---
title: WWDC2001 Session 102
framework: wwdc
role: article
path: wwdc/wwdc2001-102
---

# WWDC2001 Session 102

## Transcript

Kind: captions Language: en so my name is Chuck Sula and just like everybody else here from Apple today I'm here to help you and in particular I'm here to help you learn about cocoa so let's give an idea again what cocoa is it's an advanced object-oriented framework designed from the ground up using objects and many powerful object or any methodology it provides you a full feature set for doing application development and it integrates well with other system components it's not a standalone component you can use in the POSIX API S or as you heard Scott's say earlier actually integrate with parts of carbon like the the print panels actually comes up through carbon and it's used by many important Mac os10 applications system preferences was written in Cocoa the mail application project builder let me set the stage for what you're gonna learn today my goal is to tell you what makes Cocoa unique by doing so we're gonna talk about some of the important classes in Cocoa we can't talk about all of them there's a lot and we're gonna discuss some of the main concepts and features and pick of those that make Coco unique and powerful above all I want you to learn that cocoa is powerful easy to use and can make you more productive cocoa is powerful it's an object-oriented framework designed from the ground up using objects and those object or methodologies you'll notice some of these slides are similar to earlier slides you saw today that I left for next year not to do them so early so that they can can't be reused by people before me so they're designed for extensively again like Scott said so that you the developer can make changes without a lot of effort and we use a dynamic runtime system that makes many things easy to do that you might not even consider doing with other frameworks it's easy to use because we have consistent API as of conventions again in Objective C and Java and again those of you who are not from North Objective C shouldn't be frightened it's something that it's a small extension to the ANSI C based language to support things like objects and messaging and if you're familiar with object our programming and the C based language used to build one urn in a day or two now we also have brought up this linecount thing many times so one measure of productivity is lying counts it's not the only one but it's a measure of productivity so what can Coco give you for free well in fact with no lines of code you can actually have a reasonable text setter now I know most of you are here are not in the business of writing text setters but what this means is that it this is an example of what Coco can can give you for free and the idea here is that although you're not writing text there's you want to get lots of stuff for free so that you don't have to reinvent the wheel this means you get more time to work on features which make your product unique and helps you sell your product so at this time I'd like to bring Doug Davidson up on stage he's going to show you how to write a no line text editor and sort of show off what you get for free and Coco done I'm here to show you how easy it is to get started writing great applications with Coco so we're gonna write a Coco application from scratch right now so it's fire up project builder get started this will be a cocoa document based application something along lines a simple text and all that project build will create a project for us now the main thing we get with this project is a couple of interface definition files so let's take a look at those in interface builder now the first one has a window for us where we can put the contents of our document Andy your document contents here since this is going to be a text editor what the thing that I want to put in here is a text view so I'll just drag one in off the pallet and I'll position it the way I want size it the way I want and I want it to grow when my window grows for that I have to set a couple of Springs and let's take a look at the attributes our text view might have we've already got its editable that's good multiple fonts allowed that's also good about graphics that would also be nice and undo and the other one has our main menu let's also take a look at that here's our main menu now since this is a text editor I think I would like to have a text menu font menu all right now let's see let's try building it this is always a moment of truth built that's good let's see if we can run it straight from project builder and here is our application what we get we've got a document window or maybe two or three that we can type in to let me make that a little bigger for you that's better and this has a lot of the standard text type features that you might expect like Oh copy and paste or write write a drop or maybe undo redo or bold italics underline multiple fonts or even multiple languages clinic or we can drag in inline images they make that little bigger we also have a few features that you might not expect like as you type spell checking and we also have some advanced kerning and look at your support built right in and we also have a ruler with some various formatting options and there's one more thing notice this little close button up here has a document dirty - indicator if that means that our application is automatically noticed that we edited this document if we try to close it it will ask us if we want to save changes you know bring up a say panel a little one or maybe a big one whatever we like you can try save oops didn't save the document and what's missing here we didn't write any code we forgot to add any code well at this point I have to admit that cocoa can't do absolutely everything for you you would have to write a little code to be able to open or save documents but with an additional less than twenty lines of code this text editor would be able to open and save documents in a variety of formats and we would have a full working text editor now back to you chuck all right thank you very much Doug now again the point of the demo was not to show you that you could write a text edit real easy well you can but most of you aren't going to be doing that the point was to show you that you get lots for free in cocoa and if you're like me you get like getting stuff for free like we'll Shipley was up here earlier saying you don't you know you don't enjoy writing stuff that's been done hundreds of times you want to do new unique stuff that's gonna make your product really cool okay and that's what cocoa allows you to do so let's talk about