Transcript Introduction to Objective-C

Introduction to Objective-C
and
iPhone Development
1
Introduction
• Objective-C is implemented as set of extensions
to the C language.
• It's designed to give C a full capability for objectoriented programming, and to do so in a simple
and straightforward way.
• Its additions to C are few and are mostly based
on Smalltalk, one of the first object-oriented
programming languages.
2
Why Objective C
• Objective-C incorporates C, you get all the benefits of C
when working within Objective-C.
• You can choose when to do something in an objectoriented way (define a new class, for example) and when
to stick to procedural programming techniques (define a
struct and some functions instead of a class).
• Objective-C is a simple language. Its syntax is small,
unambiguous, and easy to learn
• Objective-C is the most dynamic of the object-oriented
languages based on C. Most decisions are made at run
time.
3
Object-Oriented Programming
• The insight of object-oriented programming is to
combine state and behavior, data and
operations on data, in a high-level unit, an
object, and to give it language support.
• An object is a group of related functions and a
data structure that serves those functions. The
functions are known as the object's methods,
and the fields of its data structure are its
instance variables.
4
The Objective-C Language
• The Objective-C language is fully
compatible with ANSI standard C
• Objective-C can also be used as an
extension to C++.
• Although C++ itself is a Object-Oriented
Language, there are difference in the
dynamic binding from Objective-C
5
Objective-C Language (cont.)
• Objective-C source files have a “.m”
extension
• “.h” file is the interface file
• For example:
– main.m
– List.h (Interface of List class.)
– List.m (Implementation of List class.)
6
ID
• “id” is a data type used by Objective-C to
define a pointer of an object (a pointer to
the object’s data)
• Any type of object, as long as it is an
object, we can use the id data type.
• For example, we can define an object by:
id anObject;
• nil is the reserved word for null object
7
Dynamic Typing
• “id” data type has no information about the
object
• Every object carries with it an isa instance
variable that identifies the object's class,
that is, what kind of object it is.
• Objects are thus dynamically typed at run
time. Whenever it needs to, the run-time
system can find the exact class that an
object belongs to, just by asking the object
8
Messages
• To get an object to do something, you
send it a message telling it to apply a
method. In Objective-C, message
expressions are enclosed in square
brackets
[receiver message]
• The receiver is an object. The message is
simply the name of a method and any
arguments that are passed to it
9
Messages (cont.)
• For example, this message tells the myRect
object to perform its display method, which
causes the rectangle to display itself
[myRect display];
[myRect setOrigin:30.0 :50.0];
• The method setOrigin::, has two colons, one for
each of its arguments. The arguments are
inserted after the colons, breaking the name
apart
10
Polymorphism
• Each object has define its own method but for
different class, they can have the same method
name which has totally different meaning
• The two different object can respond differently
to the same message
• Together with dynamic binding, it permits you to
write code that might apply to any number of
different kinds of objects, without having to
choose at the time you write the code what kinds
of objects they might be
11
Inheritance
• Root class is NSObject
• Inheritance is cumulative.
A Square object has the
methods and instance
variables defined for
Rectangle, Shape,
Graphic, and NSObject,
as well as those defined
specifically for Square
12
Inheritance (cont.)
• Instance Variables: The new object contains not only the
instance variables that were defined for its class, but
also the instance variables defined for its super class, all
the way back to the root class
• Methods: An object has access not only to the methods
that were defined for its class, but also to methods
defined for its super class
• Method Overriding: Implement a new method with the
same name as one defined in a class farther up the
hierarchy. The new method overrides the original;
instances of the new class will perform it rather than the
original
13
Class Objects
• Compiler creates one class object to
contain the information for the name of
class and super class
• To start an object in a class:
id myRectx; myRect = [[Rectangle alloc]
init];
• The alloc method returns a new instance
and that instance performs an init method
to set its initial state.
14
Defining a Class
• In Objective-C, classes are defined in two
parts:
– An interface that declares the methods and
instance variables of the class and names its
super class
– An implementation that actually defines the
class (contains the code that implements its
methods)
15
The Interface
• The declaration of a class interface begins
with the compiler directive @interface and
ends with the directive @end
@interface ClassName : ItsSuperclass
{
instance variable declarations
}
method declarations
@end
16
Declaration
• Instance Variables
float width;
float height;
BOOL filled;
NSColor *fillColor;
• Methods:
• names of methods that can be used by class objects,
class methods, are preceded by a plus sign
+ alloc
• methods that instances of a class can use, instance
methods, are marked with a minus sign:
- (void) display;
17
Declaration (cont.)
