ios - Best way present and hide UIView on top of UIWindow from NSObject? -

i've nsobject class handle locations , in specific point shows uiview , updates view , hides , vice versa.

i tried few methods addsubview:

[uiapplication sharedapplication].keywindow [uiapplication sharedapplication].windows.firstobject 

i've uilabel on top of uiview updates value (distance point point), somehow doesn't updates view anymore, shows once , thats , doesn't hides back.

my code:

// updates uiview nsobject class: nsmutabledictionary *params = [[nsmutabledictionary alloc] init];             params[@"distance"] = @(distancetotrap);             params[@"traptype"] = @(trap.gettraptype);             params[@"trapid"] = @(trap.gettrapid);              trapalarmactivity = [[trapalarm alloc] initwithuserinfo:params];             [trapalarmactivity setneedsdisplay];             [trapalarmactivity.screenview setneedsdisplay];              [[uiapplication sharedapplication].keywindow addsubview:trapalarmactivity];             [[uiapplication sharedapplication].keywindow setneedsdisplay];  // function inside uiview updates uilabel , somehow doesn't updates anymore - (void)broadcastlocationchange:(nsnotification*)notification {     if (![db istrapalarmopen]) { return; }      dispatch_async(dispatch_get_main_queue(), ^{         if (globaltrap == nil) {             //globaltrap = [db gettrap_trapid:trapid];             globaltrap = [dbat gettrap_trapid:trapid];         }           int distancetotrap = [db gettrapdistance:globaltrap.gettrapid];          if (distancetotrap == 0) {             cllocation *originallocation = kservice_context.locationmanager.location;             cllocation *traplocation = [[cllocation alloc] initwithlatitude:globaltrap.lat longitude:globaltrap.lon];              distancetotrap = [traplocation distancefromlocation:originallocation];         }          nslog(@"trap alarm - trap distance car: %i", distancetotrap);          if (stillnotyetkey)         {             [self changemessageboxwithdistance:distancetotrap];              if (distancetotrap < kfinish_alarm_distance)                 stillnotyetkey = no;             else             {                 if (distancetotrap > lastdistancetotrap) {                     [self finishtrapalarm];                 }                 else {                     [self changemessageboxwithdistance:distancetotrap];                 }             }         }         // check if user exit polygon before passing trap         if (distancetotrap > lastdistancetotrap)         {             distancegrow++;             if (distancegrow >= kcounter_for_close_window_when_distance_grow_user_out) {                 [self finishtrapalarm];             }         }         lastdistancetotrap = distancetotrap;         [self setneedsdisplay];         [[uiapplication sharedapplication].keywindow setneedsdisplay];     }); }  // function removes uiview - (void)dismiss {     [self removefromsuperview];     [[uiapplication sharedapplication].keywindow setneedslayout]; } 

i'm doing wrong in here?

in case want present , dismiss view use presentviewcontroller , dismissviewcontroller same. changing keywindow not advised.