Magento 2: How add dropdown in admin form?

Question

I have set dropdown in form.xml like

<argument name="data" xsi:type="array">
    <item name="options" xsi:type="string">Book\Flip\Model\Category\Attribute\Source\Category</item>
    <item name="config" xsi:type="array">
        <item name="dataType" xsi:type="string">text</item>
        <item name="label" translate="true" xsi:type="string">category</item>
        <item name="formElement" xsi:type="string">select</item>
        <item name="source" xsi:type="string">flip</item>
        <item name="sortOrder" xsi:type="number">20</item>
        <item name="dataScope" xsi:type="string">category</item>
        <item name="validation" xsi:type="array">
            <item name="required-entry" xsi:type="boolean">false</item>
        </item>
    </item>
</argument>

and create model

namespace Book\Flip\Model\Category\Attribute\Source;

    class Category extends \Magento\Eav\Model\Entity\Attribute\Source\AbstractSource
    {
        protected $_optionsData;

        public function __construct(array $options)
        {
            $this->_optionsData = $options;
        }

        public function getAllOptions()
        {
            if ($this->_options === null) {
                $this->_options = [
                    ['value' => '1', 'label' => __('science')]
                ];
            }
            return $this->_options;
        }
    }

But in admin form it's shown a blank dropdown.

Answer 1

Change Category class by following code:

namespace Book\Flip\Model\Source;

class Category implements \Magento\Framework\Option\ArrayInterface
{
    /**
     * Retrieve options array.
     *
     * @return array
     */
    public function toOptionArray()
    {
        $result = [];

        foreach (self::getOptionArray() as $index => $value) {
            $result[] = ['value' => $index, 'label' => $value];
        }

        return $result;
    }

    /**
     * Retrieve option array
     *
     * @return string[]
     */
    public static function getOptionArray()
    {
        return [1 => __('science')];
    }

    /**
     * Retrieve option array with empty value
     *
     * @return string[]
     */
    public function getAllOptions()
    {
        $result = [];

        foreach (self::getOptionArray() as $index => $value) {
            $result[] = ['value' => $index, 'label' => $value];
        }

        return $result;
    }

    /**
     * Retrieve option text by option value
     *
     * @param string $optionId
     * @return string
     */
    public function getOptionText($optionId)
    {
        $options = self::getOptionArray();

        return isset($options[$optionId]) ? $options[$optionId] : null;
    }
}

Answer 2

I assume you found this out by now, but the xml in the form ui

<item name="options" xsi:type="string">Book\Flip\Model\Category\Attribute\Source\Category</item>

belongs under data as a sibling of config not a child, and its xsi:type should be "object"

Like this

<argument name="data" xsi:type="array">
    <item name="options" xsi:type="object">Book\Flip\Model\Category\Attribute\Source\Category</item>
    <item name="config" xsi:type="array">
        <item name="dataType" xsi:type="string">text</item>
        <item name="label" translate="true" xsi:type="string">category</item>
        ...

I also was stuck on this issue for awhile until I figured out that bit.

Answer 3

class category implements \Magento\Framework\Option\ArrayInterface
{ 
    //Below function is supposed to return options.
    public function toOptionArray()
    {
        return [
            ['value' => 1, 'label' => 'label1'],
            ['value' => 2, 'label' => 'label2']
        ];
    }
}

Answer 4

If you need to add an extra select field to an already existing form not built with ui-components and if you need to apply to that field a custom model config source you can use this code:

         $fieldset->addField(
            'x_custom_slideshow',
            'select',
            [
                'name' => 'brand_custom_slideshow',
                'label' => __('Choose slideshow'),
                'title' => __('Choose slideshow'),
                'required' => false,
                'values' => $sliderConfig->toOptionArray()
            ]
        );

after you previuosly specified/loaded the model config class via contructor or via object manager for eg.

$sliderConfig = \Magento\Framework\App\ObjectManager::getInstance()->get('Namespace\Slideshow\Model\Config\Source\Slideshow');

I hope this helps.