How to create a service inside a custom widget?

I am trying to develop a print widget extension, allowing to print an HTML including a QR code or an image. For that, I need a service called "Print" in my custom widget.

I tried to add the "widgetServices" function in the *.ide.js file:

    this.widgetServices = function () {
    return {
            'Print': { 'warnIfNotBound': false }
        };
    }

In the *.runtime.js file, I added the function "serviceInvoked":

this.serviceInvoked = function (serviceName) {
        if (serviceName === 'Print') {
        printJS('div-to-print', 'html');
        thisWidget.jqElement.triggerHandler('PrintFinished');
        } else {
            TW.log.error('Print widget, unexpected serviceName invoked "' + serviceName + '"');
        }
    };

I join the IDE and RUNTIME JavaScript files, so you can see my whole code.

When I import it in the composer, I can bind an event to the service "Print". However, when I view the mashup, the service is never called. Does someone know how to fix that issue?

Thanks,

Antoine