ios - how can i avoid crash due to preventing variables being @(null)? -

i gettin users location when application executed , if location variables @(null) prevent whit if statement. @ firstviewcontroller.h:

- (void)viewdidload {     [super viewdidload];     // additional setup after loading view.     [super viewdidload];     // additional setup after loading view.     locationmanager = [[cllocationmanager alloc] init];     locationmanager.delegate = self;     locationmanager.desiredaccuracy = kcllocationaccuracyhundredmeters;     [locationmanager startupdatinglocation];  }  cllocationmanager *locationmanager;  - (void)locationmanager:(cllocationmanager *)manager didupdatetolocation:(cllocation *)newlocation fromlocation:(cllocation *)oldlocation {     cllocation *currentlocation = newlocation;     if (currentlocation != null) {         [(appdelegate *)[[uiapplication sharedapplication] delegate] setlatitude:[nsstring stringwithformat:@"%.8f", currentlocation.coordinate.latitude]];          [(appdelegate *)[[uiapplication sharedapplication] delegate] setlongitude:[nsstring stringwithformat:@"%.8f", currentlocation.coordinate.longitude]];     } } 

at secondviewcontroller:

-(void) gettingglobalvariables{     nsstring *userscurrentlatitude = [(appdelegate *)[[uiapplication sharedapplication] delegate] latitude];     nsstring *userscurrentlongitude = [(appdelegate *)[[uiapplication sharedapplication] delegate] longitude];      nsnumberformatter * singsingsing = [[nsnumberformatter alloc] init];     [singsingsing setnumberstyle:nsnumberformatterdecimalstyle];     nsnumber * mynumberlatitude = [singsingsing numberfromstring:userscurrentlatitude];       nsnumberformatter * shecametomeonemorning = [[nsnumberformatter alloc] init];     [shecametomeonemorning setnumberstyle:nsnumberformatterdecimalstyle];     nsnumber * mynumberlongitude = [shecametomeonemorning numberfromstring:userscurrentlongitude];         nslog(@"mynumberlatitude:%@,mynumberlongitude:%@",mynumberlongitude,mynumberlatitude);     if (!mynumberlatitude) {         nslog(@"location variables null");         tabbar *tb =[[tabbar alloc]init];         [tb performselector:@selector(viewdidload)];         [tb performselector:@selector(locationmanager:didupdatetolocation:fromlocation:)];         [self performselector:@selector(gettingglobalvariables)];      } } 

with if statement, when variables null application crush. suggestion?

use this,

    if (currentlocation != [nsnull null] | currentlocation !=nil) {          //write code here.     }