Creating Protected and Private Variables in Objective-C Class

Java and other similar languages, including ActionScript, offer avery simple syntax for created protected and private variables.Protected meaning that any subclass can see and manipulate thevariable or function. Private methods and variables will not beaccessible
to the subclasses. The syntax is to simply adda

protected

ora

private

statementbefore
a variable or function.

protected function someMethod():void { ... }

private var somePrivateVar:int;

Easy, each is clearly defined as such. My experience withObjective-C in iOS has not offered that simplicity.

Protected and Private without the

@synthesize

There is an easy way to create protected and private variables fora class. This method does not utilizethe

@synthesize

directivethat is
part of Xcode. So memorymanagement is completely up to you. I findthis method works very well with variables that are not descendantsof

NSObject

becausethere
is no memory management needed.

The interface file (

class.h

)and inside the

@interface

declaration,add
a

@protected

or

@private

.Anything
that follows the line will be protected or privaterespectively. The key is not to addthe

@property

linewith the description for the variable,
northe

@synthesize

inthe implementation file (

class.m

).

@interface PhotoViewer : UIView {

NSArray *images; // protected
by default

@protected

int index; // protected in class

@private

UIImageView *imageView; // will be private in class

UIView *customView; // will be private in class

}

@end

Subclasses of this sample

PhotoViewer

classwill be able to see the

index

variable,however
they will not be able to seethe

imageView

northe

customView

.Additionally,
because there is no

@synthesize

atplay here, retaining variables by the class will have to be donemanually. So setting the

imageView

wouldlook
something like

@implementation

- (id)initWithFrame:(CGRect)frame {

self = [super initWithFrame:frame];

if (self) {

imageView = [[UIImageView alloc] init]; //
retain count of1

}

return self;

}

- (void)dealloc {

[imageView release];

[super dealloc];

}

@end

No need to go over memorymanagement in any further depth, suffice it tosay, the

imageView

inthe
example above has been

alloc

dso it must be released in the

dealloc

otherwisethe
class will run into memory issues and not get released.

Everyone Needs to Know

Static variables. Thinking you can shorthand this and createvariables directly in the implementation file would be correct. Itworks. However, creating variables in the implementation block willcreate a static variable. Static variables, are of course, sharedwith
every instance of the class. So using the example class above,if we created

index

inthe

@implementation

partof
the file, every time a

PhotoViewer

wascreated and set the

index=
0;

, every instance would havean

index

equalto

0

.

This can be really useful for many things, especially games wherean enemy ship may need to know how many other ships there are. Soif we used the class above and created a static variable, it wouldlook like

@implementation

int numberOfPhotoViewers = 0; // static variable forPhotoViewer count

- (id)initWithFrame:(CGRect)frame {

self = [super initWithFrame:frame];

if (self) {

imageView = [[UIImageView alloc] init];

numberOfPhotoViewers++;

}

return self;

}

- (void)dealloc {

[imageView release];

[super dealloc];

}

@end

Not complicated, however it could cause a few problems if that wasnot expected behavior... and to me, was not.