Tuesday, March 12, 2013

A few Objective-C kick start tips for C++ Developers

Here are a few things I as a C++ developer had to learn the hard way.


Basic Language Constructs

+ sign for static methods - sign for methods that require objects

For instance in C++ we do the following
public:
static void SomeMethod();

The objective-C equivalent would be

+(void) SomeMethod;

Similarly for non-static methods just change the + sign to -. They are called Instance Methods.

-(void) SomeNonStaticMethod;


You may also have noticed that the return type is enclosed in () parenthesis which was weird to me.

No private methods

Thats right, no method is private. You can have member variables or attributes private by using @private but methods cannot be private.

Method calling

In C++ we have, when we have to call a method; we do

myObj.MethodName();

In Objective-C, its totally changed. 

[myObj MethodName];

Tada! No Constructor

Yes, there is no such thing as constructor. All you do is call a native/built-in method alloc to create an object with default properties.

[MyClass alloc]; //Here is the object being created

But Objective-C developers have come up with something called initializers, so immediately after the object is created, an init method is called. Keep in mind that init is something developer has to create as a method that does some initialization work.

[ [MyClass alloc] init];

Weird asterisk * that reminds you of pointer will get on your nerve

Yes, that asterisk is for pointers. Every object reference is stored in pointers. 

So in C++ we create objects by simply writing the following code

MyClass MyObj = MyClass();

In Objective-C, you will have to write the following code
MyClass *MyObj = [ [ MyClass alloc ] init];

Project files

Objective-C has similar to .h/.cpp structure for class declaration and definition but its most often called .h/.m or .h/.mm (for Objective-C++)

Keyword interface is not what you think

interface keyword in Objective-C is used for class declarations.

C++ code
class MyClass

{

 public:

MyClass();

};

Objective-C will require you to write the following code for the above

@interface MyClass {

// non-static variables go here

}

- (MyClass*) init;

@end


Class definition or .m file

.m file or .cpp file counterpart in Objective-C would look something like this

@implementation MyClass { // Yes 'class' keyword is never seen

-(MyClass*) init  {

 if (self) {

// initialize self here

 }

return self;

}

@end



Thats all folks! There is more information on the topic which I intend to write in future blog posts. If you are a C++ developer and thinking about taking a nosedive into Objective-C, above mentioned things should be enough for you to brace for.

I would love to hear your comments. They help me understand how useful my postings are.