Scott Leberknight's Weblog

Last week while doing the usual (web development stuff) I discovered a few Firefox extensions I didn't even know I was missing until I found them by accident. The "accident" happened while adding Firebug to a Firefox that was running in a VMWare Fusion Windows virtual machine on which I was testing in, gasp, Windows. I went to find add-ons and searched for Firebug. And up came not only Firebug but also results for Firecookie, Firefinder, Inline Code Finder for Firebug, and CodeBurner for Firebug.

Of course everyone doing web development uses Firebug (or really should anyway) since it rules. But these other extensions provide some really nice functionality and complement Firebug perfectly. Here's a quick run down:

Firecookie

Firecookie lets you see all the cookies for a site, add new ones, remove existing cookies, etc. It gives useful information about each cookie like the name, value, raw value (if URI-encoded), domain, size, path, expiration, and security. Very cool.

Firefinder

Firefinder for Firebug lets you search for elements on a page using either CSS expressions or an XPath query. In the list of matching elements, you can expand each result, inspect the element by clicking the "Inspect" link, or click "FriendlyFire" which will copy the content you're looking at and post it up to JS Bin. (Be careful with this one if you have code you'd rather not have going up over the wire to a different web site.) Firefinder also puts a dashed border around each matching element it found. As you hover over search results, it highlights the matching element in the page. This is really useful when you want to find all elements matching a CSS expression or when you'd like to use XPath to find specific elements. Nice.

Inline Code Finder for Firebug

The Inline Code Finder does just that. It finds inline CSS styles, JavaScript links, and inline events, and reports the number of each of these in its results pane. Even better, it highlights each of these problems on the page you are viewing with a thick red border, and as you hover over them it shows you what the problem is in a nicely tooltip. This is really nice to help you become less obtrusive by writing more unobtrusive JavaScript and avoiding inline styles. For older sites or sites that weren't designed with "unobtrusivity" in mind though, be warned that there might be a lot of red on the page!

CodeBurner for Firebug

CodeBurner for Firebug provides an inline HTML and CSS reference within Firebug. It allows you to search for HTML elements or CSS styles and shows a definition and an example. It also provides links to the awesome Sitepoint reference and even to the Sitepoint live demos of the feature you are learning about. This is so unbelievably useful to have a HTML and CSS references directly within Firebug it isn't even funny. Thanks Sitepoint.

When you have collections of associated objects in domain objects, you generally want to specify some kind of default sort order. For example, suppose I have domain objects Timeline and Event:

@Entity
class Timeline {

    @Required 
    String description

    @OneToMany(mappedBy = "timeline")
    @javax.persistence.OrderBy("startYear, endYear")
    Set<Event> events
}

@Entity
class Event {

    @Required
    Integer startYear

    Integer endYear

    @Required
    String description

    @ManyToOne
    Timeline timeline
}

In the above example I've used the standard JPA (Java Persistence API) @OrderBy annotation which allows you to specify the order of a collection of objects via object properties, in this example a @OneToMany association . I'm ordering first by startYear in ascending order and then by endYear, also in ascending order. This is all well and good, but note that I've specified that only the start year is required. (The @Required annotation is a custom Hibernate Validator annotation which does exactly what you would expect.) How are the events ordered when you have several events that start in the same year but some of them have no end year? The answer is that it depends on how your database sorts null values by default. Under Oracle 10g nulls will come last. For example if two events both start in 2001 and one of them has no end year, here is how they are ordered:

2001 2002  Some event
2001 2003  Other event
2001       Event with no end year

What if you want to control how null values are ordered so they come first rather than last? In Hibernate there are several ways you could do this. First, you could use the Hibernate-specific @Sort annotation to perform in-memory (i.e. not in the database) sorting, using natural sorting or sorting using a Comparator you supply. For example, assume I have an EventComparator helper class that implements Comparator. I could change Timeline's collection of events to look like this:

@OneToMany(mappedBy = "timeline")
@org.hibernate.annotations.Sort(type = SortType.COMPARATOR, comparator = EventCompator)
 Set<Event> events