some more I guess some more realistic applications just like some of the stuff you guys are gonna be writing we have the mail application on Mac os10 who's written in about 75 thousand lines of code again you've seen this probably rehashed a couple times now but I just want to reiterate it because it's so important to understand that you get compact code size and still lots of functionality so of those 75 thousand lines of code 15,000 are actually comments so that leaves us with about sixty thousand lines of code of that 40,000 are written in reusable frameworks now this means that they're not specific to mail we're actually reusing them throughout Apple so that we write at one time and multiple applications get to use it that leaves only 20,000 lines of code for this mail application that are specific only to that mail application many of you are familiar with omni web omni web is a full-featured cocoa application it's a web browser and it was written in three hundred thousand lines of code now at first this might sound like a lot but I've been told by the omni web folks who are generous enough to give me the line counts that 120 thousand lines of code are there only to support about five various plugins like flash and so on so that leaves us what half the code only to support a couple of but you know plugins that were in C that leaves about 170,000 lines of cocoa code of that a hundred and forty thousand of them are written as reusable frameworks so even though you're noticing a theme here where typically in cocoa you're able to write your code some of it factored out into reusable frameworks now Omni actually host this on your website you can go and check out the code yourselves and they address things like networking the web HTML and some custom controls of their own so that leaves for a full-featured web browser only thirty six thousand lines of code again very compact yet full-featured okay so let's leave that's a bit of the motivation as to why you might be interested in checking out code let's talk about where cocoa fits you've seen this many times you seen at the lowest level is the cherry flavor Darwin pill love that we have maybe lime flavored graphics of quartz OpenGL and QuickTime and then like Scott talked about we have many programming environments one of which is cocoa its own tasty little component so cocoa in a little bit of detail it's it's actually divided up into two layers we have the foundation which typically non-ui classes and the app kit which are the non UI or which are the UI classes and the app contains its graphic capabilities from application service which again is quartz cook time in OpenGL cocoa is full featured there's a lot of classes here in fact there are two hundred and twenty or so classes so we don't have time to talk about all today some of you have already picked these up if you go to Hall two there's these references that you can use I guess they're cheat sheets just try and hide them conspicuously on tests so again we're not gonna have time to talk about all this today and I just want to point out what some of the stuff that we're not addressing today are Coco's again broken up into the foundation and app kit layers apke addresses things like windows and views graphics and imaging events and system interaction a number of classes for text handling which are showing off in the earlier demo then in the foundation level we have classes for basic storage and collections abstractions for dealing with file input and output for dealing with operating system mechanisms such as processes and threading and networking and communication and then some others ok so let's dive into the foundation now in detail at the root of the foundation is a class called nsobject in fact you'll notice that all classes and Coco's start with the letters NS brief history lesson this actually stands for next step because Coco was a next step technology so maybe this is a lesson for including company names your API is I don't know foundation again is below the UI level and it provides basic classes for storage and collections operating system abstractions to make dealing with the operating system easier and our core support for internationalization and localization and while I talk about the foundation I'm also going to touch on some topics or which are important at that level and in particular memory management and the concept of immutability so we have basic storage and collection classes for things like values and s strings which store unicode strings and it's data for storing a bag of bytes collections that you're typically used to from CS type classes you know arrays dictionaries and sets and what's important about these are that there have very consistent api's and they can be written to files as property lists now let me explain property lists a little bit because we've only been talking about XML in that property list Oh property lists are basically a simple object graph that we use when we write out two files and these are defined using the format is defined using XML in fact if you're interested the DTD is on the system now property list our deal is a small flexible data store for that reason has been mentioned a couple times now they're used throughout cocoa and Mac OS 10 for things like user preferences and configuration files now we also have abstractions for dealing with the operating system and I use the term abstraction a lot today and what I wanted to find what I mean by that we have it that's by extraction I mean we have a higher-level interface to gaining access to this functionality it doesn't mean that the functionality is any less powerful it just means that it's easier to use now we have abstractions for dealing with the operating system such as threads and locks for doing file input and output things like nsurl and its file handle for dealing with files we also have classes that help you do networking communication and for accessing system information now there's lots of classes and functionality here but if your needs are exceptional you can always use any system level framework or POSIX API for instance so that again Koko is not a standalone product you can use it with other components in the system internationalization is very important in Mac OS 10 obviously we're able to ship seven languages simultaneously the way we're able to do this at in the coco frameworks is through our support for Unicode data which is an NS string now those of you who are used used to using the carbene api's may have heard of CF string and a string is a very very similar class it's basically just a small shim on top of CF string so NS string stores