Introduction to Objective-C

Objective-C is the language used in iOS development. It is an object-oriented language, making it straightforward for programmers who already have knowledge of object-oriented languages.

Interface and Implementation

Files completed in Objective-C are called interface files, and the definitions of these files are called implementation files.

A simple interface file MyClass.h will look like this:

@interface MyClass:NSObject{ 
// Class variable declarations
}
// Class property declarations
// Class method and declarations
@end

The implementation file MyClass.m is shown below:

@implementation MyClass
// Class method definitions
@end

Creating Objects

Objects are created as follows:

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

Methods

Methods in Objective-C are declared as follows:

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

An example is shown below:

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

You might wonder what "andBreadth" is; it's an optional string that helps us read and understand the method, especially when it's called.

To call this method within the same class, we use the following statement:

[self calculateAreaForRectangleWithLength:30 andBreadth:20];

As mentioned earlier, "andBreadth" helps us understand that breadth is 20. "Self" is used to specify that it's a class method.

Class methods can be accessed directly without creating an object. They have no variables associated with the object. An example is:

+(void)simpleClassMethod;

It can be accessed using the class name (assuming MyClass as the class name) as follows:

[MyClass simpleClassMethod];

Instance methods can only be accessed after creating an object of the class, where memory is allocated for instance variables. An instance method looks like this:

-(void)simpleInstanceMethod;

After creating an object of the class, it can be accessed as follows:

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

Important Data Types in Objective-C

Printing Logs

NSLog is used to print a statement, which will be printed in the device log and the console in debug mode.

For example:

NSLog(@"");

Control Structures

Most control structures are the same as in C and C++, with a few additional clauses.

Properties

Properties are used to access variables of a class from outside the class.

For example:

@property (nonatomic, strong) NSString* myString

Accessing Properties

Properties can be accessed using the dot operator. To access the previous property, you can do the following:

self.myString = @"Test";

Alternatively, you can use the set method as follows:

[self setMyString:@"Test"];

Categories

Categories are used to add methods to existing classes. This way, you can add methods to a class without modifying its implementation file. A sample category for MyClass looks like this:

@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, where the former is a mutable array and the latter is an immutable array. Examples are:

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

initWithObjects:@"firstObject", nil];

Dictionary

NSMutableDictionary and NSDictionary are dictionaries used in Objective-C, where the former is a mutable dictionary and the latter is an immutable dictionary, as shown below:

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