Using @Sort will perform sorting in-memory once the collection has been retrieved from the database. While you can certainly do this and implement arbitrarily complex sorting logic, it's probably better to sort in the database when you can. So we now need to turn to Hibernate's @OrderBy annotation, which lets you specify a SQL fragment describing how to perform the sort. For example, you can change the events mapping to :

@OneToMany(mappedBy = "timeline")
@org.hibernate.annotations.OrderBy("start_year, end_year")
 Set<Event> events

This sort order is the same as using the JPA @OrderBy with "startYear, endYear" sort order. But since you write actual SQL in Hibernate's @OrderBy you can take advantage of whatever features your database has, at the possible expense of portability across databases. As an example, Oracle 10g supports using a syntax like "order by start_year, end_year nulls first" to order null end years before non-null end years. You could also say "order by start_year, end year nulls last" which sorts null end years last as you would expect. This syntax is probably not portable, so another trick you can use is the NVL function, which is supported in a bunch of databases. You can rewrite Timeline's collection of events like so:

@OneToMany(mappedBy = "timeline")
@org.hibernate.annotations.OrderBy("start_year, nvl(end_year , start_year)")
 Set<Event> events

The expression "nvl(end_year , start_year)" simply says to use end_year as the sort value if it is not null, and start_year if it is null. So for sorting purposes you end up treating end_year as the same as the start_year if end_year is null. In the contrived example earlier, applying the nvl-based sort using Hibernate's @OrderBy to specify SQL sorting criteria, you now end with the events sorted like this:

2001       Event with no end year
2001 2002  Some event
2001 2003  Other event

Which is what you wanted in the first place. So if you need more complex sorting logic than what you can get out of the standard JPA @javax.persistence.OrderBy, try one of the Hibernate sorting options, either @org.hibernate.annotations.Sort or @org.hibernate.annotations.OrderBy. Adding a SQL fragment into your domain class isn't necessarily the most elegant thing in the world, but it might be the most pragmatic thing.

Last week I tweeted about groovification, which is defined thusly:

groovification. noun. the process of converting java source code into groovy source code (usually done to make development more fun)

On my main day-to-day project, we've been writing unit tests in Groovy for quite a while now, and recently we decided to start implementing new code in Groovy rather than Java. The reason for doing this is to gain more flexibility in development, to make testing easier (i.e. in terms of the ability to mock dependencies in a trivial fashion), to eliminate a lot of Java boilerplate code and thus write less code, and of course to make developing more fun. It's not that I hate Java so much as I feel Java simply isn't innovating anymore and hasn't for a while, and isn't adding features that I simply don't want to live without anymore such as closures and the ability to do metaprogramming when I need to. In addition, it isn't removing features that I don't want, such as checked exceptions. If I know, for a fact, that I can handle an exception, I'll handle it appropriately. Otherwise, when there's nothing I can do anyway, I want to let the damn thing propagate up and just show a generic error message to the user, log the error, and send the admin team an email with the problem details.

This being, for better or worse, a Maven project, we've had some interesting issues with mixed compilation of Java and Groovy code. The GMaven plugin is easy to install and works well but currently has some outstanding issues related to Groovy stub generation, specifically it cannot handle generics or enums properly right now. (Maybe someone will be less lazy than me and help them fix it instead of complaining about it.) Since many of our classes use generics, e.g. in service classes that return domain objects, we currently are not generating stubs. We'll convert existing classes and any other necessary dependencies to Groovy as we make updates to Java classes, and we are implementing new code in Groovy. Especially in the web controller code, this becomes trivial since the controllers generally depend on other Java and/or Groovy code, but no other classes depend on the controllers. So starting in the web tier seems to be a good choice. Groovy combined with implementing controllers using the Spring @MVC annotation-based controller configuration style (i.e. no XML configuration), is making the controllers really thin, lightweight, and easy to read, implement, and test.

