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  • 1. Our Website : /
  • 2. Introduction to Objective C part 1
  • 3. An overview of Objective C  Learning how to develop software can be one of the most intimidating prospects for any computer enthusiast, and with the growing saturation of applications in mobile marketplaces, it is becoming increasingly difficult to get your work noticed.  That’s what this series is for, helping you learn ios development from a conceptual perspective. No prior knowledge of computer programming will be necessary. Over the coming weeks, we’ll examine the iPhone’s ability to deliver immersive, intuitive content, a unique opportunity for both developers and consumers.
  • 4. A Brief History of Objective-C ◦ Objective-C can be traced back to the early 1980s. ◦ Building upon Smalltalk, one of the first object-oriented language, Cox’s fascination with problems of reusability in software design and programming resulted in the creation of the language. ◦ Recognizing that compatibility with C was crucial to the success of the project, Cox began writing a pre- processor for C to add backward compatibility with C, which soon grew into an object-oriented extension to the C language.
  • 5. Conti  In 1986, Cox published a book about the language entitled Object- Oriented Programming, An Evolutionary Approach.  Although the main focus of the instructional text was to point out the issue of reusability, Objective-C has been compared feature-for- feature with the major players in the programming game every since.  After Steve Jobs’ departure from Apple, he started a new company called NeXT.  In 1988, NeXT licensed Objective-C from the owner of the trademark, releasing its own Objective-C compiler and libraries on which the NeXTstep UI and interface builder were based.  The innovative nature of this graphics-based interface creation resulted in the creation of the first web browser on a NeXTstep system.
  • 6. Cont.. ◦ At the Worldwide Developers Conference in 2006, Apple announced Objective-C 2.0, a revision of Objective-C that included syntax enhancements, performance improvements, and 64-bit support. ◦ Mac OS X officially included a 2.0-enabled compiler in October 2007. ◦ It is unclear at this time whether these language changes will be available in the GNU runtime, or if they will be implemented to be compliant with the larger Objective-C 2.0 standard.
  • 7. Differentiates Objective-C from Other C Languages?  Objective-C is essentially an extremely thin layer on top of C, making it a superset of the language.  Moreover, it is possible to compile any C program with an Objective-C compiler, including C code within an Objective-C class.  All non-object-oriented syntax operations are derived from C, while the object-orientation features an implementation akin to Smalltalk messaging.
  • 8. Cont… ◦ Messages - Object-oriented programming is based on message passing to object instances. Objective-C does not call methods, but rather will send a message. ◦ ◦ The target of the message is resolved at runtime, with the receiving object interpreting the message. ◦ The object to which the message is directed is not guaranteed to respond to a message, and if it does not, it simply raises an exception
  • 9. Interfaces and Implementations  Objective-C requires that the implementation of a class be in separately declared code blocks, which has led developers to the convention to place interface in the .h header file and implementation in suffixed with .m, similar to those found in C.
  • 10. Cont..  The implementation method is found within files designated with the suffix .m, which are written using interface declarations. Internal representations of a method vary between different implementations, but the internal names of the function are rarely used directly. Messages are converted to function calls defined in the Objective-C runtime library.
  • 11. Cont..  Dynamic Typing –  Like Smalltalk, Objective-C can send a message to an object that is not specified in the interface, allowing for increased flexibility.  This behavior is known as message forwarding and sometimes delegation.  An error can be used in case the message cannot be forwarded and messages that are never received can silently drop into the background.  Static typing information can be optionally added to variables, which is checked during compilation.
  • 12. Cont..  Instantiation –  Once a class is written, it can be instantiated, meaning that a copy of an object is captured in an instance, which share the same attributes, but the specific information within these attributes differ.  An example of this would be if you were to create a class called “Employee,” describing all attributes common to employees.  They all have names and salaries, but they differ in the numerous cases that will show up.
