Magento custom module - cannot load layout file via XML

Question

A very common issue, but can't get my head around this one. Just not able to load the custom layout I want to display under the Admin tab content of my custom module via XML layout file (something like the attached image). This works while I add the same from controller's action.

I am currently doing the same under the controller action like this (working) -

public function indexAction() {
    $this->loadLayout()
         ->_setActiveMenu('module')
         ->_title($this->__('Module'));
    $this->_addContent($this->getLayout()->createBlock('adminhtml/template')->setTemplate('sync/index.phtml'));
    $this->renderLayout();
    //$this->getLayout()->setBlock('module_sync/');
}

Configured config.xml, app/design/adminhtml/default/default/layout/sync.xml (as mentioned in config.xml), and template file (as mentioned in layout file) - app/design/adminhtml/default/default/template/sync/index.phtml

The handlers seems to be fine, as checked by the code below, under the action:

$this->getLayout()->getUpdate()->getHandles()

As per the log of loaded files the mgt-commerce debugging module, the layout xml (module_sync.xml) is being parsed. Therefore, I am assuming things go haywire after that.

The configuration files:

<?xml version="1.0"?>
<config>
    <modules>
        <Module_Sync>
            <version>1.0.0</version>
        </Module_Sync>
    </modules>
    <global>
        <models>
            <!--
            Model alias referred to in install-1.0.0.php.
            -->
            <module_sync>
                <class>Module_Sync_Model</class>
                <resourceModel>module_sync_resource</resourceModel>
            </module_sync>
            <!--
            This alias must match the above <resourceModel/> value.
            -->
            <module_sync_resource>
                <class>Module_Sync_Model_Resource</class>
                <entities>
                    <!--
                    Table alias referred to in install-0.0.1.php.
                    -->
                    <config>
                         <!--
                        Actual name of the database table.
                        -->
                        <table>module_config</table>
                    </config>
                    <queue>
                         <!--
                        Actual name of the database table.
                        -->
                        <table>module_queue</table>
                    </queue>
                </entities>
            </module_sync_resource>
        </models>
        <resources>
            <!--
            This must match our folder name in the module sql folder.
            -->
            <module_sync_setup>
                <setup>
                    <!--
                    This defines which module the setup
                    scripts in this location belong to.
                    -->
                    <module>Module_Sync</module>
                    <!--
                    In each setup script, this
                    value determines the class of $this.
                    -->
                    <class>Mage_Core_Model_Resource_Setup</class>
                </setup>
            </module_sync_setup>
            <module_sync_read>
                <connection>
                    <use>core_read</use>
                </connection>
            </module_sync_read>
            <module_sync_write>
                <connection>
                    <use>core_write</use>
                </connection>
            </module_sync_write>
        </resources>
        <helpers>
            <module_sync>
                <class>Module_Sync_Helper</class>
            </module_sync>
        </helpers>
        <blocks>
            <sync>
                <class>Module_Sync_Block_Index</class>
            </sync>
        </blocks>
    </global>
    <admin>
        <routers>
            <adminhtml>
                <use>admin</use>
                <args>
                    <modules>
                        <module_sync before="Mage_Adminhtml">Module_Sync_Adminhtml</module_sync>
                    </modules>
                </args>
            </adminhtml>
        </routers>
    </admin>
    <adminhtml>
        <layout>
            <updates>
                <module_sync>
                    <file>module_sync.xml</file>
                </module_sync>
            </updates>
        </layout>
    </adminhtml>
    <default>
        <api>
            <cp>
                <url>dev.module.com/api</url>
                <routes>
                    <user>users</user>
                </routes>
            </cp>
            <ms>
                <url>162.13.184.69/api/v2</url>
                <routes>
                    <category>categories</category>
                </routes>
            </ms>
        </api>
    </default>
</config>

2. Layout file - app/design/adminhtml/default/default/module_sync.xml

<?xml version="1.0"?>
    <layout>
        <module_sync_index>
            <reference name="head">
                <action method="setTitle" translate="title">
                    <title>Module</title>
                </action>
            </reference>
            <reference name="content">
                <block type="module_sync/adminhtml_index"     template="sync/index.phtml"/>
            </reference>
        </module_sync_index>
    </layout>

3. Template file (app/design/adminhtml/default/default/template/sync/index.phtml)

   <div class="content">
       <h3 class="mobi-text">Module Signup</h3>
       <form>
           <div>
               <input type="text" name="name" placeholder="Enter your Name">
           </div>
           <div>
               <input type="text" name="email" placeholder="Enter your Email">
           </div>
           <div>
               <input type="text" name="url" placeholder="Enter Store URL">
           </div>
           <div>
               <input type="text" name="no" placeholder="Enter your phone number">
           </div>
           <div>
               <input type="submit" class="btn btn-red btn-lg" value="Sign Up">
           </div>
           <div>
               <p>Already have an account? <a href="">Sign In</a></p>
           </div>
       </form>
   </div>
   

Already read and tried these

Admin layout file not loading in custom module

Load Custom Admin Template

custom module layout not working

and some more.

Answer 1

First check if the layout handle is correct.
Add this line in the controller to see the layout handle

echo $this->getFullActionName();

I have a feeling it will print something like this adminhtml_module_sync_index. This is the layout handle you have to use in the layout file.
Also, just to be save, add a name and alias to the block from the content section.
Something like this:

    <adminhtml_module_sync_index><!--put here what you get from the echo in the controller -->
        <reference name="head">
            <action method="setTitle" translate="title">
                <title>Module</title>
            </action>
        </reference>
        <reference name="content">
            <block type="module_sync/adminhtml_index" template="sync/index.phtml" as="index" name="index" />
        </reference>
    </adminhtml_module_sync_index>

Answer 2

I was facing the same issue and I see this thread very old. But, I think, this might help someone who looks at this thread in future:

I had the layout handles correct, my block class was getting executed. But whatever was there in the template file was not coming through!

So, I figured out that the method protected function _toHtml() in block class was the culprit.

If I wrote something in this method, it was getting displayed. However, if I leave this method blank and write html code in my template file, it was not getting displayed.

I figured out that when we need the html content from template files, the block class must not have this method protected function _toHtml(). I think it overwrites whatever coming from the template file.