I estimate it will take a while to fully convert all the existing Java code to Groovy code. The point here is that we are doing it piecemeal rather than trying to do it all at once. Also, whenever we convert a Java file to a Groovy one, there are a few basics to make the classes Groovier without going totally overboard and spending loads of time. First, once you've used IntelliJ's move refactoring to move the .java file to the Groovy source tree (since we have src/main/java and src/main/groovy) you can then use IntelliJ's handy-dandy "Rename to Groovy" refactoring. In IntelliJ 8.1 you need to use the "Search - Find Action" menu option or keystroke and type "Rename to..." and select "Rename to Groovy" since they goofed in version 8 and that option was left off a menu somehow. Once that's done you can do a few simple things to make the class a bit more groovy. First, get rid of all the semi-colons. Next, replace getter/setter code with direct property access. Third, replace for loops with "each"-style internal iterators when you don't need the loop index and "eachWithIndex" where you do. You can also get rid of some of the redundant modifiers like "public class" since that is the Groovy default. That's not too much at once, doesn't take long, and makes your code Groovier. Over time you can do more groovification if you like.

The most common gotchas I've found have to do with code that uses anonymous or inner classes since Groovy doesn't support those Java language features. In that case you can either make a non-public named class (and it's OK to put it in the same Groovy file unlike Java as long as it's not public) or you can refactor the code some other way (using your creativity and expertise since we are not monkeys, right?). This can sometimes be a pain, especially if you are using a lot of them. So it goes. (And yes, that is a Slaughterhouse Five reference.)

Happy groovification!

Aside from the fact that Oracle's Java Problem contains all kinds of factual and other errors (see the comments on the post) this sentence caught my eye in particular when referring to Java being "quite hard to work with" - "Then, as now, you needed to be a highly trained programmer to make heads or tails of the language."

What's the issue here? That Java is hard to work with? Perhaps more specifically, not just Java but perhaps the artificial complexity in developing "Enterprise" applications in Java? Nope. The problem is that this type of thinking epitomizes the attitude that business people and other "professionals" tend to have about software development in general, in that they believe it is or should be easy and that it is always the tools and rogue programmers that are the problem. Thus, with more and better tools, they reason, there won't be a need for skilled developers and the monkey-work of actually programming could be done by, well, monkeys.

I believe software development is one of the hardest activities humans currently do, and yes I suppose I do have some bias since I am a developer. Also contrary to what many people think, there is both art and engineering involved, and any given problem can be solved in an almost infinite variety of ways. Unlike more established disciplines that have literally been around for hundreds or thousands of years (law, medicine, accounting, architecture, certain branches of engineering like civil, etc.), the software industry hasn't even reached the century mark yet! As a result there isn't any kind of consensus whatsoever about a completely standardized "body of knowledge" and thus there isn't an industy-recognized set of standard exams and boards like you find in the medical and law professions for example. (That topic is for a future post.)

One thing that is certain is that software development involves logic, and thus people who can solve problems using logic will always be needed, whether the primary medium stays in textual format (source code) or whether it evolves into some different representation like Intentional Software is trying to do. So the statement from the article that "you needed to be a highly trained programmer to make heads or tails of the language" is always going to be true in software development. More generally, highly skilled people are needed in any complex endeavor, and attempts to dumb dumb complex things will likely not succeed in any area, not just software development. Would you trust someone to perform surgery on you so long as they have a "Dummies Guide to Surgery" book? Or someone to represent you in court who stayed at a Holiday Inn Express last night?

I hypothesize that things are becoming more complex as time moves on, not less. I also propose that unless we actually succeed in building Cylons who end up wiping us all out or enslaving us, we will never reach a point where we don't need people to actually think and use logic to solve problems. So even though many business-types would love to be able to hire a bunch of monkeys and pay them $0.01 per day to develop software, those who actually realize that highly skilled people are an asset and help their bottom line, and treat them as such, are the ones who will come out on top, because they will smash their competitors who think of software/IT purely as a cost center and not a profit center.