  • 13. Introduction to Objective C part 2
  • 14. Objective-C Data Types and Variables  One of the fundamentals of any program involves data, and programming languages such as Objective-C define a set of data types that allow us to work with data in a format we understand when writing a computer program.  For example, if we want to store a number in an Objective-C program we could do so with syntax similar to the following:  Syantax int mynumber = 10;
  • 15. Objective-C Expressions  Now that we have looked at variables and data types we need to look at how we work with this data in an application.  The primary method for working with data is in the form of expressions.  int myresult = 1 + 2;
  • 16. Operator Description x += y Add x to y and place result in x x -= y Subtract y from x and place result in x x *= y Multiply x by y and place result in x x /= y Divide x by y and place result in x x %= y Perform Modulo on x and y and place result in x x &= y Assign to x the result of logical AND operation on x and y x |= y Assign to x the result of logical OR operation on x and y x ^= y Assign to x the result of logical Exclusive OR on x and y Objective-C supports the following compound assignment operators:
  • 17. Objective-C Flow Control with if and else  Such decisions define which code gets executed and, conversely, which code gets by-passed when the program is executing.  his is often referred to as flow control since it controls the flow of program execution.  The if statement is perhaps the most basic of flow control options available to the Objective-C programmer.  The basic syntax of the Objective-C if statement is as follows: if (boolean expression) { // Objective-C code to be performed when expression evaluates to true }
  • 18. Looping with the for Statement  The syntax of an Objective-C for loop is as follows:  for ( ''initializer''; ''conditional expression''; ''loop expression'' )  {  // statements to be executed  }  The initializer typically initializes a counter variable. Traditionally the variable name i is used for this purpose, though any valid variable name will do.
  • 19. Objective-C Looping with do and while ◦ The Objective-C for loop described previously works well when you know in advance how many times a particular task needs to be repeated in a program. ◦ There will, however, be instances where code needs to be repeated until a certain condition is met, with no way of knowing in advance how many repetitions are going to be needed to meet that criteria. ◦ To address this need, Objective-C provides the while loop. ◦ The while loop syntax is defined follows: while (''condition'') { // Objective-C statements go here }
  • 20. Objective-C do ... while loops ◦ It is often helpful to think of the do ... while loop as an inverted while loop. The while loop evaluates an expression before executing the code contained in the body of the loop. ◦ If the expression evaluates to false on the first check then the code is not executed. The do ... while loop, on the other hand, is provided for situations where you know that the code contained in the body of the loop will always need to be executed at least once. ◦ The syntax of the do ... while loop is as follows: do { // Objective-C statements here } while (''conditional expression'')
  • 21. Introduction to Objective C part 3
  • 22. Object  Objects are self-contained modules of functionality that can be easily used, and re-used as the building blocks for a software application.  Objects consist of data variables and functions (called methods) that can be accessed and called on the object to perform tasks.  These are collectively referred to as members.
  • 23. Class  Much as a blueprint or architect's drawing defines what an item or a building will look like once it has been constructed, a class defines what an object will look like when it is created.  It defines, for example, what the methods will do and what the member variables will be.
  • 24. Declaring an Objective-C Class Interface  Before an object can be instantiated we first need to define the class 'blueprint' for the object.  In this chapter we will create a Bank Account class to demonstrate the basic concepts of Objective-C object oriented programming.  An Objective-C class is defined in terms of an interface and an implementation.  In the interface section of the definition we specify the base class from which the new class is derived and also define the members and methods that the class will contain. The syntax for the interface section of a class is as follows: @interface NewClassName: ParentClass { ClassMembers; } ClassMethods; @end
  • 25. Cont..  The ClassMethods section defines the methods that are available to be called on the class.  These are essentially functions specific to the class that perform a particular operation when called upon.  To create an example outline interface section for our BankAccount class, we would use the following @interface BankAccount: NSObject {} @end
  • 26. Adding Instance Variables to a Class  A key goal of object oriented programming is a concept referred to as data encapsulation.  The idea behind data encapsulation is that data should be stored within classes and accessed only through methods defined in that class.  Data encapsulated in a class are referred to as instance variables.  Instances of our BankAccount class will be required to store some data, specifically a bank account number and the balance currently held by the account.  Instance variables are declared in the same way any other variables are declared in Objective-C. We can, therefore, add these variables as follows: @interface BankAccount: NSObject { double accountBalance; long accountNumber; } @end
