How to fix Uninitialized string offset: error on a checkbox in WP Settings API

Question

I am trying to create an options page with a checkbox field. The checkbox is working fine but when I uncheck it and save settings, an error string shows on

Notice: Uninitialized string offset: 0 in C:\xampp\htdocs\project\wp-content\plugins\test\admin\options.php on line 55

Here is the main settings code:

register_setting('twb_settings', 'twb_option', '' );

add_settings_section('twb_section', 'General Settings', '', __FILE__);

add_settings_field(  'hide_avatar',  'Hide Avatar',  'hide_vatar_fn',  __FILE__,  'twb_section');

function hide_vatar_fn()
{
    $options = get_option( 'twb_option' );      
    echo'<input type="checkbox" id="hide_avatar" name="twb_option[hide_avatar]" value="1" ' . checked(1, $options['hide_avatar'], false) . '/>';
}

If I add a sanitization call back in register_settings, then the error get replace with Undefined Variable error.

If I deactivate WP_Debug mode, all errors are gone.

Answer 1

Most likely your $options is a string and not an array.

It is always better to validate that the $options are in the format you are expecting especially in development time when you are likely to switch formats and too lazy to clean the DB when doing that.

something like

if (!isset($options['hide_avatar'])) 
  $options['hide_avatar'] = 0;

Might have still resulted in a strange error, but it would have been little more easier to understand exactly where and maybe why.