If you want/need to run VisualVM on a 32-bit Macbook Pro you'll need to do a couple of things. First, download and install Soy Latte, using these instructions - this gets you a Java 6 JDK/JRE on your 32-bit Macbook Pro. Second, download VisualVM and extract it wherever, e.g. /usr/local/visualvm. If you now try to run VisualVM you'll get the following error message:

$ ./visualvm
./..//platform9/lib/nbexec: line 489: /System/Library/Frameworks/JavaVM.framework/
Versions/1.6/Home/bin/java: Bad CPU type in executable

Oops. After looking at the bin/visualvm script I noticed it is looking for an environment variable named "jdkhome." So the third step is to export an environment variable named 'jdkhome' that points to wherever you installed Soy Latte:

export jdkhome=/usr/local/soylatte16-i386-1.0.3

Now run the bin/visualvm script from the command line. Oh, almost forgot to mention that you should also have X11 installed, which it will be by default on Mac OS X Leopard. Now if all went well, you should have VisualVM up and running!

Today I was mucking around with the Spring 3.0.0.M1 source release I downloaded as a ZIP file. I wanted to simply get the sample PetClinic up and running and be able to load Spring as a project in IntelliJ. Note Spring now requires Java 6 to build, so if you're using an older 32-bit Macbook Pro you'll need to install JDK 6. I used these instructions generously provided by Landon Fuller to install Soy Latte, which is a Java 6 port for Mac OS X (Tiger and Leopard). So I went to run the "ant jar package" command (after first setting up Ivy since that is how Spring now manages dependencies) and everything went well until I got a compilation exception. There unfortunately wasn't any nice error message about why the compile failed.

So next I loaded up the Spring project in IntelliJ and tried to compile from there. Aha! It tells me that the org.springframework.aop.target package is missing as well as the org.springframework.aop.framework.autoproxy.target package, and of course all the classes in those packages were also missing. I was fairly sure I didn't accidentally delete those two packages in the source code, so I checked the spring-framework-3.0.0.M1.zip file to be sure. Sure enough those two 'target' packages are not present in the source code in the zip file. The resolution is to go grab the missing files from the Spring 3.0.0.M1 subversion repository and put them in the correct place in the source tree. The better resolution is to do an export of the 3.0.0.M1 tag from the Subversion repo directly, rather than be lazy like I was and download the zip file.

I still am wondering why the 'target' packages were missing, however. My guess is that whatever build process builds the zip file for distribution excluded directories named 'target' since 'target' is a common output directory name in build systems like Ant and Maven and usually should be excluded since it contains generated artifacts. If that assumption is correct and all directories named 'target' were excluded, then unfortunately the two aop subpackages named 'target' got mistakenly excluded which caused a bit of head-scratching as to why Spring wouldn't compile.

If you're into Groovy and Spring, check out my two-part series on IBM developerWorks on using Groovy together with Spring's dynamic language support for potentially more flexible (and interesting) applications. In Part 1 I show how to easily integrate Groovy scripts (i.e. .groovy files containing one or more classes) into Spring-based applications. In Part 2 I show how to use the "refreshable beans" feature in Spring to automatically and transparently reload Spring beans implemented in Groovy from pretty much anywhere including a relational database, and why you might actually are to do something like that!

So, after having actually written a blog entry covering each day of the iPhone bootcamp at Big Nerd Ranch, I thought a more broad summary would be in order. (That, and I'm sitting in the airport waiting for my flight this evening.) Anyway, the iPhone bootcamp was my second BNR class (I took the Cocoa bootcamp last April and wrote a summary blog about it here.)

As with the Cocoa bootcamp, I had a great time and learned a ton about iPhone development. I met a lot of really cool and interesting people with a wide range of backgrounds and experiences. This seems to be a trend at BNR, that the people who attend are people who have a variety of knowledge and experience, and bring totally different perspectives to the class. The students who attend are also highly motivated people in general, which, when combined with excellent instruction and great lab coding exercises all week, makes for a great learning environment.

Another interesting thing that happens at BNR is that in this environment, you somehow don't burn out and can basically write code all day every day and many people keep at it into the night hours. I think this is due to the way the BNR classes combine short, targeted lecture with lots and lots and lots of hands-on coding. In addition, taking an afternoon hike through untouched nature really helps to refresh you and keep energy levels up. (Maybe if more companies, and the USA for that matter, encouraged this kind of thing people would actually be more productive rather than less.) And because of the diversity of the students, every meal combines good food with interesting conversation.

So, thanks to our instructors Joe and Brian for a great week of learning and to all the students for making it a great experience. Can't wait to take the OpenGL bootcamp sometime in the future.