  • 27. Define Class Methods  The methods of a class are essentially code routines that can be called upon to perform specific tasks within the context of an instance of that class.  Methods come in two different forms, class methods and instance methods.  Class methods operate at the level of the class, such as creating a new instance of a class.  Instance methods, on the other hand, operate only on the instance of a class (for example performing an arithmetic operation on two instance variables and returning the result).  Class methods are preceded by a plus (+) sign in the declaration and instance methods are preceded by a minus (-) sign. -(void) setAccountNumber: (long) y;
  • 28. Declaring an Objective-C Class Implementation  The next step in creating a new class in Objective-C is to write the code for the methods we have already declared.  This is performed in the @implementation section of the class definition.An outline implementation is structured as follows: @implementation NewClassName ClassMethods @end  In order to implement the methods we declared in the @interface section, therefore, we need to write the following code:  @implementation BankAccount -(void) setAccount: (long) y andBalance: (double) x; { accountBalance = x; accountNumber = y; }
  • 29. Declaring and Initializing a Class Instance  so far all we have done is define the blueprint for our class. In order to do anything with this class, we need to create instances of it.  The first step in this process is to declare a variable to store a pointer to the instance when it is created. We do this as follows: BankAccount *account1;  Having created a variable to store a reference to the class instance, we can now allocate memory in preparation for initializing the class: account1 = [BankAccount alloc];
  • 30. Automatic Reference Counting (ARC)  In the first step of the previous section we allocated memory for the creation of the class instance.  In releases of the iOS SDK prior to iOS 5, good programming convention would have dictated that memory allocated to a class instance be released when the instance is no longer required.  Failure to do so, in fact, would have resulted in memory leaks with the result that the application would continue to use up system memory until it was terminated by the operating system.
  • 31. Cont…  Objective-C has provided similar functionality on other platforms but not for iOS.  That has now changed with the introduction of automatic reference counting in the iOS 5 SDK and it is not necessary to call the release method of an object when it is no longer used in an application.
  • 32. Cont..  the ARC avoids the necessity to call the release method of an object it is still, however, recommended that any strong outlet references be assigned nil in the viewDidUnload methods of your view controllers to improve memory usage efficiency. As a result, examples in this book will follow this convention where appropriate.
  • 33. Calling Methods and Accessing Instance Data  We have now created a new class called BankAccount. Within this new class we declared some instance variables to contain the bank account number and current balance together with some instance methods used to set, get and display these values.  In the preceding section we covered the steps necessary to create and initialize an instance of our new class.  The next step is to learn how to call the instance methods we built into our class.
  • 34. Cont…  The syntax for invoking methods is to place the object pointer variable name and method to be called in square brackets ([]).  For example, to call the displayAccountInfo method on the instance of the class we created previously we would use the following syntax: [account1 displayAccountInfo];
  • 35. Objective-C and Dot Notation  hose familiar with object oriented programming in Java, C++ or C# are probably reeling a little from the syntax used in Objective-C.  They are probably thinking life was much easier when they could just use something called dot notation to set and get the values of instance variables.  The good news is that one of the features introduced into version 2.0 of Objective-C is support for dot notation.
  • 36. Cont…  Dot notation involves accessing an instance variable by specifying a class instance followed by a dot followed in turn by the name of the instance variable or property to be accessed: double balance1 = account1.accountBalance;
  • 37. How Variables are Stored  When we declare a variable in Objective-C and assign a value to it we are essentially allocating a location in memory where that value is stored.  Take, for example, the following variable declaration: int myvar = 10;
  • 38. An Overview of Indirection  Indirection involves working with pointers to the location of variables and objects rather than the contents of those items.  In other words, instead of working with the value stored in a variable, we work with a pointer to the memory address where the variable is located.  Pointers are declared by prefixing the name with an asterisk (*) character.  For example to declare a pointer to our myvar variable we would write the following code: int myvar = 10; int *myptr;
  • 39. Cont..  he address of a variable is referenced by prefixing it with the ampersand (&) character. We can, therefore, extend our example to assign the address of the myvar variable to the myptr variable: int myvar = 10; int *myptr;
  • 40. Indirection and Objects  So far in this chapter we have used indirection with a variable. The same concept applies for objects. In previous chapters we worked with our BankAccount class. When doing so we wrote statements similar to the following: BankAccount *account1; BankAccount *account1 = [[BankAccount alloc] init];