unicode data which means it can support any language the unicode can and for that reason we use it throughout our API s instead of basically char stars now typically localizing your application involves more than just converting strings you also want to convert your images so a stop sign in the US might not make sense when you're running in some other language or some other country so you need to localize things like images and in fact your UI so NS bundle provides our support for that and this bundle is just a resource loading mechanism that knows how to rummage around in your app packaging system and find the appropriate resources for the users currently selected language it's also just a general resource loading mechanism but for localization this is what you'd use it for okay so that covers some of the basic classes and functionality and at the foundation level now I want to talk about some of the concepts that apply at the foundation level memory management is important Cocco does not use automatic garbage collection however it uses something just as simple and easy to understand it uses reference counting so the basic idea is here that when you send an object or retain message that adds a reference to the object when you send it a release that decrements the reference to an object when the reference hits zero the object will get de-allocated now the basic rules of our memory management is simple by convention only creation methods return objects that have a retain on it all other methods return objects that temporarily don't have any references if you want to keep that object around you send it to retain when you're done with it send it a release and again once it hits has no references it goes away mutability is also a very useful important concept at the foundation level many classes in the foundation are immutable classes which means that they can be modified or we have some that are immutable meaning that they can't be modified so why do we have a distinction there's a couple reasons immutable objects can't be modified which means it's safe to pass them around I can pass you in an immutable array safely if I know you can't add objects to it I might need to know that it's not changing which means I can also return immutable arrays from from my API to external clients and safely know that they won't be modified immutable classes could also have more efficient algorithms if I know an array is not going to change I might be able to do something more efficient in my implementation however the drawback of course is well it can't be modified not much used to pass around rays that you can't add things to so for that reason we also have mutable objects and for that reason lots of classes at the foundation level come in both flavors so we have NS strings and it's mutable string and in fact you'll notice the same things you know similar classes at the core foundation level mutable classes and non mutable classes so it's a concept that we throw at Mac O's time okay so that covers non UI functionality I myself am a graphics guy I love doing graphics and we're all Mac programmers here who likes to do great graphics okay everybody start okay so the app kit again is where we have our UI level layer and our graphics it provides the infrastructure for drawing and handling events and also provides many of the components that you're going to use off-the-shelf in your application we have basic controls like buttons and checkboxes advanced controls like the toolbar and we also have standard dialogues like color panel save panel open panels and we have many advanced aqua features such as drawers and transparent sheets and again as you saw earlier today Cocco features a very sophisticated text system so here's a diagram showing some of the classes that I'm going to touch on today again only about five of those 220 I'm gonna start by talking about NS application because everybody's running application so everybody has exactly one instance of NS application now this application is important because it manages the or your connection with the window server the window Center it'll set up the connection and when the window server receives events it'll dispatch them to the application who then will appropriately forward them off to whoever needs to get them and this application is also important because it allows you it gives you hooks to customizing typical application behavior so for instance if you need to customize something and do something special in an application determination there's hooks for you to customize that behavior ok everybody has an application so they got an NS application everybody also typically will have windows and a window is the guy who reserves screen real estate and provides you a place to put your topmost view and this window is also the guy who application will forward events off to and then it will figure out based on the event who needs to receive that so clicks go to the view under the mouse key events go to whichever view currently wants to receive keyboard events there's some of the magic that you heard Scott talked about we can just these keyboard events off to dine you know dynamically figure out what object wants to handle keyboard events and again and it's Windows where you'll find our support for advanced features such as drawers and transparent sheets and it's view is where you're gonna do your drawing and as view handles lots of details that you don't want to handle so some of them might you know really enjoy this stuff but typically most people don't want to worry about managing the view hierarchy worrying about coordinate system transformations view to screen transforms or worrying about clipping this all done for you and Coco also Anna's view provides basic UI functionality that you're used to having around like drag-and-drop context-sensitive menus and help tags again off the shelf there are many instances of edits view that you can just use in your applications such as and it's text view which you saw Doug use earlier or in this movie view which plays QuickTime movies and there's a number of other views now if you want to make your own view that does your own whiz-bang custom really cool drawing all you need to do is subclass and it's view and override the methods that you're interested in so if you want to draw which you're all gonna do you override draw a rect if you want to handle mouse down events you override Mouse down any other event that you want to handle you just override that method in order to handle it and it's to use where you do is where you do your drawing and Coco provides you lots of options for drawing in particular