• Importing the Interface: The interface is
usually included with the #import directive
#import "Rectangle.h"
• To reflect the fact that a class definition builds on
the definitions of inherited classes, an interface
file begins by importing the interface for its super
class
• Referring to Other Classes: If the interface
mentions classes not in this hierarchy, it must
declare them with the @class directive:
@class Rectangle, Circle;
18
The Implementation
#import "ClassName.h"
@implementation ClassName
method definitions
@end
- makeIdenticalTwin
{
if ( !twin )
{
twin = [[Sibling alloc] init];
twin->gender = gender;
twin->appearance = appearance;
}
return twin;
}
19
Implementation (cont.)
Example:
@interface Worker : NSObject
{
char *name;
@private
int age;
char *evaluation;
@protected
id job;
float wage;
@public
id boss;
}
20
Implementation (cont.)
- promoteTo:newPosition
{
id old = job;
job = newPosition;
return old;
}
21
GCC and Objective-C
• Objective-C is layered on top of the C language
• iPhone & iPad “native” applications are written in
Objective C
• The Apple dev kit for Objective-C is called
“Cocoa”
• Can be written on any computer that has GCC
plus “GNUstep” plug-in
• Apple computers have all of this pre-installed,
and also have an iPhone simulator in the XCode
IDE
22
Tools
• Apple: pre-installed with the Cocoa frameworks
– XCode or GCC in terminal window
• Ubuntu: GnuStep is a free clone of Cocoa
–
–
–
–
–
–
sudo aptget
install buildessentials
gobjc gnustep
gnustepmake
gnustepcommon
libgnustepbasedev
• Windows: http://www.gnustep.org/
23
File Overview
• Source code files have a .m extension
• Header files have a .h extension
• You can use gcc to compile in the same
way as C code
• But, you will need to add the Cacoa or
GNUStep frameworks to the build.
24
Example: Hello World
#import <Foundation/Foundation.h>
int main (int argc, const char * argv[]) {
NSAutoreleasePool * pool =
[[NSAutoreleasePool alloc] init];
// insert code here...
NSLog(@"Hello, World!");
[pool drain];
return 0;
}
NSLog() is equivalent to a C printf()
Very similar to C
C programs are valid in Objective-C
25
Compiling Hello World in Xcode
(Mac)
• File->New Project
– Mac OS X category – Select Application
– Command Line Tool
– Type - “Foundation”
• Name project helloworld and choose folder
• Edit helloworld.m and paste in our example over the top of
the default. The default code is this sample program.
• Save.
• Note that Foundation.framework has been included for us
already
• “Build and run”.
• The debugger console should show “Hello World”
26
Compiling Hello World on Terminal
(Mac)
• Write hello.m using a plain text editor
• To comple type:
gcc – framework Foundation hello.m –o hello
• Foundation brings in the Foundation framework
(Cocoa) which
• bundles together a set of dependencies (header
files and libraries). You will need this every time
we compile Objective C code.
• Type: ./hello will run the program in the terminal
• Note: this approach is fine for early examples
but the iPhone applications will be much easier
to build in XCode.
27
Intro to HelloWorld
• Objective-C uses a string class similar to the
std::string or Java string. It is called NSString.
• Constant NSStrings are preceded by @ for
example: @”Hello World”
• You will notice that NSLog() also outputs time
and date and various extra information.
• NSAutoreleasePool* pool =[[NSAutoreleasePool
• alloc] init]; allocates a lump of memory
• Memory must be freed with [pool drain];
28
Example 2
#import <Foundation/Foundation.h>
int main(int argc, const char* argv[]) {
NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];
NSLog (@”Hello World”);
int undergrads = 120;
int postgrads = 50;
int students = undergrads + postgrads;
NSLog (@”Now featuring...\n %i Computer Science students”, students);
[pool drain];
return 0;
}
29
Some things to note
• No line break needed at end of NSLog
statements.
• NSString constants use C-style variables.
• Test this program to see results.