Today is Day 5 — the final day — of the iPhone bootcamp at Big Nerd Ranch, taught by Joe Conway. The last day of Big Nerd Ranch bootcamps are half-days so you have breakfast, have class until lunch, have lunch, and then shuttle back to the airport. Unfortunately for me my flight isn't until 7pm so I have a lot of time to write this entry!

See here for a list of each day's blog entries.

Preferences

First up on this last day of iPhone bootcamp is preferences, which allow an app to keep user settings in a centralized location. While you can store user settings yourself using a custom UI, the easiest way is to use the iPhone's built-in Settings app. The Settings app is the central location where apps can store user settings. It is also where all the other common iPhone settings are, which is convenient.

You work with the NSUserDefaults object to store app settings based on the app's bundle ID, for example com.acme.MyKillerApp. You'll also want to ensure you provide "factory default" settings using the registerDefaults method; these settings will be used if the user has not changed anything. NSUserDefaults is basically a dictionary of key-value pairs, and you obtain the standard user defaults using the standardUserDefaults method. From that point you can write user settings using methods like setObject:forKey, setInteger:forKey, and so on, and you can remove settings using removeObjectForKey. Similarly, you read settings using methods like objectForKey, integerForKey, and so forth.

As mentioned earlier, the Settings app is a uniform way of setting preferences for all apps. Users know where to look for setting preferences for apps there. In addition, managing the settings separately from your application also saves screen real estate, which is important since the screen isn't all that big. You define the settings for your application using the Settings Bundle. This is a standard Property List. You use special property keys, such as PSToggleSwitchSpecifier, to define the settings for your application. The Settings app uses the Settings bundle and property list to create the settings UI for your app. For example, if you define settings for a PSToggleSwitchSpecifier, a PSTextFieldSpecifier, and a PSMultiValueSpecifier, the user will see a toggle switch, a text field, and a slider when she goes to edit your app's settings.

For the lab exercise, we modified our Random Number app (from Day 4 during the Web Services section) to have user settings for how the random numbers are generated — for example minimum number and the range of numbers. It is quite easy to add user settings to your app in the iPhone using the Settings app and bundle.

Instruments

Joe briefly talked about using the Instruments app to do powerful debugging, for example to detect memory leaks in your app. He then demonstrated using the Leaks tool within Instruments to track a memory leak — which he had previously introduced intentionally — in the Tile Game app. Leaks was able to pinpoint the exact line of code where a leaked object (i.e. it was not released) was allocated. This is pretty cool.

Joe also showed what leaks look like when they come from C code versus Objective-C code. C-code allocation leaks (i.e. allocated using malloc) show up in Instruments as just 'General Block' and from what I gather are probably not that fun to track down the exact cause. Leaks in Objective-C code are easier, and as I just mentioned, Leaks can show you the exact line of code where a leaked object was allocated.

Networking

By this time, it is getting closer to lunch, and the end of the class. Sad, I know. Anyway, probably one of the hardest and broadest topics was saved for last, given that you could spend an entire course on nothing but network programming. Anyway, on the iPhone a key concept when doing network programming is "reachability." Reachability does not mean that a network resource is definitely available; rather it means the resource is "not impossible" to reach. Another important thing on the iPhone is figuring out what type of connection you have, for example EDGE or 3G or Wi-Fi. You might choose to do different things based on the type of connection.

With the SystemConfiguration framework you can determine if the outside world is reachable, again with the caveat the "reachable" means "not impossible to reach." When coding you work with "reachability references" and "reachability flags" which describe the type of connection, for example reachable, connection required, is wide-area network, and so on.

We then learned a bit about Bonjour, which is basically a zero-configuration network service discovery mechanism that works on all platforms, has implementations in many languages, and is easy to use. For example, Bonjour makes it ridiculously easy to find printers on a network, as opposed to the way you have to do it in other operating systems. You can use Bonjour on the iPhone to discover and resolve Bonjour services. You use NSNetServices and NSNetServiceBrowser to accomplish this, and you specify a delegate to receive notifications when services appear and disappear.

