Objective C - How do I use initWithCoder method?

Question

I have the following method for my class which suppose to load the nib file and instantiate the object.

- (id)initWithCoder:(NSCoder*)aDecoder 
{
    if(self = [super initWithCoder:aDecoder]) 
 {
        // Do something
    }
    return self;
}

• so based on this init method how do u instantiate an object of this class?

• The init method requires a parameter (NSCoder), so what is this nscoder? how can i create it?

  MyClass *class = [[MyClass alloc] initWithCoder:aCoder];

Answer 1

The NSCoder class is used to archive/unarchive (marshal/unmarshal, serialize/deserialize) of objects.

This is a method to write objects on streams (like files, sockets) and being able to retrieve them later or in a different place.

I would suggest you to read http://developer.apple.com/library/mac/#documentation/cocoa/conceptual/Archiving/Archiving.html

Answer 2

You also need to define the following method as follows:

• (void)encodeWithCoder:(NSCoder *)enCoder { [super encodeWithCoder:enCoder];

  [enCoder encodeObject:instanceVariable forKey:INSTANCEVARIABLE_KEY];

  // Similarly for the other instance variables. .... }

And in the initWithCoder method initialize as follows:

• (id)initWithCoder:(NSCoder *)aDecoder {

  if(self = [super initWithCoder:aDecoder]) { self.instanceVariable = [aDecoder decodeObjectForKey:INSTANCEVARIABLE_KEY];

  // similarly for other instance variables .... }

  return self; }

You can initialize the object standard way i.e CustomObject *customObject = [[CustomObject alloc] init];