Hjdcti

I have created custom CRUD on new database table. I just wanted to save comma separated categories in a field.

I have this code for multiselect categories:

$fieldset->addField(
 'categories',
 'multiselect',
 [
 'label' => __('Categories'),
 'title' => __('Categories'),
 'name' => 'categories',
 'values' => VendorModuleBlockAdminhtmlProductsGrid::getCategories(),
 'note' => __('Could be multiple'),
 'disabled' => $isElementDisabled
 ]
);

I have created getCategories function in Grid.php.

Can anyone suggested how to populate categories in tree form and return categories array

After so many tries, I have figured out the solution for my own question.

I used this code to make multiselect (as mentioned in my question):

$fieldset->addField(
 'categories',
 'multiselect',
 [
 'label' => __('Categories'),
 'title' => __('Categories'),
 'name' => 'categories',
 'values' => VendorModuleBlockAdminhtmlProductsGrid::getCategories(),
 'note' => __('Could be multiple'),
 'disabled' => $isElementDisabled
 ]
);

In Grid.php file I have created two functions
one is to create simple array for multi select values:

static public function getCategories()

 $data_array = array();
 foreach (VendorModuleBlockAdminhtmlProductsgridGrid::getCategoryTree() as $k => $v) 
 $data_array[] = array('value' => $k, 'label' => $v);
 
 return ($data_array);

And the 2nd one is a recursive function to generate category tree

static public function getCategoryTree($categories = "", $data_array = array())

 if(empty($categories)) 
 $_objectManager = MagentoFrameworkAppObjectManager::getInstance();
 $categoryFactory = $_objectManager->create('MagentoCatalogModelResourceModelCategoryCollectionFactory');
 $categories = $categoryFactory->create()
 ->addAttributeToSelect('*')//or you can just add some attributes
 ->addAttributeToFilter('level', 2)//2 is actually the first level
 ->addAttributeToFilter('is_active', 1)//if you want only active categories
 ->addAttributeToSort('position', 'ASC');
 

 foreach($categories as $k=>$category)
 $level = $category->getLevel();
 $data_array[$category->getId()] = str_repeat("*",$level)." ".$category->getName();
 $childCategories = $category->getChildrenCategories();
 if(count($childCategories) > 0)
 $data_array = VendorModuleBlockAdminhtmlProductsgridGrid::getCategoryTree($childCategories, $data_array);
 
 
 if(count($data_array) == 0)
 return $data_array;
 
 return ($data_array);

My final array $data_array contains the IDs in array key and Category title in values.