we have and it's Bezier path which allows you to do path based drawing lots of things that you're familiar with the past bate drawings such as curved a point stroke fill set a dash pattern in us image is our class that provides an abstraction over images so we support images like TIFF JPEG bitmaps anything else that you typically would expect QuickTime to support and the nice thing here is that it's an abstraction on images so we can add support for new images in fact which we have in past like PDF and your application gets that new functionality without even knowing that it existed previously we also have the ability to drawstrings the strings know how to draw themselves a class I haven't mentioned yet is NS attributed string that's our abstraction on styled text we also have abstractions for colors and fonts and again in the past we've added functionality for things like pattern colors or true typed to type fonts and we've done this without changing the API in those classes so clients have been able to pick up new functionality without having any idea that it would have existed at some point in the future and if you need to do your own graphics transforms we have NS affine transformation now there's lots of options for drawing but if your needs are exceptional you can always use quartz drawing again cocoa is not an isolated component it can be used it can use other components in the system Sony CG functions can be used at this point I like to bring it Doug back up on stage he's gonna give you a demo on how to actually cellquest Emmet's with you how to draw and how to handle events done thanks Jeff okay this time I promise we're actually going to see some code so what we're going to do right now is what might be the beginnings of an image editor perhaps we'll draw an image and we'll allow the user to click and drag to make a rectangle selection so I've already created the project for us and you're an interface builder instead of a textview I put in a custom view and set it to be my custom subclass of NS phew and back in project builder let's take a look I've added a few lines already to the implementation of my custom subclass actually just two methods for demo purposes I have hard-coded a specific image now really the only interesting line in this code so far is this one and this is an our draw rect a custom draw rect method and what this line says is that we want to draw the entire image in our entire bounds and that by itself is enough to draw the image but we also want to do the click and drive selection thing so let's add some first of all I'm going to add a couple of instance variables to keep track of where user has clicked to dragged keep track of the start point where the user started to click and the end point where they track to and next what I need to do is add just a couple of methods to keep track of those things so first of all I have my mouse down method that's going to be called automatically when the user clicks and all that this method does is to set both the start point and the end point to the location of that mouse click in our view coordinates and then we say that we need to read redisplayed and then we have another method mouse drag which will be automatically called when the user tracks and all that does is to set the end point just the end point to again to the location the mouse was dragged to in the views coordinates now given these two points it's fairly straightforward to compute the rectangle that they determine and I have a little function that does that too it's about as long as the rest of the covetous and I'm actually I'm going to insert that I don't want to go through that and the final thing we need to do is actually draw that selection rectangle so I'm going to add that to our draw rect and what this is that if the start point and end point are not the same then we set an appropriate color in this case red and create a fuzzy a path in this case the path is just a rect being the rect determined by those points and Stroke it simple enough let's see if it does let's try running it now here's our application draws the image that I've hard coded you notice again it scales nicely automatically no code needed for that and I click drag there is my selection [Applause] thank you again dougie okay so now I've talked about Anna's application and this window and ennis view and the attentive ones in the audience have noticed I've skipped one class that's everyone right and it's responder is the common superclass of all these classes I've already talked about and the reason is they all share some similar functionality in particular all honest responders can receive events and again events in KOCO arrived as methods so if you're interested in keyboard events your subclass of NS responder will override the keydown event key known method excuse me NS responder also introduces another important concept called the responder chain and every subclass of NS responder can be in this responder chain now the responder chain works like this every window knows who its first responder is every responder knows who its next responder is and so on down the line and so this forms a responder chain what will happen is when events come into the system they get dispatched typically to the first responder if it doesn't want to handle it it gets passed down the responder chain until it finds someone that wants to handle it so typically you're probably not interested in knowing about actual very low level events like mouse clicks or keydown events you're really concerned with was this button clicked or MIT was the slider manipulated things like that this is where enough's control comes into play as you can see NS control is a subclass of NS responder and NS View which means it inherits lots of functionality from these classes however NS control has some important differences and as control is defined to something that's typically triggered or activated by user action again button clicks on a button click on a button examples would be NS button and its text field or more advanced controls even like outline views now again I said it inherits lots of functionality but it also has some important differences every control has a target object in an action method I'm gonna get into this in detail in a little bit so let me just leave that for now controls also have values that can be queried so I might need to know that the sliders current value is 0.5 or that a text fields current string is something rather also since controls are typically things that I can click on I need to be able to enable them and disable them so control has support for that target action is a very