  • 41. Indirection and Object Copying  Due to the fact that references to objects utilize indirection it is important to understand that when we use the assignment operator (=) to assign one object to another we are not actually creating a copy of the object.  Instead, we are creating a copy of the pointer to the object. Consider, therefore, the following code: BankAccount *account1; BankAccount *account2; BankAccount *account1 = [[BankAccount alloc] init]; account2 = account1;
  • 42. Creating the Program Section  The last stage in this exercise is to bring together all the components we have created so that we can actually see the concept working.  The last section we need to look at is called the program section.  This is where we write the code to create the class instance and call the instance methods.  Most Objective-C programs have a main() routine which is the start point for the application. The following sample main routine creates an instance of our class and calls the methods we created:
  • 43. EX… Int main (int argc, const char * argv[]) { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; // Create a variable to point to our class instance BankAccount *account1; // Allocate memory for class instance account1 = [BankAccount alloc]; // Initialize the instance account1 = [account1 init]; // Set the account balance [account1 setAccountBalance: 1500.53];
  • 44. // Set the account number [account1 setAccountNumber: 34543212]; // Call the method to display the values of // the instance variables [account1 displayAccountInfo]; // Set both account number and balance [account1 setAccount: 4543455 andBalance: 3010.10]; // Output values using the getter methods NSLog(@"Number = %i, Balance = %f", [account1 getAccountNumber], [account1 getAccountBalance]); [pool drain]; return 0;}
  • 45. Making your first iPhone App
  • 46. Starting Xcode 4
  • 47.  If you do not see this window, simply select the Window -> Welcome to Xcode menu option to display it.  From within this window click on the option to Create a new Xcode project. This will display the main Xcode 4 project window together with the New Project panel where we are able to select a template matching the type of project we want to develop:
  • 48.  Begin by making sure that the Application option located beneath iOS is selected.  The main panel contains a list of templates available to use as the basis for an application.  The options available are as follows: Master-Detail Application  Used to create a list based application. Selecting an item from a master list displays a detail view corresponding to the selection.  The template then provides a Back button to return to the list.  You may have seen a similar technique used for news based applications, whereby selecting an item from a list of headlines displays the content of the corresponding news article.  When used for an iPad based application this template implements a basic split-view configuration.
  • 49. Cont.. OpenGL Game  As discussed in iOS 5 Architecture and SDK Frameworks, the OpenGL ES framework provides an API for developing advanced graphics drawing and animation capabilities.  The OpenGL ES Game template creates a basic application containing an OpenGL ES view upon which to draw and manipulate graphics and a timer object.
  • 50. Cont.. Page-based Application  Creates a template project using the page view controller designed to allow views to be transitioned by turning pages on the screen. Tabbed Application  Creates a template application with a tab bar.  The tab bar typically appears across the bottom of the device display and can be programmed to contain items that, when selected, change the main display to different views.
  • 51. Cont… Utility Application  Creates a template consisting of a two sided view. For an example of a utility application in action, load up the standard iPhone weather application.  Pressing the blue info button flips the view to the configuration page. Single View Application  Creates a basic template for an application containing a single view and corresponding view controller. Empty Application  The most basic of templates this creates only a window and a delegate.
  • 52. Create new project…
  • 53. the new project has been created the main Xcode window will appear as illustrated in Figure
  • 54. Creating the iOS App User Interface
  • 55.  The right hand panel, onc e displayed, will appear as illustrated in Figure
  • 56. Changing Component Properties ◦ With the property panel for the View selected in the main panel, we will begin our design work by changing the background color of this view. ◦ Begin by making sure the View is selected and that the Attribute Inspector (View -> Utilities -> Show Attribute Inspector) is displayed in the right hand panel. ◦ Click on the gray rectangle next to the Background label to invoke the Colors dialog. ◦ Using the color selection tool, choose a visually pleasing color and close the dialog. You will now notice that the view window has changed from gray to the new color selection.
  • 57. Adding Objects to the User Interface  The next step is to add a Label object to our view.  To achieve this, select Cocoa Touch -> Controls from the library panel menu, click on the Label object and drag it to the center of the view.  Once it is in position release the mouse button to drop it at that location:
  • 58. Drang & Drop label from Data control panel
  • 59.  double click on the text in the label that currently reads “Label” and type in “Hello World”. At this point, your View window will hopefully appear as outlined in Figure (allowing, of course, for differences in your color and font choices):
  • 60. Out put