Archive for iphone sdk

Working with Orientation Changes on the iPhone Part 2

// June 14th, 2009 // No Comments » // iphone, iphone sdk, objective-c, orientation changes, xcode

In my last post I outlined a scheme for working with orientation changes on the iPhone. Sadly, that scheme does not work on iPhone OS3.0 so I rewrote the code to work for OS3.0. You can download the XCode project here: XCode Project

This is a slightly simpler approach and doesn’t rely on any of the SDK code for reorienting things. In some ways you have more control over what you are doing but you have to code the animations by hand. Let me know in the comments if it works for you.

Working with Orientation Changes on the iPhone

// May 1st, 2009 // 6 Comments » // auto-rotation, code, iphone, iphone sdk, orientation changes, programming, sample code, viewcontroller

Update: It looks like Apple has change the way shouldAutoRotateToInterfaceOrientation works in iPhone SDK 3.0. Here is my updated post on how to do this differently.

One of the features with which I had to get fairly intimate with on the iPhone over the last couple of months was working with orientation changes. At first my code was completely incorrect and it wasn’t immediately obvious to me how to get my application to reorient itself properly. This was mainly due to the structure of my code. In this post I am going to explain a simple, memory efficient way of working with UIViewController and interface orientation changes.

1. The Basics

Before we get into the nitty gritty let’s first have a recap of how interface orientation changes work and how you should respond to them. Firstly, if you want your view to auto-rotate you need to override the method shouldAutorotateToInterfaceOrientation: and return YES. If you want to only allow auto-rotation under a certain condition you can put the test for this condition in this method too.

This is pretty much the most basic thing you need to do to allow for auto-rotation but there are additional methods you can override that can be very useful. These methods are

• willRotateToInterfaceOrientation

• didRotateFromInterfaceOrientation

• willAnimateFirstHalfOfRotationToInterfaceOrientation

• willAnimateSecondHalfOfRotationFromInterfaceOrientation

The first 2 methods are very useful for doing pre- and post-processing of your rotation. You could perhaps initialize a view controller or add some views to your current view in the willRotateToInterfaceOrientation. The second 2 are pretty much self explanatory. If you want to perform additional operations during that particular phase of the rotation you can implement them too.

Another very useful code example for when working with view controller orientations is:

    //do some processing…
}else if(UIInterfaceOrientationIsPortrait(interfaceOrientation)){
    //do different processing…}
else if(UIDeviceOrientationIsValidInterfaceOrientation(interfaceOrientation)){
    //do something

Most programmers aren’t aware of these macros and they do cut down and simplify code.

2. Loading & Unloading View Controllers

To save on memory usage you can load and unload view controllers as your interface orientation changes. I found this incredibly useful as my application required a fair amount of memory. It basically works on the principle that the application’s delegate class will manage the changing of the view controllers.

In you application delegate you can add the following method:

- (void) switchViewControllers:(UIViewController *)controller{
if(self.viewController != nil){
    [viewController.view removeFromSuperview];
    self.viewController = controller;
    [window addSubview:self.viewController.view];

Make sure you have a viewController property on the application delegate of course.

When switchViewControllers is called, your currently visible view is removed from its superview and the new view controller and its associated view are added.

The next step is to add this piece of code inside your view controllers that you want to switch out during auto rotation:

- (BOOL)shouldAutorotateToInterfaceOrientation:
                (UIInterfaceOrientation)interfaceOrientation {
    CustomUIViewController *customUIViewController = 
                [[CustomUIViewController alloc] init];
    MyAppDelegate *appDelegate = 
        (MyAppDelegate *)[[UIApplication sharedApplication] delegate];
    appDelegate switchViewControllers: customUIViewController];
    [customUIViewController release];

Where CustomUIViewController is your own view controller you want to switch to.

3. Pitfalls

This approach has worked very well for me but I did have an issue where I was using 3 view controllers. Let’s call them A, B and C. A switched to B and vice-versa when the phone’s orientation changed. C was loaded by B and was viewable in landscape and portrait orientations. The problem came in where if you changed C’s orientation and then the user navigated back to B where B had a different orientation, you would effectively not be notified of an orientation change. If you subsequently changed B’s orientation to load A, you would find A would load in the wrong orientation. Oops, bug…

After trolling a number forums I discovered there used to be an undocumented call in the SDK called changeOrientation: but for some or other reason Apple removed this method.

