Get number of instances of custom class

问题

I have created a custom class in xcode: PaperPack and defined 2 instant variables: title and author-

Then I alloc 2 instances of the class as below:

PaperPack *pack1 = [[PaperPack alloc] init];
pack1.title = @"Title 1";
pack1.author = @"Author";

PaperPack *pack2 = [[PaperPack alloc] init];
pack1.title = @"Title 2";
pack1.author = @"Author";

Then how do I count and return number of instances I have created with that class?

回答1:

No you can not get directly. Whenever you create in instance add it any Array and then access it using that array properties.

Ex :

NSMutableArray *allInstancesArray = [NSMutableArray new];
PaperPack *pack1 = [[PaperPack alloc] init];
pack1.title = @"Title 1";
pack1.author = @"Author";
    [allInstancesArray addObject:pack1];

PaperPack *pack2 = [[PaperPack alloc] init];
pack1.title = @"Title 2";
pack1.author = @"Author";
    [allInstancesArray addObject:pack2];

Then get count as :

NSLog(@"TOTAL INSTANCES : %d",[allInstancesArray count]);

回答2:

You could create a factory singleton which you use to count the number of instances requested (then you must create all instances using the factory). Or you could add a static variable into the PaperPack class and increment it each time (in the init method, then you must call init each time).

回答3:

static PaperPack *_paperPack;

@interface PaperPack ()

@property (nonatomic, assign) NSInteger createdCount;

- (PaperPack *)sharedPaperPack;

@end

@implementation PaperPack

+ (PaperPack *)sharedPaperPack
{
    @synchronized(self)
    {       
        if(!_sharedPaperPack)
        {

             _sharedPaperPack = [[[self class] alloc] init];

        }
    }
    return _sharedPaperPack;
}

+ (PaperPack*)paperPack {
    self = [super init];
    if (self) {
        [PaperPack sharedPaperPack].createdCount ++;
    }
    return self;
}

To use it:

Just call class method which will increase "createdCount" value

PaperPack *firstPaperPack = [PaperPack paperPack];
PaperPack *secondPaperPack = [PaperPack paperPack];

and to count:

NSInteger count = [PaperPack sharedPaperPack].createdCount;

Sorry if something is incorrect, code is written from memory

回答4:

You can also do the following Method 1

// PaperPack.h
@interface PaperPack : NSObject
+ (int)count;
@end

// PaperPack.m
static int theCount = 0;

@implementation PaperPack
-(id)init
{
  if([super init])
   {
     count = count + 1 ; 
   }
  return self ;
}
+ (int) count
 { 
   return theCount; 
  }
@end

when you want the number of objects created

[PaperPack count];

Method 2

1)add a property to your class PaperPack.h

@property (nonatomic,assign) NSInteger count ;

2)synthesize it in PaperPack.m

@synthesize count ;

3) modify init method

-(id)init
{
  if([super init])
   {
     self = [super init] ;
     self.count = self.count + 1 ; 
   }
   return self ;
}

4)when you want the number of objects created

  NSLog(@"%d",pack1.count);
   NSLOg(@"%d",pack2.count);

来源：https://stackoverflow.com/questions/17850883/get-number-of-instances-of-custom-class