Migration from OWF Eventing to IWC Data API

This tutorial is for developers who are migrating applications previously developed for the Ozone Widget Framework (OWF) to use IWC. This tutorial has the following prerequisites:

1. Setup and Key Terms
2. Using References
3. Basic Data Sharing

Overview

This tutorial covers:

1. OWF.Eventing.publish functionality migration
2. OWF.Eventing.subscribe functionality migration
3. Recreating the Announcing Clock and Second Tracker from the OWF7 Developer Guides.

As covered in the (OWF) Application Setup guide, OWF application logic runs inside of a OWF.ready callback. This guide focuses on logic running within said callback.

Publish

In OWF, publishing data required a channel and some payload.

OWF

var currentTimeString = "The time is: " + Date.now();
OWF.Eventing.publish("ClockChannel", currentTimeString);

In IWC, calling a set action on a reference to a Data API resource replicates the publish functionality.

IWC

var clockRef = new iwc.data.Reference("/ClockChannel");

var currentTimeString = "The time is: " + Date.now();
clockRef.set(currentTimeString);

Note: The set functionality causes the last payload set to a resource (channel) to be stored in the Data API. The set functionality modifies the state of the resource rather than just broadcasting on a channel.

Subscribe

In OWF, listening to published data on a channel used the subscribe action. It took a channel and some callback function.

OWF

var callback = function(sender, msg){
  console.log("Received: ", msg);
};

OWF.Eventing.subscribe("ClockChannel", currentTimeString);

In IWC, calling a watch action on a reference to a Data API resource (channel) and with a supplied callback replicates this functionality.

IWC

var clockRef = new iwc.data.Reference("/ClockChannel");

var callback = function (change, done) {
  console.log("New Value: ", change.newValue);
};

clockRef.watch(callback);

Response Format differences

Unlike the OWF callback, which receives the sender and message, the IWC callback receives the new and oldvalue of the watched resource. object sent to the client.

• change: The message payload, structured for a watch
• change.newValue: The new value (payload) of the resource
• change.oldValue: The previous value (payload) of the resource
• change.deleted: A boolean flag marking if the resource was destroyed

Watch also calls Get

Unlike OWF subscribes, an IWC watch callback is triggered when the state of the resource changes rather than a message broadcast received. This means if the resource is deleted, the watcher gets notified.

As with all IWC actions, the watch action's promise will resolve when the request was handled. As covered in the Basic Data Sharing tutorial, the watch action will resolve with the value of the resource. This means when registering a watch on a resource, if it has a value it is gathered instantly, preventing the application from waiting for a change in value:

IWC

var clockRef = new iwc.data.Reference("/ClockChannel");

var callback = function (change, done) {
  console.log("New Value: ", change.newValue);
};
var onResolved = function(value){
  console.log("Initial receive: ", value);
};

clockRef.watch(callback).then(onResolved);

Recreating Announcing Clock and Second Tracker

This is a rewrite of the example widgets in the OWF7 Developer Guides. Some of the code has been simplified to better showcase the IWC changes (clock string generation). Note, the Connection Uptime in the Second Tracker is actually a receive count.

Second Tracker

Announcing Clock