Trigger Default values wordpress plugin on install - wordpress

Question

I spent so much time to figure this out. How do automatically fill defaults values on the field or inserted into database upon installing the plugin.
I have tried these following codes but nothing works:
register_activation_hook(__FILE__, 'just_a_handler');
function just_a_handler($plugin_options) {
$defaults = array(
'youtube_keyword' => 'keyword here',
'youtube_author' => 'author here',
'youtube_content' => 'by_keyword',
'youtube_width' => '500',
'youtube_height' => '350',
'youtube_number_of_videos' => '5',
'youtube_preview' => '',
);
$plugin_options = wp_parse_args(get_option('youtube_plugin_options'), $defaults);
}
and this one:
register_activation_hook(__FILE__, 'just_a_handler');
function just_a_handler() {
add_option("youtube_keyword", 'keyword here', '', 'yes');
add_option("youtube_author", 'author here', '', 'yes');
}

Answer 1

To automatically fill an option with some defaults you can do something like the following. Depending on when you execute this code, I think it's a good idea to check that the option doesn't already exist before filling it with the default data. Also keep in mind that if you're storing an array, you need to serialize your data before adding it to the database. Databases can only store numbers, text, and dates. Serialization takes an array and turns it into a serialized string.
function init_options() {
$retrieved_options = array();
$defaults = array(
'youtube_keyword' => 'keyword here',
'youtube_author' => 'author here',
'youtube_content' => 'by_keyword',
'youtube_width' => '500',
'youtube_height' => '350',
'youtube_number_of_videos' => '5',
'youtube_preview' => '',
);
// Check to see if the option exists
$retrieved_options = maybe_unserialize( get_option( 'youtube_plugin_options' ) );
if ( $retrieved_options == '' ) {
// There are no options set
add_option( 'youtube_plugin_options', serialize( $defaults ) );
} elseif ( count( $retrieved_options ) == 0 ) {
// All options are blank
update_option( 'youtube_plugin_options', serialize( $defaults ) );
}
}
register_activation_hook( __FILE__, 'init_options' );