define(['durandal/app'], function (app) {

    var message = ko.observable();
    var canPublish = ko.computed(function () {
        return message() ? true : false;
    });

    return {
        message: message,
        canPublish:canPublish,
        publish: function () {
            app.trigger('sample:event', message());
        }
    };
});

define(['durandal/app'], function (app) {

    return {
        received: ko.observableArray([]),
        subscription:ko.observable(),
        subscribe: function () {
            var sub = app.on('sample:event').then(function(message) {
                this.received.push(message);
            }, this);

            this.subscription(sub);
        },
        unsubscribe: function () {
            this.subscription().off();
            this.subscription(null);
        }
    };
});