After months of being gagged and leashed, iPhone developers are now free to talk about the iPhone SDK. Apple has dropped their NDA and opened the flood gates to those new developers who thirst for iPhone programming knowledge. I feel that Actionscript developers will have an easier transition to Cocoa-Touch than developers coming from other languages. Being a long time Actionscript developer myself I found it easy to port from Flash to iPhone. Further down in this article I show how I built my app in Flash and the steps I took to port it over to Cocoa. But first, here’s why I believe the learning curve is very low for Actionscript developers.

Flash and Cocoa are shockingly similar. Much of the Cocoa framework is a mirror image of Actionscript classes / components. For example:

• UIView = MovieClip
• NSNotification = Event
• UIButton = Button

Actually if you think about it, Cocoa can be seen more as the equivalent to MXML because it’s a framework. The underlying language for Cocoa is actually Objective-C. Objective-C is a lot like Actionscript except for one major difference in how methods are written and called.

In Actionscript this is how we would call a method

this.gotoPicnic();

In Objective-C methods are defined in brackets and the keyword for “this” is “self”

[self gotoPicnic];

This will be one of the biggest hurdles for many Actionscript developers to cross, especially when you start adding nested method calls inside of your method calls, for example

[self gotoPicnicWith: [self coworkersAttending]];

So what exactly is the easiest way to learn Cocoa? Well that depends on what works best for you. From my own personal experience I found that using Flash and Actionscript to develop my iPhone app made learning Cocoa very enjoyable.

Benefits of prototyping in Flash.

How to setup you flash movie.

The first thing you can do to help assist in the visual layout of your prototype is to download a free iPhone UI elements PSD. Here is a great PSD you can use for free:

http://www.tuaw.com/2008/08/24/free-library-of-iphone-ui-elements/

The iPhone’s screen size is 320 x 480, so if you are creating your app in portrait view you should set your stage size to 320 x 480, otherwise 480 x 320 for landscape view.

Converting your events in flash to work in Cocoa.

For most developers the biggest question when coming to Cocoa is “How do I use events?” My favorite part of Cocoa is its notification system. If you are familiar with PureMVC you will have no problem understanding how events work in Cocoa. In Actionscript we have “Event Dispatchers” and “Event Listeners”. The dispatchers would dispatch and event from somewhere (this.dispatchEvent(event)) and we would setup a listener to listen for that event. Also events in Actionscript have a certain type.

In Cocoa we have a little more freedom. Events are called “Notifications” and we use a “Notification Center” to handle all notifications. To give you a visual, think of the Notification Center as a bulletin board in your office that anyone can leave notes on. When someone has something to say they post a notification to the board. Anyone who is looking at the board is considered an observer (An observer is the equivalent to a listener in flash).

Lets say you (observer) is only interested in notes posted on the board that pertain to next weeks company picnic. Whenever someone comes along a puts a note on the board and its labeled “picnicNote” you will react to the note and do something… lets say you go to the picnic. You can easily have more than one observer looking for the “picnicNote” and any observer can look for many different types of notes also. So how is this coded in Cocoa?

Object1 - [[NSNotificationCenter defaultCenter] addObserver: self selector: @selector(gotoPicnic) name:@”picnicNote” object: nil]
Object2 - [[NSNotificationCenter defaultCenter] postNotificationName:@”picnicNote” object: nil]

In the above code Object1 is saying “add me to the defaultCenter and when notification named “picnicNote” is posted I want to gotoPicnic. When Object1 see’s that Object2 has posted a notification to the defaultCenter Notification board it will react by calling a method (selector) called gotoPicnic.

Using this information I was able to build my first iPhone app in Flash and port it over to iPhone. The app is “Urban Tycoon” and sold over 3000 copies in its first week. The process was pretty strait forward. Here are the steps that I took.

1. Design the UI for the app in Flash using the timeline to represent each screen.
   
2. Use Actionscript to emulate things like swipes across the screen. For example here is some code that would emulate a UIScrollView.

import flash.display.StageAlign;
import flash.display.StageScaleMode;

stage.align     = StageAlign.TOP_LEFT;
stage.scaleMode = StageScaleMode.NO_SCALE;

// holder will act as the main UIScrollView
var holder:MovieClip = new MovieClip();
addChild(holder);

holder.addEventListener(MouseEvent.MOUSE_DOWN, mapMouseDown);
holder.addEventListener(MouseEvent.MOUSE_UP, mapMouseUp);

// Start Drag on Mouse Down
function mapMouseDown(event:Event):void
{
 	holder.startDrag();
}

// Stop Drag on Mouse Up
function mapMouseUp(event:Event):void
{
 	holder.stopDrag();
}

3. After getting the basic UI functioning and some of the logic in place, export all MovieClips (that were made for the UI) as PNGs.
4. Open XCode and create a new iPhone project.
5. Inside XCode make those PNGs into UIImageViews and position them in the exact position they were in Flash.
6. Now wire up the buttons in your UI to post notifications. For example here is a button image from flash that I placed in my Xcode project. It calls a function when pressed.

   [button addTarget:self action:@selector(postPicnicNote) 
   forControlEvents:UIControlEventTouchUpInside];

   The code above adds an action to the button, it says on my TouchUpInside event call the method “postPicnicNote” on self. Remember self = this in ActionScript.

Now we have a simple iPhone app that looks and behaves like our Flash movie. Of course pushing new UIViews to the screen or adding a UIScrollView will take a little more understanding of the iPhone SDK. Apple has great documentation on it’s developer website (http://developer.apple.com).

Read more from Mike Huntington.