In addition to Bonjour, you can also send and receive data over the network as you would expect. To send and receive data you can either use a C-based Core Foundation interface or use a stream-based interface with CFStream. You register read and write callbacks with the main iPhone run loop, which calls your functions when network events occur.

Network programming is really hard, since there are so many things that can go wrong and you need to deal with many if not all of them. Joe recommended that before jumping right into hardcore networking, developers should become familiar with the concepts and recommended the Beej's guide to network programming as a good primer. Given that I've really only done simple socket programming in higher-level APIs like Java's, and have not really done much of it, I'll need to check that out. And so this concludes this episode of iPhone bootcamp blog, since it is now time for lunch and, sadly, the course is over!

Random Thoughts

This week has been a really intensive introduction to iPhone programming. We've gone from a very simple app on Day 1 and covered all kinds of things like form-based UIs and text manipulation; Core Location; Core Graphics; view transitions and Core Animation; using the iPhone camera and accelerometer; retrieving web-based data; manipulating Address Book data; setting user preferences, and finally networking and debugging using Instruments. We've basically covered an entire book's worth of content and written about 10 iPhone applications ranging from simple to not-so-simple. If you are interested in programming the iPhone, I definitely recommend checking out the iPhone bootcamp at Big Nerd Ranch. Because the OpenGL stuff we did on the iPhone was so cool, I'm thinking my next course to take might be the OpenGL bootcamp but that probably won't happen until next year sometime! With my new knowledge I plan to go home and try my hand at creating a snowflake or snowstorm application that my daughters can play with. If I actually get it working maybe I'll write something about it.

Today is Day 4 of the iPhone bootcamp at Big Nerd Ranch, taught by Joe Conway. Unfortunately that means we are closer to the end than to the beginning.

See here for a list of each day's blog entries.

View Transitions

Since we had not completely finished up the Core Graphics lab from Day 3, we spent the first hour completing the lab exercise, which was to build a "Tile Game" application where you take an image, split it into tiles, and the user can move the tiles around and try to arrange them in the correct way to produce the full image. Actually you don't really split the image; you use a grid of custom objects — which are a subclass ofUIControl — and translate the portion of the image being split to the location in the grid where the tile is located. When a user moves the tiles around, each tile still displays its original portion of the image. So, you are using the same image but only displaying a portion of the image in each tile.

After completing the lab, Joe went over view transitions. View transitions allow you to easily add common animations (like the peel and flip animations you see on many iPhone apps) to your applications to create nice visual effects and a good user experience. For example, in our Tile Game app, when you move a tile it abruptly jumps from the old location to the new location with no transition of any kind. Also, when you touch the "info" button to select a new tiled-image there is no animation. It would be better to make the tiles slide from square to square, and to flip the tile over to the image selection screen. View transitions let you do this pretty easily. (Joe mentioned that later we'll be covering Core Animation which is more powerful and lets you perform all kinds of advanced animations.)

So, to reiterate, view transitions are meant for simple transitions like flipping, peeling, and so on. There are several "inherently animatable" properties of a UIView: the view frame, the view bounds, the center of the view, the transform (orientation) of the view, and the alpha (opacity) of the view. For example, to create a pulsing effect you could peform two alpha animations one after the other: the first one would transition the view from completely opaque to completely transparent, and the second animation would transition back from completely transparent to completely opaque. For the View Transition lab we used a "flip" animation to flip between views.

You use class methods of UIView to begin animations, setup view transitions, and commit the transitions. You use beginAnimations to begin animations. Then you define the animations using methods like setAnimationDuration and setAnimationTransition, which set the length of time over which the animation occurs and the type of animation such as peel or flip, respectively. Then you perform actions like add and remove subviews or perform transitions on any of the "inherently animatable" properties in an "animation block." To start the animations on screen you call commitAnimations after the animation block. This seems similar to how transactions work in a relational database, in that you begin a transaction, define what you want done, and then when satisfied you commit those "changes." Joe mentioned that Core Graphics essentially uses a hidden or offscreen view to store the actions and only shows the animations and actions when the animations are committed.

