NSString *string1;

@property(nonatomic,retain) NSString *string1;

@synthesize string1;

string1=@"Hello Every One";

NSString *string2;

@property(nonatomic,retain)NSString *string2;

@synthesize string2;

[vc1 setString1:[vc2 string2]];

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(aChangeStringMethod:) name:@"anyStringJustMakeItUnique" object:nil];

-(void)aChangeStringMethod:(NSNotification)notification{
     string1 = [((ViewController2 *)[notification object]) string2];
}

[[NSNotificationCenter defaultCenter] postNotificationName:@"anyStringJustMakeItUnique" withObject:self];

[[NSNotificationCenter defaultCenter] postNotificationName:@"anyStringJustMakeItUnique" withObject:vc2];

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(launchTheOtherNotificationMethod:) name:@"anotherNotificationName" object:nil];

-(void)launchTheOtherNotificationMethod:(NSNotification)notification{
     [[NSNotificationCenter defaultCenter] postNotificationName:@"anyStringJustMakeItUnique" withObject:self];
}

[[NSNotificationCenter defaultCenter] postNotificationName:@"anotherNotificationName" withObject:nil];

string1 = [myVC2 string2];

[vc1 setString1:[[vc1 myVC2] string2]];

[[vc2 myVC1] setString1:[vc2 string2]];

[[self parentViewController] setString1:string2]