Joomla 3 helloworld component category

Question

After i follow the Joomla "Developing an MVC Component" document until step 15- "Adding ACL" everything works. Then I tried add a new view "category", but it did not work.

Here is my code:

In admin fields folder I created a hellocategory.php most code same with helloword,just change

protected $type = 'HelloCategory';

/**
 * Method to get a list of options for a list input.
 *
 * @return  array  An array of JHtml options.
 */
protected function getOptions()
{
    $db    = JFactory::getDBO();
    $query = $db->getQuery(true);
    // custom
    $query->select('#__categories.id as id,#__categories.title as category,#__categories.extension as exten');
    $query->from('#__categories');  
    $query->where($db->quoteName('extension') . ' LIKE '. $db->quote('com_helloworld'));
    // end custom
    $db->setQuery((string) $query);
    $messages = $db->loadObjectList();
    $options  = array();
    if ($messages)
    {
        foreach ($messages as $message)
        {
            $options[] = JHtml::_('select.option', $message->category);
        }
    }

    $options = array_merge(parent::getOptions(), $options);

    return $options;

view.html.php

class HelloWorldViewCategory extends JViewLegacy
{
    /**
     * Display the Hello World view
     *
     * @param   string  $tpl  The name of the template file to parse; automatically searches through the template paths.
     *
     * @return  void
     */
    function display($tpl = null)
    {
        // Assign data to the view
        $category = $this->get('Item');

        // Check for errors.
        if (count($errors = $this->get('Errors')))
        {
            JLog::add(implode('<br />', $errors), JLog::WARNING, 'jerror');

            return false;
        }

        // Display the view
        parent::display($tpl);
    }
}

default.xml

<layout title="Category">
        <message>category</message>
</layout>
<fields
        name="request"
        addfieldpath="/administrator/components/com_helloworld/models/fields"
        >
    <fieldset name="request">
        <field
                name="id"
                type="hellocategory"
                label="COM_UNOFD_UNOFD_FIELD_GREETING_LABEL"
                description="COM_UNOFD_UNOFD_FIELD_GREETING_DESC"
                />
    </fieldset>
</fields>

default.php

<?php var_dump($category); ?>

output is Null

The Admin Menu works,but frontend can't get any items in that category data, is there any about develop single category view document or sample online? i tried google for solution four days,but still no idea, or the only way is get data from database? Many Thanks!

var_dump($this)will output

    object(HelloWorldViewCategory)#223 (15) { ["_name":protected]=> string(8) "category" ["_models":protected]=> array(0) { } ["_basePath":protected]=> 

string(55) "/var/www/clients/client0/web11/web/components/com_helloworld" ["_defaultModel":protected]=> NULL ["_layout":protected]=> string(7) "default" ["_layoutExt":protected]=> string(3) "php" ["_layoutTemplate":protected]=> string(1) "_" ["_path":protected]=> array(2) { ["template"]=> array(2) { [0]=>

 string(79) "/var/www/clients/client0/web11/web/templates/protostar/html/com_helloworld/category/"  bla bla bla....

Answer 1

Edit: Okay, now we have the bottom of your getOptions method(), the problem's in your view's display() method. $category is only available in the local scope of that method, you need to make it a class property.

In display() change:

$category = $this->get('Item');

to

$this->category = $this->get('Item');

In default.php:

var_dump($this->category);

Answer 2

I'd suggest you to use link to index.php?option=com_categories&extension=com_YOUREXTENSION.

And add /helpers/yourextension.php file that will generate menu by having method

public static function addSubmenu($vName)
    {
        JHtmlSidebar::addEntry(
            JText::_('COM_YOUREXTENTION_ENTRY_ONE'),
            'index.php?option=com_yourextension',
            $vName == 'entryone'
        );
        JHtmlSidebar::addEntry(
            JText::_('COM_YOUREXTENTION_ENTRY_TWO'),
            'index.php?option=com_categories&extension=com_yourextension',
            $vName == 'entrytwo'
        );
    }