Core Animation

Next up: Core Animation. While view transitions are for simple animations, with Core Animation you can animate almost anything you want. The basic idea here is that when using Core Animation, the animation takes place on a CALayer rather than the UIView. There is one CALayer per UIView, and the CALayer is a cached copy of the content in the UIView. As soon as an animation begins, the UIView and CALayer are interchanged, and all drawing operations during the animation take place on the CALayer; in other words when an animation begins the CALayer becomes visible and handles drawing operations. After the animation ends the UIView is made visible again and the CALayer is no longer visible, at which point the UIView resumes responsibility for drawing.

You create animations using subclasses of CAAnimation and adding them to the CALayer. CABasicAnimation is the most basic form of animation: you can animate a specific property, known as a key path, to perform a linear transition from an original value to a final value. For example, using a key path of "opacity" you can transition an object from opaque to translucent, or vice versa.

You can also combine multiple animations using a CAAnimationGroup, which is itself a subclass of CAAnimation (hey, that's the Composite design pattern for anyone who cares anymore). You can use CAKeyframeAnimation to perform nonlinear animations, in which you have one or more "waypoints" during the animation. In other words, with CAKeyframeAnimation you define transitions for a specific attribute — such as opacity, position, and size — that have different values at the various waypoints. For example, in the Core Animation lab exercise we defined a rotation animation to "jiggle" an element in the Tile Game we created earlier to indicate that a tile cannot be moved. The "jiggle" animation uses the CAKeyframeAnimation to rotate a tile left, then right, then left, then right, and finally back to its original position to give the effect of it jiggling back and forth several times.

To finish up Core Animation, Joe covered how to use Media Timing Functions to create various effects during animations. For example, we used CAMediaTimingFunctionEaseIn while sliding tiles in the Tile Game. Ease-in causes the tile animation to start slowly and speed up as it approaches the final location. Finally, I should mention that, as with most iPhone APIs, you can set up a delegate to respond when an animation ends using animationDidStop. For example, when one animation stops you could start another one and chain several animations together.

Camera

After a cheeseburger and fries lunch, we learned how to use the iPhone's camera. The bad news about the camera is that you can't do much with it: you can take pictures (obviously) and you can choose photos from the photo library. The good news is that using the camera in code is really simple. You use a UIImagePickerController, which is a subclass of UINavigationController, and push it modally onto the top view controller using the presentModalViewController:animated method. Since it is modal, it takes over the application until the user cancels or finishes the operation. Once a user takes a picture or selects one from the photo library, UIImagePickerController returns the resulting image to its delegate.

There are two delegate methods you can implement. One is called when the user finishes picking an image and the other is called if the user cancelled the operation. The delegate method called when a user selects a picture returns the chosen image and some "editingInfo" which allows you to move and scale the image among other things. The lab exercise for the camera involved modifying the Tile Game to allow the user to take a photo which then becomes the game's tiled-image.

Accelerometer

The accelerometer on the iPhone is cool. It measures the G-forces on the iPhone. You use a simple, delegate-based API to handle accelerations. While the API itself is pretty simple, the math involved and thinking about the orientation of the iPhone and figuring out how to get the information you want is the hard part. But you'd kind of expect that transforming acceleration information in 3D space into information your application can use isn't exactly the easiest thing. (Or, maybe it's just that I've been doing web applications too long and don't know how to do math anymore.)

There is one shared instance of the accelerometer, the UIAccelerometer object. As you might have guessed, you use a delegate to respond to acceleration events, specifically the accelerometer:didAccelerate method which provides you the UIAccelerometer and a UIAcceleration object. You need to specify an update interval for the accelerometer, which determines how often the accelerometer:didAccelerate delegate method gets called.

The UIAcceleration object contains the measured G-force along the x, y, and z axes and a time stamp when the measurements were taken. One thing Joe mentioned is that you should not assume a base orientation of the iPhone whenever you receive acceleration events. For example, when your application starts you have no idea what the iPhone's orientation is. To do something like determine if the iPhone is being shaken along the z-axis (which is perpendicular to the screen) you can take an average of the acceleration values over a sample period and look at the standard deviation; if the value exceeds some threshold your application can decide the iPhone is being shaken and you can respond accordingly. For the lab exercise, we modified the Tile Game to use the accelerometer to slide the tiles around as the user tilts the iPhone and to randomize the tiles if the user shakes the iPhone. Pretty cool stuff!