important concept in cocoa and this is what makes some of that magic that Scott Forstall was talking about earlier possible the idea here is that when a control is triggered it has a target that is going to tell I was triggered so the target object is the guy that gets sent an action method in cocoa targets can be nil and when the targets nil the message will go to the first responder and again if the first responder doesn't implement that action method it goes down the chain until it finds something that wants it so this is how cut is implemented in cocoa typically when the user clicks on dragged clicks and drags down to the cut menu item we haven't actually hard-coded in a target the targets nil and so what will happen is the frontmost window its first responder will get a cut message if it doesn't actually have my cut it'll go down the chain until it finds your custom view which implements the cut message so again you can imagine how how much you know gory detail and management you'd have to do if you had to actually manage who the current target was and keep track of what windows in front we it that's all taken care of you through the beauty of the first first responder responder chain and target action at this point bring Doug Davidson back up on stage and he's going to show you how target action works in KOCO thanks Chuck so this time we're going to build on a previous example and we're going to add an action method to our custom view and to do that we're going to pay a little closer attention to scaling so I'm going to add you a little bit more code here now first of all I have one method set scale that will set the scale on our view to some float value now in cocoa every view has two rectangle parameters one is its frame which determines it in its extra in the external coordinate system and the other is its bounds which is determines its size and the internal coordinate system so to scale this view all that we're doing is setting the frame size to be the size times a scale factor and setting the bounce eyes to be our original size just a hard-coded size of the image and again saying that we need to be display and also when we get loaded we want to set the default scale to some same value one now our action method is this one called take scale frog and what that does is to set our scale based on a value determined from the sender of the action method in this case we're going to have the sender of the action method be a slider and the value of the slider is just determined by the position of the slider so the slider will tell the view what its scale should be let's take a look at our interface and interface builder now we're going to take our view and I want to group it into a scroll view so we make sure we can always see it and make this window a little bigger this thing around a bit now here I'll get a slider drag it on position it the way I want it and set some nice values for it to close from 0.5 to 1.5 and it starts at 1 now I need to hook this up here's the magical interface builder 1 to Graig saying that the target on my slider is my custom view and the method that's called this takes scale from let's see if this will build let's try our application again now you see we have our slider and the slider tells the view not a ticket scale if it's too big we can scroll around you just don't make our selection we're all set thank you very much let me show you that Doug doesn't normally program using stickies some of the beauty of what you saw here was that because again objective-c has very good introspection interface biller knew that it has these methods that it can wire together so we've talked now a lot about classes and specific functionality and although that's some of what makes par cocoa powerful it's some of the it's some of the concepts that we use in cocoa which make it really unique and powerful so I want to talk about in particular some design patterns that are used throughout cocoa in particular the notification notifications sometimes referred to as the observer pattern delegation and the model-view-controller paradigm notifications are a way to broadcast happenings throughout an application or even to other applications now those interested in knowing about happening will register as an observer typically in cocoa some of the things you can register as observers for our tell me one a window will close or tell me when a text did begin editing however you wouldn't expect notifications to be used for really low-level things like this did spin or something like that so observers have to register with somebody to say hey tell me when this event happens that guy is the notification center Notification Center is sort of the glue that makes notifications work what happens is observers register with noticing with the Notification Center telling them to name the notification they're interested in and the object that they want to monitor and also they provide a method to be called when the notification is posted now you don't actually have to tell it what object you want to monitor you can say the object I'm modern King is nil and when you do that you say I want to monitor all objects for a particular notification so I might want to know when any window in my application closed I do this by specifying nil posters are the ones who post the notification they post the name and any additional information which may be valuable for instance what windows closing delegation is a powerful design pattern that allows one object to act on behalf of another typically it's a way to provide you a way to customize an object's behavior without having to subclass so NS application has a number of delegate methods one called applications to terminate an application soap and file so if I want to customize my applications termination I provide a delegate who does some special work in applications should terminate ok so at first notification delegation somewhat sound like similar concepts and they are because you're sending messages when things happen but they have some important differences with delegation there can only be one delegate per object much like with the Highlander there can be only one however there can be many observers and because of this you'll notice that with our api's delegates typically received messages they're allowed to affect behavior because there's only one however notification observers will receive will or did type messages there's no way for you to affect it so let me give it a sort of a contrived example of making a US law in this example the house makes the law and we'll say the president's our delegate in this situation because he's allowed