I added this code for **Multi Select** in my **form**.

File Path Should be like: `app\code\Vendor\Module\Block\Adminhtml\Mpages\Edit\Tab\Main.php`

    $fieldset->addField(
                'categories',
                'multiselect',
                [
                    'label' => __('Categories'),
                    'title' => __('Categories'),
                    'name' => 'categories',
    				'required' => true,
                    'options' => \Vendor\Module\Block\Adminhtml\Mpages\Grid::getValueArray7(),
                    'disabled' => $isElementDisabled
                ]
            );

This is my `getValueArray7()` function in grid file.

    static public function getValueArray7()
    		{
                $data_array=array();
    			foreach(\Vendor\Module\Block\Adminhtml\Mpages\Grid::getOptionArray7() as $k=>$v){
                   $data_array[]=array('value'=>$k,'label'=>$v);		
    			}
                return($data_array);
    
    		}

It shows me empty multi select field.