Web Services

Well, I guess the fun had to end at some point. That point was when we covered Web Services, mainly because it reminded me that, no, I'm not going to be programming the iPhone next week for the project I'm on, and instead I'm going to be doing "enterprisey" and "business" stuff. Oh well, if we must, then we must.

Fortunately, Joe is defining web services as "XML over HTTP" and not as WS-Death-*, though of course if you really want to reduce the fun-factor go ahead Darth. To retrieve web resources you can use NSURL to create a URL, NSMutableURLRequest to create a new request, and finally NSURLConnection to make the connection, send the request, and get the response. You could also use NSURLConnection with a delegate to do asynchronous requests, which might be better to prevent your application's UI from locking up until the request completes or times out.

If you have to deal with an XML response, you can use NSXMLParser, which is an event-based (SAX) parser. (By default there is no tree-based (DOM) parser on the iPhone, but apparently you can use libxml to parse XML documents and get back a doubly-linked list which you can use to traverse the nodes of the document.) You give NSXMLParser a delegate which recieves callbacks during the parse, for example parserDidStartDocument and parser:didStartElement:namespaceURI:qualifiedName:attributes. Then it's time to kick it old school, handling the SAX events as they come in, maintaining the stack of elements you've seen, and writing logic to respond to each type of element you care about. For our Web Services lab we wrote a simple application that connected to random.org, which generates random numbers based on atmospheric noise, and made a request for 10 random numbers, received the response as XHTML, extracted the numbers, and finally displayed them to the user.

Address Book

Last up for today was using the iPhone Address Book. There are two ways to use the address book. The first way leverages the standard iPhone Address Book UI. The second uses a lower-level C API in the AddressBook framework.

When you use the Address Book UI, you use the standard iPhone address book interface in your application. It allows the user to select a person or individual items like an email address or phone number. You must have a UIViewController and define a delegate conforming to ABPeoplePickerNavigationControllerDelegate protocol. You then present a modal view controller passing it a ABPeoplePickerNavigationController which then takes over and displays the standard iPhone address book application. You receive callbacks via delegate methods such as peoplePickerNavigationController:shouldContinueAfterSelectingPerson to determine what action(s) to take once a person has been chosen. You, as the caller, are responsible for removing the people picker by calling the dismissModalViewControllerAnimated method. We created a simple app that uses the Address Book UI during the first part of the lab exercise.

Next we covered the AddressBook framework, which is bare-bones, pedal-to-the-metal, C code and a low-level C API. However, you get "toll-free bridging" of certain objects meaning you can treat them as Objective-C objects, for example certain objects can be cast directly to an Objective-C NSString. Another thing to remember is that with the AddresBook framework there is no autorelease pool and you must call CFRelease on objects returned by methods that create or copy values. Why would you ever want to use the AddressBook framework over the Address Book UI? Mainly because it provides more functionality and allows you to directly access and potentially manipulate, via the API, iPhone address book data. For the second part of the Address Book lab, we used the AddressBook API to retrieve specific information, such as the mobile phone number, on selected contacts.

Random Thoughts

Using View Transitions and Core Animation can really spice up your apps and create really a cool user experience. (Of course you could probably also create really bad UIs as well if overused.) The camera is pretty cool, but the most fun today was using the accelerometer to respond to shaking and moving the iPhone. Web services. (Ok, that's enough on the enterprise front.) Last, using the various address book frameworks can certainly be useful in some types of applications where you need to select contacts.

Something in one of the labs we did today was pretty handy, namely that messages to nil objects are ignored in Objective-C. There are a lot of times this feature would be hugely useful, though I can also see how it might cause debugging certain problems to be really difficult! There's even a design pattern named the Null Object Pattern since in languages like Java you get nasty things like null-pointer exceptions if you try to invoke methods on a null object.

Man, we really covered a lot today, and now I am sad that tomorrow is the last day of iPhone bootcamp. I should become a professional Big Nerd Ranch attendee; I think that would be a great job!