Presentation 4th

More On Variable,Categories and Protocols

Chhorn Chhaly

Leang Bunrong

Cheng Udam

Kan Vichhai

Srou Chanthorn

Em Vy

Seth Sambo

Chea Socheat

Content1. More on Variables and Data Types

Initialize Objects

Scoped Revisited More on properties, Synthesized Accessors, and Instance Variables

Global Variable

Static Variable

Enumerated Data Types

The typedef statement

Data Type Convers

• Categories and Protocols

Categories

Class Extensions

Protocols and Delegation

Composite Object

Initializing Objects

• We initializing object by calling “init” method

• For example Fraction *f=[[Fraction alloc]init];

• The example above we just get an Object that has nothing or field value

• If we want to initialize object with many fields value, we have to create our custom method to initialize object

Objective-C Java

Initializing Objects

• The method initWithNumerator:(int)n withDenominator:(int)d is the custom method to initializing object

• All initializing methods must start with word “init…..”

• Self=[super init] means the super class calls “init” method to initialize for current object

• But it just an object without any fields value

• After that line we see that we initialize _numerator and _denomitor

• Then we return “self” that fulfill of object with field values

Variable Scope

In Objective-C, a variable has been declared it may or may not be accessible to other sections of the program code. This accessibility depends on where and how the variable was declared and where the code is that needs to access it. This is know as variable scope.

Local Variables

Variables that are declared inside a function or block are called local variables. They can be used only by statement that are inside that function or block of code. Local variable are not known to functions outside their own.Example:

Objective-C:-(void) sum:(int) x secondP:(int) y {

int total;total = x+y;NSLog(@”Total: %i”, total);

}NSLog(@”Total: %i”, total); // illegal Total is now out of scope.

Java:public void sum(int x, int y){

int total;total = x+y;System.out.println(“Total: ” + total);

}System.out.println(“Total: ”+ total); // illegal Total is now out of scope.

Global VariablesGlobal variables are defined outside of a function, usually on top of the program. A global variable can be accessed by any function. That is, a global variable is

Objective-C#import <Foundation/Foundation.h>Int myVar = 321;Int main (int argc, conts char * argv[]){ @autoreleasepool{

NSLog(@”myVar = %i”, myVar); } return 0;}

The second file, named display.m contain the code for the displayit() function.

#import <Foundation/Foundation.h>extern int myVar; void displayit(){ NSLog(@”MyVar from different source file is i%”, myVar);}

JavaPublic class Global{ Int myVar = 321; public static void main (String args[]){

System.out.println(“myVar = ”+ myVar);}

void displayit(){ System.out.println(“myVar = ”+myVar); }}

Multiple Classes In .h file In the Models.h file we declare two classes

Multiple Classes in .h file(cont.)

Import Models.h we get two classes

Accessing static and non static field to category Models class(.h.m)

Accessing static and non static field to category Calling static field(check) and non static field(modelsfield) to MyCatagory.

Enumerated Data Types

• Enumerated Type : Is an user-defined type that is used in Objective-C to represent the

data that can be stored in one of several predefined values (all of them are int).

• What is it’s purpose : The purpose of enumerated types is to create specifically named

constants.

• Syntax : enum name_of_enumerator { element1, element2,…};

• enum : tell compiler to create enumeration

• name_of_enum : is the name to be assigned the enumeration

• element: field are the name that can be used to set variable

Enumerated Data Types

NOTE : • enumerators use numbers corresponding to the element

• By default the first value corresponds to 0, the second to 1 and so on

• It is also possible to specify the values used by each value name

enum temperatureTypes{ cold = 10, // (redefined up = 10) warm, // down will 11 (increment one from

previous) hot = 95, // (redefined left = 95) veryhot // right will 96 (increment one from

previous) };

Example

The Typedef Statement

• The Typedef Statement : allows the programmer to define one Objective-C type as

another.

• To define a new typedef :

• Write the statement as if a variable of the original type was being declared

• Where you would put the name of the variable (after the type), place the new type name.

• Prefix everything with typedef

The Typedef Statement

• Syntax:

• Example:

in this example above, define the name Counter to be equivalent to the Objective-C data type int.

The second line we declare variable to be type of Counter.

typedef DataType variable;

typedef int Counter;

Counter i, j;

Data Type Conversion

• Type casting is a way to convert a variable from one data type to another data type.

• In Objective-C when we evaluation of the two operands, type of the result is convert to the big size between the two operands automatically but except char, short int or of an enumarated data type they are converted to int.

• Example: Output

• Example:Output

Data Type Conversion (cont.)

• In Objective-C is almost the same with Java but still have a little bit different below:

• In Java long and short are data type but in Objective-C is not so it make a conversion different.

In Java:In Objective-C:

Categories Category is the best way to add more methods to class in objective – C language.

We can override method in base class but it is poor programming practice( duplicate functionalities of method when running time).

Name of category start with base class plus category name( BaseClassName+CategoryName) in import section.

.m

.h

class

Category

Categories

Syntax:

@interface ClassName (CategoryName)

//// methods declaration part

@end

Categories

Cateories Example:

MyModel class has only one method (ownMethod).

CategoriesCateories Example:

CategoryOfMyModel has one method (newMethod).

CategoriesCateories Example:

MyModel

-(void)ownMethod-(void)newMethod

Compile time

MyModel

-(void)ownMethod

MyModel+CategoryModel

-(void)newMethod

Class Extensions

• Class extension is a special case allows creating a category without a name

- when you define an unnamed category like this, you can extend the class by adding

additional instance variables and properties.

- This is not allowed for named categories.

Class Extensions Cont......

MyClass.h

MyClass.m

Class Extensions Count......

Main method

Protocol• protocol fully complete abstraction every method in protocol is abstract

• it is list the method name without body, it wait other class implement it and implement body to it.

• we use it to create the standard method for all classes use the same method when they implement protocol, it is look like interface in java.

• and it use for delegate also

syntax in objective c syntax in java

Protocol

• in objective divided two part of protocol @required and @optional

• @required it mean that we need to implement method when the class implements it.

• @optional it mean that we are not need to implement method when the class implements it, it is up to you.

syntax:

Protocol

• we can implement more than one protocol

• how to implement single and multiple implement protocol

• first we need to import protocol

single implementation in objective c Single implementation in java

Protocol

multiple implementation in objective c multiple implementation in java

Delegate

• Delegate allow one object send message to other object when an event happen

• We use delegate almost for event handler in IOS

• We can use delegate when we want it to do something when something happen in our program and raise it up.

• We almost use id for create a delegate

• We will raise it detail in later chapter that detail about the delegate

Composite Object• What is composite object?

A technique that a class consists of one ore more objects from other classes is call “Composite Object”.

Diagram above show you that ClassA has ClassB as its composite.

If ClassA is deleted then ClassB is also deleted as a result. But if ClassB is deleted ClassA will not be delete.

ClassA ClassB

Composite Object

• Example of composite object:

Composite Object

• Let Create other Square class that have Rectangle as its composite

Composite Object

• In our main.m file

Composition Object

• Let compare our code with java code:

Rectangle.java

Composite Object• Square.java

Composite Object

• Main.java

Composite Object

• The result of these two will output the same

Thank you