So how did I solve this? Well all I did was put this piece of code in A so that it would manually reorient itself from portrait to landscape:

- (void)viewDidAppear:(BOOL)animated {
        [UIView beginAnimations:@”View Flip” context:nil];
        [UIView setAnimationDuration:0.5f];
        [UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
        self.view.transform = CGAffineTransformIdentity;
        self.view.transform = 
            CGAffineTransformMakeRotation(MPI * (90) / 180.0);
        self.view.bounds = CGRectMake(0.0f, 0.0f, 480.0f, 320.0f); = CGPointMake(160.0f, 240.0f);
        [UIView commitAnimations];

Conversely you can use this piece of code to reorient from landscape to portrait if your “A” view controller needs to be in portrait mode:

- (void)viewDidAppear:(BOOL)animated {
        [UIView beginAnimations:@”View Flip” context:nil];
        [UIView setAnimationDuration:0.5f];
        [UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
        self.view.transform = CGAffineTransformIdentity;
        self.view.transform = 
            CGAffineTransformMakeRotation(MPI * (90) / 180.0);
        self.view.bounds = CGRectMake(0.0f, 0.0f, 320.0f, 480.0f);
        [UIView commitAnimations];

So far this method of loading and unloading view controllers on orientation changes has proved to be very memory efficient and not too performance intensive either. Let me know in the comments if it works for you or if you have any ideas about this method of managing view controllers and orientation changes.

Programming Lessons: iPhone Style

// April 10th, 2009 // No Comments » // 42 restaurants, application, iphone, iphone sdk, objective-c, programming, xcode

I have been really busy, as many of you have noticed, the last few months juggling my job at ChessCube and building an iPhone application. I have even gone so far as to only work for ChessCube part-time in order to make time to build my application.

The application I have busy building is called 42 Restaurants and it was a concept my girlfriend, Margarét, and I came up with one day while sitting in a sushi restaurant. It goes along the lines of producing a really beautiful iPhone application that showcases recipes from some of the best restaurants in the world. You can read more on the 42 Restaurants website here.

The concept started out simple. My knowledge at the time of the iPhone SDK was very basic and we didn’t want to be too ambitious. The main features would be amazing pictures, simple functionality and great recipes; all the while providing good marketing for the restaurants involved.

Now that we are nearing the end of developing the application, I can let everyone in on some tips to hopefully help their progress with their own application.

1. Read, Read, Read

The main thing that stood me in good stead for learning the SDK was reading. I read everything, from the Apple developer documentation to blogs and online tutorials. The two books that really helped me the most were - The iPhone Developers Cookbook By Erica Sadun and Cocoa Programming for Mac OS X by Aaron Hillegass. The best thing about these two books is that the former teaches you how to build and use components in the SDK without needing to worry about things like code structure and development tools. The latter teaches you the fundamentals of Cocoa programming – even though it contains no coverage of the iPhone SDK.

Understanding the basics is key to using the iPhone SDK.

2. Get To Know XCode

Coming from a development environment from Eclipse, XCode seems at first very different and at times a bit clunky. Now that I have figured out how to use a large portion of it, I can honestly say that I love it. Its simple, fast and it isn’t intrusive while you are coding. One tip which I think most Eclipse & Netbeans programmers will appreciate is to change the Layout Mode. Go to XCode->Preferences->General and change the Layout to All-In-One. All your XCode windows will then be grouped into one place and the interface will alter itself depending on whether your are debugging or coding.

Another important thing to do is download all the SDK documentation to XCode. Take a look at this great blog post to see how to do it without having to use XCode’s built-in documentation downloading mechanisms.

3. Understand How Interface Builder Works

From reading numerous forums on the topic, programmers seem to find it difficult to understand Interface Builder (IB). I was one of them. My distrust of WYSIWYG interface tools led me to building all my view code manually. This, as you can imagine, took me forever until I spent some time trying to understand IB. Now, I pretty much build all my components in IB.

The main concept I had difficulty grasping with IB was what piece of code fitted with what. Each XIB file has two parts, a File’s Owner and a View. The File’s Owner is a class that inherits from UIViewController and the View can be any class that inherits from UIView.

If you want to initialize a XIB file all you need to do is instantiate your view controller with the method initWithNibNamed and then add the view of that view controller as a subview of whatever view you are currently displaying. If you want to do any post instantiation initialization, such as setting text for a UILabel or applying an image to a UIImageView then you override the method viewDidLoad in your view controller.

Don’t forget of course to wire up your IBOutlets and your IBActions in your File’s Owner to your View and to set your File’s Owner to be the custom view controller that you have created in XCode. Otherwise, your view will load and nothing will happen.

4. Don’t Do Cut-and-Paste Coding

This seems to be the number one problem in the development community. There are too many programmers that try to code by searching the Internet looking for solutions to their particular problem. Cutting some sample code from a blog or forum post. Pasting it into their project only to find A) it doesn’t work, B) it is full of bugs or C) badly written.

