivery_Helper</class>
      </delivery>
    </helpers>
    <blocks>
      <delivery>
        <class>MPS_Delivery_Block</class>
      </delivery>
    <adminhtml>
       <!--  <rewrite>
            <sales_order_view_info>MPS_Delivery_Block_Sales_Order_View_Info</sales_order_view_info>
        </rewrite>  -->
         <!-- <rewrite>
            <sales_order_shipment_create_form>MPS_Delivery_Block_Sales_Order_Shipment_Create_Form</sales_order_shipment_create_form>
        </rewrite> --> 
        <rewrite>
    <sales_order_shipment_create_form>MPS_Delivery_Block_Sales_Order_Shipment_Create_Form</sales_order_shipment_create_form>
</rewrite>

    </adminhtml>
    </blocks>
    <models>
      <delivery>
        <class>MPS_Delivery_Model</class>
        <resourceModel>delivery_mysql4</resourceModel>
      </delivery>
      <delivery_mysql4>
        <class>MPS_Delivery_Model_Mysql4</class>
        <entities>        
              <delivery>
                <table>delivery</table>
              </delivery>
        </entities>
      </delivery_mysql4>
    </models>
    <resources>
      <delivery_setup>
        <setup>
          <module>MPS_Delivery</module>
        </setup>
        <connection>
          <use>core_setup</use>
        </connection>
      </delivery_setup>
      <delivery_write>
        <connection>
          <use>core_write</use>
        </connection>
      </delivery_write>
      <delivery_read>
        <connection>
          <use>core_read</use>
        </connection>
      </delivery_read>
    </resources>
  </global>
  <admin>
    <routers>
      <delivery>
        <use>admin</use>
        <args>
          <module>MPS_Delivery</module>
          <frontName>admin_delivery</frontName>
        </args>
      </delivery>
    </routers>
  </admin>
  <adminhtml>
    <menu>
      <delivery module="delivery">
        <title>Delivery</title>
        <sort_order>100</sort_order>
        <children>
          <deliverybackend module="delivery">
            <title>Backend Page Title</title>
            <sort_order>0</sort_order>
            <action>admin_delivery/adminhtml_deliverybackend</action>
          </deliverybackend>
          <delivery module="delivery">
            <title>Manage Delivery</title>
            <sort_order>0</sort_order>
            <action>admin_delivery/adminhtml_delivery</action>
          </delivery>
        </children>
      </delivery>
    </menu>
    <acl>
      <resources>
        <all>
          <title>Allow Everything</title>
        </all>
        <admin>
          <children>
            <delivery translate="title" module="delivery">
              <title>Delivery</title>
              <sort_order>1000</sort_order>
              <children>
          <deliverybackend translate="title">
            <title>Backend Page Title</title>
          </deliverybackend>
          <delivery translate="title">
            <title>Manage Delivery</title>
            <sort_order>0</sort_order>
          </delivery>
              </children>
            </delivery>
          </children>
        </admin>
      </resources>
    </acl>
    <layout>
      <updates>
        <delivery>
          <file>delivery.xml</file>
        </delivery>
      </updates>
    </layout>
  </adminhtml>
</config> 

delivery.xml

<adminhtml_sales_order_shipment_new>
      <reference name="content">
          <action method="setTemplate"><template>delivery/sales/order/shipment/create/form.phtml</template></action>
      </reference>
    </adminhtml_sales_order_shipment_new>

Form.php

<?php
class MPS_Delivery_Block_Adminhtml_Sales_Order_Shipment_Create_Form extends Mage_Adminhtml_Block_Sales_Order_Shipment_Create_Form
{
    public function myFunction() // Your function
    {
        echo "Hello";
    }

But it's not working i don't know what mistake i made here

Answer 1

If you want to override sales/order/shipment/create/form.phtml file with your own file then you need to use below code in your delivery.xml file.

<adminhtml_sales_order_shipment_new>
  <reference name="form">
      <action method="setTemplate"><template>delivery/sales/order/shipment/create/form.phtml</template></action>
  </reference>
</adminhtml_sales_order_shipment_new>

To use a function from your block, first you need to make changes to your config.xml add below lines.

<rewrite>
    <sales_order_shipment_create_form>MPS_Delivery_Block_Adminhtml_Sales_Order_Shipment_Create_Form</sales_order_shipment_create_form>
</rewrite>

Now create a new file in app\code\local\MPS\Delivery\Block\Adminhtml\Sales\Order\Shipment\Create\Form.php

<?php
class MPS_Delivery_Block_Adminhtml_Sales_Order_Shipment_Create_Form extends Mage_Adminhtml_Block_Sales_Order_Shipment_Create_Form
{
    public function myFunction() // Your function
    {
        echo "Hello";
    }
}

Now you can use this function in your form.phtml