sap.ui.define([
   "sap/m/MessageBox",
   "sap/ui/core/mvc/Controller"
], function (MessageBox, Controller) {
   "use strict";

   return Controller.extend("your.namespace.controller.App", {
      onInit: function () {
         // Initialization code here
      },

      onShowAlert: function () {
         MessageBox.alert("This is a Fiori alert!");
      }
   });
});