30
@interface
@interface ClassName : ParentClassName
{
declare member variable here;
declare another member variable here;
}
declare method functions here;
@end
•
•
•
•
Equivalent to C class declaration
Goes in header (.h) file
Functions outside curly braces
Don’t forget the @end tag
31
@implementation
#import <Foundation/Foundation.h>
#include "ComputerScience.h“
@implementation ClassName
define method function here;
define another method function here;
define yet another method function here;
@end
● Equivalent to C class function definitions
● Goes in source (.m) file
● Don't forget the @end tag
32
Example 3: ComputerScience.h
@interface ComputerScience : NSObject
{
int mUndergrads;
int mPostgrads;
}
-(void) print;
-(void) setUndergrads: (int) undergrads;
-(void) setPostgrads: (int) postgrads;
@end
33
Some things to note
• NSObject is the “root” object in Objective-C
• No direct access to instance variables so we write
some get/set “instance methods”
• Instance methods (affect internal state of class)
are preceded with a minus sign
• “Class methods” (higher level functions) are
preceded with a plus sign e.g. create new class
• Method return type in parentheses
• Semicolon before list of parameters
• Parameter type in parenthesis, followed by name
34
Example 3: ComputerScience.m
#include “ComputerScience.h”
@implementation ComputerScience
-(void) print {
int totalStudents = mUndergrads + mPostgrads;
NSLog (@”Total students in CompSci = %i”,
totalStudents);
}
-(void) setUndergrads: (int) undergrads {
mUndergrads = undergrads;
}
-(void) setPostgrads: (int) postgrads {
mPostgrads = postgrads;
}
@end
35
Some things to note
• Note prefix minus sign
• Very similar to C
• Same format as with the interface
36
Example2: main.m
#import <Foundation/Foundation.h>
#include “ComputerScience.h”
int main(int argc, char* argv[]) {
NSAutoreleasePool* pool = [[NSAutoreleasePool alloc]
init];
ComputerScience* ituCompSci; // pointer
ituCompSci = [ComputerScience alloc]; // allocate memory
ituCompSci = [ituCompSci init]; // initialize
[ituCompSci setUndergrads: 120]; // apply method to
instance
[ituCompSci setPostgrads: 2000];
[ituCompSci print];
[ituCompSci release];
[pool drain];
return 0;
}
37
Some things to note
• Applying methods to instance format:
[receiver message];
• Semi-colon for variables or values passed
to methods
• [pool drain] etc. are also applying
methods.
• Built-in messages; alloc, init, release.
38
Some other things to note
• alloc is equivalent to C++ new but it also
zeros all variables
• init should be applied to an instance before
use
• These are often combined in shorthand:
ComputerScience* ituCompSci =
[[ComputerScience alloc] init];
• There is no garbage collection on the
iPhone, so we should release all of our
instance memory.
39
To compile example 3
•
•
•
•
Create a project in Xcode
Delete the original main.m
Add existing files to the project
Compile and run!
40
Data Structures
• Objective-C arrays are similar to C arrays, but
you can initialize whole array in a list.
• Or just a few indices of the array. The rest are
set to 0.
• Or mix and match; the example will create an
array of size [8].
int values[3] = { 3, 4, 2 };
char letters[3] = { 'a', 'c', 'x' };
float grades[100] = {10.0,11.2,1.1};
int array[] = {[3]=11,[2]=1,[7]=0};
41
Multi-dimensional Arrays
• Can be initialized by using subset notation with
braces. Note no comma after second subset.
• Subset braces are optional, the compiler will fill
in blanks where it can as with 1D arrays.
int array[2][3] = {
{ 0, 3, 4},
{ 1, 1, 1}
};
int array[2][3] = {0, 3, 4, 1, 1, 1};
42
Arrays and Functions
• Arrays can be passed as arguments to functions.
• This function will print every integer in an array but it needs
to also be told how long the array is (arrayLength).
• Statements with hard-coded indices such as array[4] are
potentially dangerous.
void function(int array[], int arrayLength) {
int fourthValue = array[4];
for (int i = 0; i < arrayLength; i++) {
NSLog(@”%i”, array[i]; }
}
43
Structs
• Similarly the Objective C “struct” can be
• initialized in one go.
• Use the '.' member notation or just use
values in the correct order or use some
values. 'unknown.'
• In the following example we explicitly
define the last member, but the others are
undefined.
44
Structs
struct ComputerScience {
int BSYears;
int PhDYears;
int WellSpentYears;
};
struct ComputerScience myCareer = {
.BSYears = 3, .PhDYears = 3, .WellSpentYears = 6
};
struct ComputerScience poorLifeDecisions = { 3, 8, 3 };
struct ComputerScience unknown = { 3 };
struct ComputerScience andFurtherMore = { .WellSpentYears
= 0 };
45
Declare+Define a Struct in One
• Similar to the older C-style notation.