Understand the principles of what you are trying to do before you go on the web to find a solution. Often you will save time writing the component/algorithm from the ground up and even if you don’t, you will have learnt a lot in the process. The next time you have to build something similar you can use that knowledge.

5. Don’t Be Scared to Rewrite Code

My application was about 80% complete when I realized I was coding around my solution. The architecture that I had designed was firstly, very inefficient memory-wise and secondly, limiting me in terms of the functionality I needed to add. When I started the project I had a very basic understanding of Objective-C and the iPhone SDK, and my solution thus far had evolved into a big, code beast. So I spent 2 days rewriting the core of the application. I lost 2 days but I gained a whole bunch of functionality, improved memory usage and reduced my code base considerably.

6. Lessons

42 Restaurants will hopefully get into the App Store at the end of April. Although the idea seemed simple to start off with, it has grown into a fully fledged recipe application. The sheer amount of design work that Margarét has put into it, makes it in my mind, a masterpiece. Each individual recipe has been custom designed and the application is looking amazing because of it. We both wanted to the application first and foremost to blow the user away with how great it looks and I think we are there.

I hope the code-work on my part will live up to the task. Keep watching this blog and the 42 Restaurants website for news on the launch. We are also on the threshold of starting a round of user testing, so if you have an iPhone and would like to check what we have built so far, post a comment and I will add you to my list of testers.

iPhone Developer Program Accepted

// October 19th, 2008 // 5 Comments » // emulator, iphone, iphone developer program, iphone sdk, programming, simulator

Woohoo! I just got accepted into the iPhone Developer Program after applying 3 weeks ago. In that time the price of the membership jumped R250 due to currency fluctuations, which can be viewed as a good or a bad thing depending on when I can get my application released into the store. If I can get it done before the rand strengthens against the dollar I will make the money back fairly quickly.

In any case, I can now test my iPhone application on a real-world iPhone rather than using the iPhone SDK simulator. This has a few advantages. Firstly, the simulator is exactly what it says it is; it is just a simulator not to be confused with an emulator. Therefore, all the apps that I test on it have access to my MacBook Pro’s 4gigs of memory and powerful CPU which is much larger than what I have available on the iPhone. This is not the best testing environment as not having the ability to test my applications on a real-world device would mean I would have no clue how fast the application would run.

Another limitation of the simulator is that I am unable to test additional hardware elements of the phone, such as the accelerometer, the GPS and the multi-touch interface. (Note: You can test multi-touch on the simulator by holding the Option-key while dragging your mouse around but its not very easy to use.)

I will be releasing a tutorial shortly on how to get your applications to run on your iPhone using the provisioning certificates that Apple provides once you have been accepted into the iPhone Developer Program.

Objective-C: Tips for a Java Programmer

// October 12th, 2008 // 7 Comments » // instruments, iphone, iphone sdk, java, java objective-c comparison, key-value coding, learning, objective-c, programming, xcode

I have been learning Objective-C part-time. Partly to learn something new and different but also partly out of curiosity. As a Java programmer, I initially thought it would be a doddle but as soon as I looked at the code I realised it was going to take a bit of getting used to. After going through Apple’s excellent, yet verbose, guide: The Objective-C 2.0 Programming Language – I started to get used to the syntax. Its not that hard, especially if you come from a C or Java background. Here are some of the differences and some of the highlights I have encountered so far.

1. Methods, Functions, Messaging

The most difficult thing to get used to initially is the syntax for calling methods, or as its called in Objective-C: messaging. In Java calling a method on an object looks like this:

Car car = new Car();, 100);

This piece of code creates an instance of type car and then tells it drive 10 kilometres at 100 kilometres and hour. If we were to write the same thing in Objective-C it would look something like this:

Car car = [[Car alloc] init];
[car drive:10 speed:100];

Whoaaa! Hold on a minute. That is completely different from Java and C. Well, don’t panic. If you have ever programmed with C or C++ you will probably understand the first bit – Car *car. We are creating a pointer to a place in memory that holds a car. The part after the equals is a little more confusing. The designers of Objective-C have dropped the dot-notation completely for messaging objects. The piece of code [Car alloc] can be rewritten in Java as Car.alloc(). In Objective-C, this is the way to allocate a piece of memory for your instance. It is also the way you call methods on instances.

The closest equivalent to a constructor that I can find in Objective-C is the init message call. All objects have an init method – inherited from the base object NSObject (in Java this would be equivalent to Object). You can override the init method in your classes to add initialisation code.

So the first line in our example now makes sense, but what about the second line? Objective-C uses the concept of named arguments. This may seem redundant or a little verbose, but once you get used to it, it does make it easier to read. This syntax scheme is an adaptation of the way you would message objects in Smalltalk. So we are basically messaging our instance of car to drive 10 at the speed of 100. I could have possibly made the method a little more informative and written it as: [car driveFor:10 speed:100].