to veto the law when he's asked should the law pass now once the law finally passes all of us out here as notification observers learn about it through the notification law did pass it did pass we don't have any way to affect it of course there's always voting but we know sometimes that doesn't actually work in all places okay so another design pattern that we use throughout KOCO and has already been mentioned a couple times is the model-view-controller paradigm in this paradigm the model stores the data however typically it's more than just a simple data store it knows how to perform intelligent operations or business logic or things like that on the data however it's separate from the view it doesn't know any particulars about any view that it's being displayed in the view knows nothing about the data it just knows how to display typically some simple types but it's separated from the the model and the control is the guy who will tie the two together again implementing things in Model View controller is a lot of you probably familiar with will make it your application more flexible easier to port when you need to change UI classes and so on so I'm going to talk a little bit more about about it in the next couple slides and I'll usually talk about it and just call it MVC okay so I'm going to hit on a number of application level topics some which MVC effect and some which are just application level topics that you'll be interested in when you're developing your application in particular if you're writing a document sort of application Coco has a wonderful document architecture that you be interested in knowing more about every application on Mac OS 10 should have undo support and be scriptable and typically you're going to want to be able to talk to the clipboard or have preferences in your application okay document architecture it provides you a number of standard features that you want to have in an application that works with documents as you saw earlier in Doug's done we had a document based application that ran open panels and saved panels for us we didn't we didn't write any code to do that it also manages manage the document edited status again these are mundane things that you typically don't want to have to reinvent now for you to make a docking base Taplin all you're going to have to do provide routines that can load and store the data again stuff that we didn't do in the earlier demo but you provide the custom logics to do that undo is very easy to do in cocoa and for that reason every application should be undoable in fact every cocoa application as you heard before already has undo support in particular the text system has built an undo support and if you need to add your own undo support all you need to do is that when your model changes you register an undo operation with the NS undo manager and against this undo typically wants to be registered when your model changes a good separation of your model and view will make undo easy for you to implement scripting is also very easy to implement in cocoa and again that means every applications should be scriptable cocoa provides a lot for you already we handle events from the Apple script standard suite such as open print and so on the text system provides a number of the classes that you need in the text suite and if you need to add your own support for scripting which you're all gonna do you don't have to do a lot of work you have to edit a P list which again is this XML based file format and you need to write a method or two so it's very easy to do and again since scripting acts through interfaces through the model a good separation of the model and the view makes scripting easy to implement typically your application also wants to have preferences when you when you need to store preferences to disk or read them from disks you can talk to the NS user defaults object it stores preferences per user per application it also allows you to access system preferences so anything you see stored in the system prefs application you can access through NS user defaults and also if you have a suite of applications and its user defaults allows you to share preferences between them if you need to implement cut copy paste or something similar you need to talk to the clipboard or provided data right and it's pasteboard is the object that gives that functionality in particular the data can be store can be provided either immediately or in a lazy fashion and of course we all prefer to be lazy because if we have some huge data we don't want to have to compute it if it's never needed and as pasteboard also has filtering services so that you can convert to the requested format and in fact we provide conversion of mac os9 types for you automatically ok we've covered a lot of stuff today I made this thinking it might be earlier in the day I guess it's actually time to eat what I'm hoping you take from the talk today is that cocoa gives you lots of functionality you don't have to re-implement mundane tasks that aren't interesting to you and don't add value to your product you get spend time working on features which will help sell your product cocoa has lots of powerful concepts more than just the classes and the functionality of the classes we have powerful concepts that we use which make cocoa unique and powerful and again I love free stuff and cocoa gives you lots of it so it's day one and we've got a lot of sessions left if you're interested in cocoa in particular I would highly recommend going to the using cocoa talk there will be lots of code demos there we didn't show a lot today we're gonna show a lot more there the advanced cocoa talk is actually for beginners too cocoa and cocoa experience folks so everyone should feel free to attend to that and if you have feedbacks come to the feedback session on Friday there's also a couple more things you might be interested in the project builder talk coming up interface builder and learning about things such as nsurl again one of these foundation classes that I talked about there's lots of documentation on your CD the first thing I would recommend checking out if you're new to cocoa is the concepts documentation because that again is what what I think makes cocoa unique and really powerful there's lots of information elsewhere there's zero O'Reilly book that you can go grab and actually there's lots of cocoa enthusiasts out on the net that provide things like mailing lists and FAQs and free frameworks again Heather Hickman is your contact for anything cocoa there's a new cocoa development mailing list that if you're doing cocoa development you should look into subscribing you