define ( 'MY_PLUGIN_VERSION', '2.0.0');

register_activation_hook(__FILE__, 'my_plugin_activation'));
register_deactivation_hook(__FILE__, 'my_plugin_deactivation'));
function my_plugin_activation() {
// Initialize some stuff for my_plugin
}
function my_plugin_deactivation() {
// Welp, I've been deactivated - are there some things I should clean up?
}

function my_plugin_activation() {
$version = get_option( 'my_plugin_version' );

if( version_compare($version, '2.0.0', '<')) {
    // Do some special things when we update to 2.0.0.
}

update_option( 'my_plugin_version', MY_PLUGIN_VERSION );
return MY_PLUGIN_VERSION;
}

function my_plugin_is_current_version(){
    $version = get_option( 'my_plugin_version' );
    return version_compare($version, MY_PLUGIN_VERSION, '=') ? true : false;
}

if ( !my_plugin_is_current_version() ) my_plugin_activation();

add_action('activated_plugin', 'my_plugin_activation_error');
my_plugin_activation_error() {
    file_put_contents( plugin_dir_path(__FILE__) . '/error_activation.html', ob_get_contents());
}