Singleton Object Creation

Singleton Object Creation

Defn:

In computer programming a singleton variable is a variable that is referred to only once.

Examples of where a variable might only be referenced once is as a dummy argument in a function call, or when its address is assigned to another variable which subsequently accesses its allocated storage.

Singleton variables sometimes occur because a mistake has been made – such as assigning a value to a variable and forgetting to use it later, or mistyping one instance of the variable name. Some compilers and lint-like tools flag occurrences of singleton variables.

Creating Singleton Object File:

In Sample Project we can add the file in Xcode tool.

File --> New --> File --> Choose Objective-C class --> Next --> 

class Name is "singleton" 
subclass is NSObject is Selected.

Next --> Finish.


singleton.h :

 #import <Foundation/Foundation.h>

@interface Singleton : NSObject

//Create the variables or objects.

@property(nonatomic,assign) float ad_height;

@property(nonatomic,assign) BOOL ads_removed,is_ipad;

@property(nonatomic, assign) CGRect banner_land;

@property(nonatomic, assign) CGRect banner_port;

@property(nonatomic,assign) UIInterfaceOrientation last_orient;

@property(nonatomic,assign) NSString *lastsss;

+(Singleton *)singleObj;  //class method

//-(void)Objsin;   //instance method

@end

singleton.m :

 #import "Singleton.h"

@implementation Singleton

@synthesize lastsss;

+(Singleton *)singleObj     //class Method

{

    

    static Singleton * single=nil;

    

    @synchronized(self)

    {

        if(!single)

        {

            single = [[Singleton alloc] init];

        }

    }

    return single;

}

-(void)Objsin      //instance method

{

    lastsss = @"aaa";

}

@end

SomeFile.h :

#import "Singleton.h"

@interface SomeFile : UIViewController

{

    Singleton *sobj;

}

SomeFile.m :

  //public method. Access from any page. Deallocate when app is closed.

-(void) viewwillappear method

{
   //reference to allocate

   sobj = [Singleton singleObj];    

   //Method calling
   [sobj Objsin];

    //Assign the values
    NSString *str= @"bb";

    sobj.lastsss = str;

    sobj.last_orient = [UIApplication sharedApplication].statusBarOrientation;

    sobj.banner_land = _bannerView.frame;   //CGRect(0, 0, 0, 0)

    sobj.banner_port = _bannerView.frame;   //CGRect(0, 0, 0, 0)

    sobj.ad_height = 40.0;

    sobj.is_ipad = (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad);    //YES or NO

    sobj.ads_removed = NO;

}

               (or)

 //private method. Access only this page. Deallocate when page is moved.

-(void) viewwillappear method

{

    //initiate memory allocation

    sobj = [[Singleton alloc]init];

    //Method calling

    [sobj Objsin]; 


    //Assign the values
    NSString *str= @"bb";

    sobj.lastsss = str;

    sobj.last_orient = [UIApplication sharedApplication].statusBarOrientation;

    sobj.banner_land = _bannerView.frame;   //CGRect(0, 0, 0, 0)

    sobj.banner_port = _bannerView.frame;   //CGRect(0, 0, 0, 0)

    sobj.ad_height = 40.0;

    sobj.is_ipad = (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad);    //YES or NO

    sobj.ads_removed = NO;

}