How to set and get values in multiselect in admin form. Magento 1.9

Question

I want to create one multi-selector on the form to select multiple categories.

I have created a field set for that but how can I display values into that to select multiple categories.

this is my fieldset

   $fieldset->addField("visible_in", "multiselect", array(
            "label" => Mage::helper("slider")->__("Visible In"),
            "name" => "visible-in",
            'values'    => 'hello',
            'required' => true,
        ));

Currently multiselector showing blank

how to add values into it and where to create the function for it?

Answer 1

In Field Call Your Block :-

 $fieldset->addField("visible_in", "multiselect", array(
                "label" => Mage::helper("slider")->__("Visible In"),
                "name" => "visible-in",
                'values'    => Mage::getModel('vendor_module/cms_block_blocks')->getBlockOptions(),
                'required' => true,
            ));

app/code/local/Vendor/Module/Model/Cms/Block/Blocks.php :-

<?php

class Vendor_Module_Model_Cms_Block_Blocks {

    public function getBlockOptions() {

        foreach($cmsBlocks as $block){
            $output[] = array(
                'value' => 'pass value',
                'label' => 'pass label'
                );
          }

        return $output;
    }
}

Answer 2

You need to set the field for multi-select as

 $fieldset->addField("visible_in", "multiselect", array(
        "label" => Mage::helper("slider")->__("Visible In"),
        "name" => "visible-in",
        'values'    => $this->getOptionArray(),
        'required' => true,
    ));

In this Most important value, here we are calling the function to select categories

'values' => $this->getOptionArray(),

In the same file write this code

    const REPEATER = '_';
    const PREFIX_END = '';
    protected $_options = array();

 public function getOptionArray($parentId = 1, $recursionLevel = 3)
    {
        $recursionLevel = (int)$recursionLevel;
        $parentId       = (int)$parentId;
        $category = Mage::getModel('catalog/category');
        /* @var $category Mage_Catalog_Model_Category */
        $storeCategories = $category->getCategories($parentId, $recursionLevel, TRUE, FALSE, TRUE);
        foreach ($storeCategories as $node) {
            /* @var $node Varien_Data_Tree_Node */
            $this->_options[] = array(
                'label' => $node->getName(),
                'value' => $node->getEntityId()
            );
            if ($node->hasChildren()) {
                $this->_getChildOptions($node->getChildren());
            }
        }
        return $this->_options;
    }
    /**
     * @param Varien_Data_Tree_Node_Collection $nodeCollection
     */
    protected function _getChildOptions(Varien_Data_Tree_Node_Collection $nodeCollection)
    {
        foreach ($nodeCollection as $node) {
            /* @var $node Varien_Data_Tree_Node */
            $prefix = str_repeat(self::REPEATER, $node->getLevel() * 1) . self::PREFIX_END;
            $this->_options[] = array(
                'label' => $prefix . $node->getName(),
                'value' => $node->getEntityId()
            );
            if ($node->hasChildren()) {
                $this->_getChildOptions($node->getChildren());
            }
        }
    }

The output for this is as

This worked for me. Thanks.