2. Garbage Collection vs. Retain Counts

Since Mac OS X 10.5, Mac developers have been treated to the simplicity of writing code without having to worry about memory management – in other words, Garbage Collection has been introduced. The only thing to bear in mind is that if you want to write code that is supported by older versions of Mac OS X, namely, 10.4 and the iPhone you will still need manage your memory manually. Fortunately, detecting memory leaks is fairly simple with the Apple developer tool Instruments.

The mechanism by which you manage memory manually is called retain counts. Every time you make an object point to another object you increase that object’s retain count. This loosely means that if you have 10 pointers pointing to an instance, the instance will have a retain count of 10. Whenever you are finished with a pointer you need to release the object. This drops the instance’s retain count by 1. When an instance’s retain count reaches 0 it will be deallocated.

There are many pitfalls with manual memory management. Having a memory leak means that over time your application will consume more and more memory and it will crash the system eventually. There are 2 main ways you can create a memory leak. The first is to have an orphaned object. This is where the object has a retain count greater than zero but there are no other objects pointing to it. The other is to have a retain cycle. This is where Object A points to Object B and Object B points to Object A, and nothing else points to these two objects.

If you want to build applications for the iPhone or for older versions of Mac OS X then you need to be more meticulous with your code. Make sure that your objects always clean up after themselves and use the application Instruments to ensure you have no memory leaks. On the iPhone memory leaks can be disastrous, since you only have a very limited amount of memory to play with. Should your application run out of the allocated memory on the iPhone, it will reboot – basically quit your application.

3. Cool Extras

Objective-C has some really cool features built into it and some downright weird ones. Two really cool features that have no equivalents in Java are: Key-Value Coding and @synthesize/@property directives.

Key-Value Coding is a very neat and dynamic way of querying objects by name. Some people would say that you can do similar tricks in Java with Reflection but Key-Value Coding has a lot more useful features that you cannot leverage in Java without writing a lot of code.

Key-Value Coding works like this:

Car *car = [[Car alloc] init];
[car setValue:@”BMW” forKey:@”carMaker”];

Basically, we are setting the value for the property carMaker to BMW. This seems cumbersome, but bear with me. We can now retrieve the value in the following manner:

NSString *carMakerString = [car valueForKey:@”carMaker”];

We can now read and set objects by their values. The cool thing is that you don’t need to cast any values. The valueForKey method will automatically cast the value for you. Programmer’s used to dynamic languages will probably laugh at the significance of this but if you are from a Java background you will appreciate not having to check and cast the result of the call.

You can also describe keypaths for key-values. A keypath is basically a way of navigating a pointer graph to a property from object to object. For example:

NSNumber topSpeed = [car valueForKeyPath:@”carMaker.topSpeed”];

Where topSpeed is a method that returns an int for the car’s top speed. The int will be auto-boxed to an NSNumber at runtime.

In addition to keypaths, there are also aggregator functions you can use on key-values in arrays. So for instance, if we have an array of car objects and we want the average top speed of all the cars at the BMW dealer we could do the following:

double averageSpeed = [bmwDealer valueForKey:@”cars.@avg.topSpeed”];

If we wanted to something similar in Java or without key-values we would have to loop through the whole array of cars, add the top speeds to a variable and then divide by the number of cars in the array. If you want to learn more about Key-Value Coding, including the most powerful feature for binding values, called Key-Value Observing, check this article out.

Another cool feature that Objective-C contains, that I use all the time are the @property/@synthesize preprocessor directives. The combination of these eliminates the need to write boilerplate getter and setter code. The @property directive, used in the header file for a class, tells the compiler that this is a property of the class. In addition you can make the property read only or readable/writable, by adding read or readwrite in brackets like this:

@property(read) int topSpeed;


@property(readwrite) NSString carMaker;

You can also tell the compiler how to manage the memory for the getter and setter of that property by putting a retain, assign or copy after. Like this:

@property(read, retain) NSString carMaker;

By adding @synthesize in your class file for your properties. The compiler will automatically generate getter and setter methods for you.

@synthesize carMaker;

4. So Far, So Good

So far my experiences with Objective-C have been favourable. I do get confused sometimes when my code won’t compile and it looks correct, only to realise that it would be correct in Java but will never work in Objective-C. Apple’s Interface Builder software is top notch and makes designing and hooking up your interface very simple. XCode’s code editore on the other hand, in my opinion, is a bit behind compared to Eclipse. A Mac developer would, however, probably class Eclipse as bloatware. Instruments is my favourite and makes optimising your application and finding memory leaks a doddle.