Objective-C Language Singletons Creating Singleton class and also preventing it from having multiple instances using alloc/init.
Example
We can create Singleton class in such a way that developers are forced to used the shared instance (singleton object) instead of creating their own instances.
@implementation MySingletonClass
+ (instancetype)sharedInstance
{
static MySingletonClass *_sharedInstance = nil;
static dispatch_once_t oncePredicate;
dispatch_once(&oncePredicate, ^{
_sharedInstance = [[self alloc] initClass];
});
return _sharedInstance;
}
-(instancetype)initClass
{
self = [super init];
if(self)
{
//Do any additional initialization if required
}
return self;
}
- (instancetype)init
{
@throw [NSException exceptionWithName:@"Not designated initializer"
reason:@"Use [MySingletonClass sharedInstance]"
userInfo:nil];
return nil;
}
@end
/*Following line will throw an exception
with the Reason:"Use [MySingletonClass sharedInstance]"
when tried to alloc/init directly instead of using sharedInstance */
MySingletonClass *mySingletonClass = [[MySingletonClass alloc] init];
