Properties description in objective c

Brief Description of Properties In Objective C

Before going to the depth of Object Oriented World First we go through brief explanation of property in objective c. In general Properties are used to encapsulate the data behind the instance variables. Encapsulation means just way of data hiding.

You can make the property 

readonly,readwrite,retain,assign,copy,strong,weak,atomic,non-atomic,getter=method,setter=method.

Example:

In .h file:

@interface Student

@property NSInteger *StudentID;

In .m (implementation) file:

@implementation Student

Student *student1=[[Student alloc]init];

Do you know that getter method are those which return a value each time when it is called.

-(NSInteger)StudentID

{

Return _StudentID; //return value of instance variables

}

-(void)setStudentID:(int)SID

{

_StudentID=SID;

}

 These are the getter and setter methods you can write explicitly but now xcode do it for you just with keyword @synthesize

@synthesize StudentID=_StudentID;

@Synthesize Property=_Instance variable;

// you can call with same name as property name but you can use the different name for instance variable but that is not the good idea.

Xcode compiler create automatically getter and setter method for you.

NSLog(@”The Student ID is:%@”,student1.StudentID);

Now we go through ReadOnly property

@property(readonly) NSString *StudentID;

Readonly means property will not include setter method or Setter method does not work.

(NSInteger)StudentID

{

Return 12;

}

How the Properties are called?

Properties are called by dot syntax.

Example:

 Object.PropertyName

Student1.StudentID=101;

NSInteger *integer=student1.StudentID;

You can print integer by using NSLog function.

When you try to set value with dot notation then it shows the compile error.

ReadWrite is By default you do not need to specify explicitly or if you write by fault then its meaning is same.

@property(readwrite) NSString *StudentName;

@property NSString *StudentName; //It is equivalent to above statement.

Retain property  

When there requires save of old values then there is need for retain case property.

@property(retain) NSString *StudentID;

You need to only change the setter method that is

-(void)setStudentID:(NSString *)StudentID

{

If(oldstudentid==StudentID)

{

Return ;

}

Student1=oldstudentid;

oldstudentid=[StudentID retain];

[oldstudentid release];

}

If the old value is equal to same new value then first value release the object before oldstudentid retain it.

Copy Property

When you want to set NSMutable value use copy accessor then there shows warning regarding setter method

Example:

@property(copy) NSString *StudentName;

NSMutableString *studentname=@”suraj”;

Student1.StudentName=studentname;

Above shows unaffected to the studentname property there need change in setter method.

Assgin property

Assign property stores the value directly to non-pointer attribute rather then retain or copy the attributes.

@property(assign) NSInteger yearofjoiningcollege;

It is generally used for primititive types like integer and float.

Getter=method

If you want to get properties with different method names then use this attributes.

@property(getter=isStudying) bool *studentStudy;

Setter=method

It is opposite to the getter=method.