• The example will declare a coffee order
struct and immediately define an instance
called “complexityGroup”.
struct coffeeOrder {
int Plain;
int DoubleEspresso;
} complexityGroup = { 7, 4 };
46
Fitting into limited memory: Bit fields
• To work on devices with memory limitations we
can manually define the bit size of variables.
• Using a struct, all of the members are packed
together efficiently.
• The next example divides a 16-bit unsigned
integer into 3 on/off bit flags, a 10-bit number
and a 3-bit number.
• Note that it is valid to use Boolean operations on
single bit variables.
47
Fitting into limited memory: Bit fields
struct AlarmPanelStruct {
unsigned int DoorAlarmTriggered:1;
unsigned int WindowAlarmTriggered:1;
unsigned int TrapdoorAlarmTriggered:1;
unsigned int AdministratorsID:10;
unsigned int AlarmKeyCode:3;
};
struct AlarmPanelStruct lab;
lab.AlarmCode = 1;
lab.DoorAlarmTriggered = 0;
if (DoorAlarmTriggered) ...
48
Fitting into limited memory: Unions
• Union data structures allow ambiguity.
• Useful for allowing one storage area to hold different
variable types.
• Can only hold one of the variables at a time.
• Must be careful to ensure retrieval type matches last type
stored.
• Might come in handy for storing lists of “data” that might be
of different types.
• The next example gives ones potentially practical use;
• A series of recordings store ‘Data.’
• The struct has a char to indicate the type of data recorded
in Data.
49
Fitting into limited memory: Unions
union OneOfTheFollowing {
char Letter;
int CountOf;
float Average;
};
OneOfTheFollowing lastSpaceOnThePhone;
lastSpaceOnThePhone.Letter = 'a';
lastSpaceOnThePhone.CountOf = 1;
struct RecordedData {
char* Name;
union {
float RealNumber;
int Integer;
char Letter;
} Data; // immediately defines an instance
char TypeOfData;
} arrayOfRecordedData[100];
50
Simulated iOS Apps
•
•
•
•
•
•
•
•
Relies heavily on the XCode IDE.
iPhone and iPad Simulator program is a free add-on for Xcode. You
just need a Mac computer to develop an iOS app.
Running or testing apps on an actual device is not free (~100
USD/year).
The process of deploying an app to a device is quite involved.
1. Software set-up
2. Developer sign-up
3. Member sign-up
4. Certificate request
Software comes as one bundle
Latest Xcode plus Simulators
Apple Organizer
GUI designer
51
Something to note!
• You can program for either the iPhone or
the iPad or both in the latest XCode.
• If you are going to do the examples for
both simultaneously be aware that there
are two sets of .h and .m files (one for
each).
52
Frameworks
• UIKit.framework for developing standard iOS GUIs
(buttons etc.)
• UITextField (user-entered text that brings up the
keyboard)
• UIFont
• UIView
• UITableView
• UIImageView
• UIImage
• UIButton (a click-able button)
• UILabel (a string of text on-screen)
• UIWindow (main Window on iPhone)
53
iOS programming
• Event driven framework
• Interface Designer has some extra macros for
the code that act like hooks to variables;
– IBAction - trigger events like mouse clicks
– IBOutlet - captures outputs from events
• These tags are not compiled (don't affect the
code) but sit as an extra before variables that
the Interface Designer can see.
54
Start a New XCode iOS Project
• New Project → iPhone/iPad OS
• Navigation-Based - “navigation controller” as
used in Contacts app.
• OpenGL ES - cut-down OpenGL
• Tab Bar – app in style of iPod app.
• Utility – Flipside app in style of stock quote app.
• View-Based – single view that you draw into and
display to screen.
• Window-Based – basic app with a main
window. (we will use this one for examples.)
55
Try Out - Hello World
• Watch the Hello World tutorial and build
your first iPhone application.
• The tutorial can be found at:
http://www.youtube.com/watch?v=lRt5vEpueQ
56
End of Lecture 1
• Next time, we will be doing more Object-C
programming and building more iPhone
applications.
• Make sure to practice with the “Hello
World” application before next week so
you can move forward with more complex
concepts and programming methods.
57