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WatchKit Apps & Sending Data From Apple Watch To iPhone

Since the launch of WatchKit in November 2014, I have been doing research and development for the Apple Watch.

In this post, I’ll be offering some insight based on my experience building an app using the WatchKit SDK. We will cover the structure of a Watch application, information about interfacing, and a method of connecting a Watch App to its iOS counterpart.

WatchKit Apps

A Watch app split into two parts: a WatchKit App containing the storyboard and resources which is installed on the Watch device, and a WatchKit Extension containing all of the code and other supporting files. With this configuration, when an app is launched on the Watch, the Watchkit Extension runs on the iPhone in the background. The WatchKit App and the WatchKit Extension work hand-in-hand and function as a single app for the Watch.


Watch apps exist as children of regular iPhone apps. A Watch app is intended to complement its iPhone counterpart and they both will exist as a part of the same Xcode project. Despite this, the WatchKit and iPhone apps run independently of each other.


In order to send data from the Apple Watch to the iPhone, we need a way of communicating from the Watch app to the iPhone app.

The WatchKit Interface

Managing layouts for views with WatchKit is done in a way that is familiar to iOS developers, using a storyboard and controllers. Watch Apps contain a storyboard file called “Interface” and the WatchKit Extension contains WKInterfaceController classes. These files work as WatchKit’s version of the Main.storyboard and UIViewController classes for iOS.


WatchKit Interface Controllers work very similarly to View Controllers – for example, they can have bound IBOutlets and IBActions for objects in the storyboard.


The main difference lies within the interface layouts in the storyboards. When interface objects such as Tables, Buttons, or Labels are dragged into an interface layout, instead of being placed wherever it was dragged to and defaulting to no constraints, the object will snap into place filling the width of the layout with a fixed height.


With some experimentation, I quickly learned that there isn’t much versatility in the layout design. In my time messing around in Xcode, I found that each element of my layouts needs to be adequately spaced to be easily readable by the user. WatchKit’s storyboard seems to encourage developers to abide by Apple’s guidelines for Watch Apps, which emphasize that these layouts should be made to be simplistic and readable. Also mentioned in Apple’s guidelines are the navigation schemes that interfaces must follow: Page based or Hierarchical.



Read more information about this on the Apple Watch Programming Guide.

Code Example: Sending data to iPhone

As a part of my research and development, I’ve been working on an app for the popular social website, reddit, which essentially involves showing a feed of information on the Watch. Over the course of developing this app, I discovered how the pairing of the iPhone and the Apple Watch has the potential to be useful. In this case, tapping on a button on the Watch app will open the link on the iPhone, where you can interact on a larger screen and take many more actions.

To make a simple demo of this functionality, place a button on the WatchKit interface and a label on the iOS app’s storyboard.


Now, hook up the button to the WatchKit Interface Controller as an IBAction in order to respond to button tap events. Also hook up the Label to the UI View Controller as an IBOutlet.


In the Interface Controller, we make up a string variable to send to the label.


In the button’s IBAction method, make a dictionary that includes the string variable you made. This dictionary is what is passed to the iPhone app:


Use the following method to send the dictionary to the iPhone:


In the AppDelegate of the iOS app, add the following application method. This is what will handle the previous methods communication from the Watch:


A notification can be used to notify a view controller that data has been received and to pass it along:


Finally in the view controller, make a listener for the notification that will update the label’s text to the string that was sent with the data:


To run this demo, be sure to first build both the iOS and Watch Apps. Run the Watch app from Xcode and launch the iOS app from the iOS Simulator. Tap the button on the Watch to see the text on the label update on the iPhone.


See example code on GitHub.

The reddit watch app I built based on this is featured in this demo video:

For the complete code see this GitHub link:


Ultimately, while the pairing of the iPhone and the Apple Watch highlights the idea that the Apple Watch is a mere “second display” for the iPhone, in actuality, it can pose benefits to users. People will tend to use their Apple Watch to quickly check on information that is immediately relevant like notifications or weather. If more action is required from the user to browse as site, for example, it may be beneficial to refer the user to the parent iPhone app from the Watch, as demonstrated in this guide.

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Appcelerator Titanium SNMP module is now open sourced

We recently open sourced the nf_snmp Titanium module, and have released the code on Github.

Quick example of how to use this

var snmpModule = require("netfunctional.snmp");

var snmp = snmpModule.createSNMPClient({
hostname : hostaddress,
community : "public",
mib : 'system.sysUpTime.0',
time_out : 50000 // 5 seconds

var result = snmp.fetch();

if(result == null) {
return null;
} else {
var temp = result.split(" ");
var tmp2 = '';
for(var i = 3; i < temp.length; i++) { tmp2 += temp[i] + " "; } return _callback(hostaddress, tmp2); }

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Redeeming App Promotion Codes

As part of app marketing and release processes, we frequently use Apples iTunes promo codes or redemption codes – the seemingly random string of characters issued by the iTunes store.

We’ve put together a quick doc for our customers on how to redeem these codes, using either the App Store on the device, or iTunes – you can download it from here: How To Redeem Promo Codes

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Enabling SNMP on VMWare ESX + ESXi

ESX 4.x
VMWare supports SNMP on ESX through the use of the net-snmp agent – see VMWare’s SNMP on 4.x docs for details. An example snmp.conf file:

syscontact [email protected]
syslocation Datacenter, Rack 32, U2
rocommunity public
proxy -v 1 -c public udp: .
proxy -v 2c -c public udp: .

ESXi 4.x

Matthew White has written a quick and to the point article on enabling SNMP on ESXi – you can read it on his blog.

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Enabling SNMP on Cisco Routers

Our SNMP Scan App searches for SNMP enabled devices. This usually finds printers, home routers and other networked devices. By default, however, Cisco IOS devices won’t be found, and can’t be graphed. This is because Cisco IOS disables SNMP by default.

Here’s to safely enable it.

  1. Login to your router, switch or access point.
  2. Enter configuration mode (config term)
  3. Setup an access list on which network you will allow SNMP requests to come from. In our example, we’ll use the network. So we enter
    access-list 30 permit
  4. Enable SNMP – pick your community name. In our example, we’ll use ‘netfunctional’ as the community name.
    snmp-server community netfunctional RO 30

    This lets any device which matches Access List 30 talk to our Cisco device using the SNMP community ‘netfunctional’.

  5. Exit configuration mode – enter
  6. Save the configuration – enter
    write memory

Note that these instructions will likely work for Juniper, Foundry Networks and other devices which use Cisco IOS-like syntax for configuration. For more information, see Cisco’s Cisco IOS Configuration – SNMP Chapter.

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Obtaining Promo Codes (iOS)

Our customers often ask us how to go about getting promo codes for their apps. These need to be requested by the iTunes account holder, not a regular development account. The steps are simple:

  1. Log into the iTunes Connect account as a team leader
  2. From the main page select “Manage Your Applications”
  3. Select the app icon of the app to generate promo codes for
  4. On the current version of the app select  “View Details”
  5. Select the “Promo Codes” blue bar in the top right
  6. Enter the number of codes you wish to generate.  Only request what you need since there is a 50 limit for every release of the app.
  7. If you want to view previously issued codes select the “View History” button in the top left

  8. Accept the terms and agreements
  9. Download the text file with the codes
  10. Distribute codes to users

Note: Codes only last for 4 weeks (28 days) so don’t just request all 50 at once.

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