Making update notice functionality for my themes - wordpress

Question

I've created one of my themes.I want to add update functionality through api
The notice should be visible when I use the theme, if required for theme update
Actually i have no idea so please give me your suggestion or give me a code,so i can add functionality for update theme.
Note : If you have a no idea for api so you can provide another code

Answer 1

You can use site_transient_update_themes here:
add_filter ( 'site_transient_update_themes', 'theme_check_for_update' );
function theme_check_for_update ( $transient ) {
// Check Theme is active or not.
if( empty( $transient->checked['Your-Theme-Name'] ) )
return $transient;
$request = theme_fetch_data_of_latest_version();
if ( is_wp_error( $request ) || wp_remote_retrieve_response_code( $request ) != 200 ) {
return $transient;
} else {
$response = wp_remote_retrieve_body( $request );
}
$data = json_decode( $response );
if ( version_compare( $transient->checked['Your-Theme-Name'], $data->new_version, '<' ) ) {
$transient->response['Your-Theme-Name'] = (array) $data;
add_action('admin_notices', 'theme_update_admin_notice');
}
return $transient;
}
function theme_fetch_data_of_latest_version() {
// Your API call to check for new version
$request = wp_safe_remote_get( 'https://yourdomain.com/api/upgrade-json/' );
/*
Response Shoul be in following format:
{
"new_version": "1.0.4",
"url": "https://yourdomain.com/theme/changelog/",
"package": "https://yourdomain.com/theme/theme.zip"
}
*/
return $request;
}
function theme_update_admin_notice(){
echo '<div class="notice notice-warning notice-alt is-dismissible">
<p>New Theme Update is available.</p>
</div>';
}