Meta Box

Hi,

Yes, I can call the function and it will return the options, but in your example it's a simple function that doesn't take time to execute. And it is not used as a callback, because I have to call it manually.

Now, say that my_func9999 function runs queries against the database, requests some data from third party services, etc., and takes a second or more to execute. Then each time I declare that field, it will slow down the request.
So the only option I have currently is to avoid declaring that field and wrap the declaration with a condition check, like

add_filter( 'rwmb_meta_boxes', 'your_prefix_function_name' );
function your_prefix_function_name( $meta_boxes ) {
    if( $i_really_need_this_field_during_this_request ) {
        $meta_boxes[] = [
            'title'  => __( 'My Custom Fields', 'your-text-domain' ),
            'id'     => 'my-custom-fields',
            'fields' => [
                [
                    'type'          => 'select_advanced',
                    'name'          => esc_html__( 'Supervisor', 'apms' ),
                    'id'            => 'supervisor_id',
                    'options'       => my_func9999(),
                    'required'      => true,
                    'js_options'    => [
                        'placeholder' => esc_html__( 'Choose Supervisor', 'apms' ),
                    ],
                    'admin_columns' => true
                ]
            ],
        ];
    }
    return $meta_boxes;
}

It is hard to determine if $i_really_need_this_field_during_this_request is true or false.
So this can be solved if the plugin allows to pass the my_func9999 function as a callback, and not call it directly during the declaration, like

function your_prefix_function_name( $meta_boxes ) {
    $meta_boxes[] = [
        'title'  => __( 'My Custom Fields', 'your-text-domain' ),
        'id'     => 'my-custom-fields',
        'fields' => [
            [
                'type'          => 'select_advanced',
                'name'          => esc_html__( 'Supervisor', 'apms' ),
                'id'            => 'supervisor_id',

// I'm passing this function as a callback, instead of calling it directly,
// so only when the plugin needs the options, it can call the callback function itself and get the options
                'options'       => 'my_func9999',

                'required'      => true,
                'js_options'    => [
                    'placeholder' => esc_html__( 'Choose Supervisor', 'apms' ),
                ],
                'admin_columns' => true
            ]
        ],
    ];
    return $meta_boxes;
}

Or plugin can provide a filter to get the options like

function your_prefix_function_name( $meta_boxes ) {
    $meta_boxes[] = [
        'title'  => __( 'My Custom Fields', 'your-text-domain' ),
        'id'     => 'my-custom-fields',
        'fields' => [
            [
                'type'          => 'select_advanced',
                'name'          => esc_html__( 'Supervisor', 'apms' ),
                'id'            => 'supervisor_id',

// I'm not passing any option, I'll use a filter hook to provide the options later
                'options'       => array(),

                'required'      => true,
                'js_options'    => [
                    'placeholder' => esc_html__( 'Choose Supervisor', 'apms' ),
                ],
                'admin_columns' => true
            ]
        ],
    ];
    return $meta_boxes;
}

add_filter( 'rwmb_meta_boxes_get_options', 'my_func9999_v2', 10, 3 );
function my_func9999_v2( $options, $box_id, $field_id ) {
    if( 'my-custom-fields' === $box_id && 'supervisor_id' === $field_id ) {
        $options['a'] = 'A';
        $options[1] = 1;
        $options[2] = 2;
        $options['b'] = 'B';
    }

    return $options;
}

So when the plugin needs the options, for example when it is going to draw the dropdown, it can call the callback function, or it can run apply_filters to get the options.

I know that the plugin doesn't support passing callbacks and it doesn't filter the options either, but it would be great if it could do that, it would free the developers from writing a lot of messy conditions and it will work much more faster.

Hope it makes sense.
Thank's a lot.