iOS - Objective C

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Introduction

The language used in iOS development is objective C. It is an object oriented language and hence it would easy for those who have some background in object oriented language programming.

Interface and Implementation

In objective C the file where the declaration of class is done is called the interface file and the file where the class is defined is called the implementation file.

A simple interface file MyClass.h would look like the following.

@interface MyClass:NSObject{ 
// class variable declared here
}
// class properties declared here
// class methods and instance methods declared here
@end

The implementation file MyClass.m would be like follows

@implementation MyClass
// class methods defined here
@end

Object Creation

Object creation is done as follows

MyClass  *objectName = [[MyClass alloc]init] ;

Methods

Method is declared in objective C as follows

-(returnType)methodName:(typeName) variable1 :(typeName)variable2;

An example is shown below

-(void)calculateAreaForRectangleWithLength:(CGfloat)length 
andBreadth:(CGfloat)breadth;

You might be wondering what the andBreadth string for; actually its optional string which helps us read and understands the method easier especially at the time of calling. To call this method in the same class we use the following statement

[self calculateAreaForRectangleWithLength:30 andBreadth:20];

As said above the use of andBreadth helps us understand that breath is 20. Self is used to specify it's a class method.

Class method

Class methods can be accessed directly without creating objects for the class. They don't have any variables and objects associated with it. An example is shown below.

+(void)simpleClassMethod;

It can be accessed by using the class name (let's assume the class name as MyClass) as follows.

[MyClass simpleClassMethod];

Instance methods

Instance methods can be accessed only after creating an object for the class. Memory is allocated to the instance variables. An example instance method is shown below.

-(void)simpleInstanceMethod; 

It can be accessed after creating an object for the class as follows

MyClass  *objectName = [[MyClass alloc]init] ;
[objectName simpleInstanceMethod];

Important data types in Objective C

S.N.Data Type
1NSString
It is used for representing a string
2CGfloat
It is used for representing a floating point value (normal float is also allowed but it's better to use CGfloat)
3NSInteger
It is used for representing integer
4BOOL
used for representing Boolean(YES or NO are BOOL types allowed )

Printing logs

NSLog - used for printing a statement. It will be printed in device logs and debug console in release and debug modes respectively.

Eg: NSlog(@"");

Control Structures

Most of control structures are same as in C and C++ except for a few additions like for in statement.

Properties

For an external class to access class variables properties are used

Eg: @property(nonatomic , strong) NSString *myString;

Accessing Properties

You can use dot operator to access properties. To access the above property we will do the following.

self.myString = @"Test";

You can also use set method as follows.

[self setMyString:@"Test"];

Categories

Categories are use to add methods to existing classes. By this way we can add method to classes for which we don't have even implementation files where the actual class is defined. A sample category for our class is as follows.

@interface MyClass(customAdditions)
- (void)sampleCategoryMethod;
@end

@implementation MyClass(categoryAdditions)

-(void)sampleCategoryMethod{
   NSLog(@"Just a test category");
}

Arrays

NSMutableArray and NSArray are the array classes used in objective C. As the name suggests the former is mutable and latter is immutable. An example is shown below.

NSMutableArray *aMutableArray = [[NSMutableArray alloc]init];
[anArray addObject:@"firstobject"];
NSArray *aImmutableArray = [[NSArray alloc]
initWithObjects:@"firstObject",nil];

Dictionary

NSMutableDictionary and NSDictionary is the dictionary classes used in objective C. As the name suggests the former is mutable and latter is immutable. An example is shown below.

NSMutableDictionary*aMutableDictionary = [[NSMutableArray alloc]init];
[aMutableDictionary setObject:@"firstobject" forKey:@"aKey"];
NSDictionary*aImmutableDictionary= [[NSDictionary alloc]initWithObjects:[NSArray arrayWithObjects:
@"firstObject",nil] forKeys:[ NSArray arrayWithObjects:@"aKey"]];


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