objective c - How to invalidate contents of UIView to force a redraw? -

i have uiview acts schedule (ipad app written using xcode 4.6, ios 6.2 , storyboards). have 2 (2) uiviews, 1 in top half of window, other in bottom half. there calendar in top half; , grid of times below that. when user taps on day has appointments, drawn on bottom uiview. user can tap day appointments, , old removed, new data drawn on bottom view.

this works great, unless there no appointments day tapped, in case old data remains, rather being somehow deleted. have tried [self setneedsdisplay], since nothing has changed, nothing drawn. there way invalidate contents of uiview force redrawn no data?

update: here code draws appointments:

- (void)drawrect:(cgrect)rect  {  //  load dictionary files plists nsstring *path = [[nsbundle mainbundle] bundlepath]; //    nslog(@"\n\npath %@",path); // nsstring *timesfinalpath = [path stringbyappendingpathcomponent:@"startingtimes.plist"];  //  starting times nsdictionary *startdict = [nsdictionary dictionarywithcontentsoffile:timesfinalpath];  nsstring *namesfinalpath = [path stringbyappendingpathcomponent:@"technames.plist"];  //  tech names nsdictionary *techdict = [nsdictionary dictionarywithcontentsoffile:namesfinalpath]; //    nslog(@"\npath: %@\ntechdict.count: %d\nstartdict.count %d", path, techdict.count, startdict.count);  //    nslog(@"nbr of recognizers: %lu", (unsigned long)self.gesturerecognizers.count);   //  find out how many appointments have day singletonappointments *sharedinstance = [singletonappointments sharedinstance];  //  initialize  if(sharedinstance.globalapptlist.count > 0) {      for(int = 0; < sharedinstance.globalapptlist.count; i++)  {  //  customer apointments day          appointmentinfo *apptobject = [sharedinstance.globalapptlist objectatindex:i];          //nslog(@"apptobject.aapptkey: %@", apptobject.aapptkey);          //  using apptobject.aapptkey, client's name         nspredicate *predicate =  ([nspredicate predicatewithformat:@"(aclientkey = %@)", apptobject.aapptkey]);         clientinfo = [clientinfo mr_findallwithpredicate: predicate];         nsstring *cliinfo;         (clientinfo *cli in clientinfo) {             cliinfo = cli.aclientname;  //  found client name         }          //  settings name drawing         const float namefontsize = 14;         uifont *hourfont=[uifont systemfontofsize: namefontsize];          //  compute duration         nsdateformatter *df = [[nsdateformatter alloc] init];         [df setdateformat:@"hh:mm"];         nstimeinterval interval = [apptobject.aendtime timeintervalsincedate:apptobject.astarttime];         int hours = (int)interval / 3600;             // integer division hours part         int minutes = (interval - (hours*3600)) / 60; // interval minus hours part (in seconds) divided 60 yields minutes         //            nsstring *duration = [nsstring stringwithformat:@"%d:%02d", hours, minutes];          //  localize time         nsdate *stime = [self localizedate: apptobject.astarttime];         //            nsdate *etime = [self localizedate: apptobject.aendtime];         //            nslog(@"\n\nstime: %@    etime: %@", stime, etime);         //            nslog(@"\nlocalized stime: %@\nlocalized etime %@", stime, etime);          //  determine time slot  (dictiionary starts @ 0900... must accomodate that)         nsdateformatter *formatter = [[nsdateformatter alloc] init];         [formatter settimezone:[nstimezone timezonewithname:@"gmt"]];  //optionally time zone converstions         [formatter setdateformat:@"hh:mm"];          //  time shop opens , closes         preferencedata *prefdatafound = [preferencedata mr_findfirst];         if(prefdatafound)  {  //  fill times             starthour = prefdatafound.ashopopens;             endhour = prefdatafound.ashopcloses;         }         //            nslog(@"starthour: %@    endhour: %@",starthour, endhour);          //  now, first time slot in dictionary         nsarray *ts = [startdict allkeysforobject:[nsnumber numberwithint:5]];  //  comes 1 entry: 9:00          //  clean (remove colon)         nsstring *dictvalue = ts[0];         nsstring *cleandictvalue = [dictvalue stringbyreplacingoccurrencesofstring:@":" withstring:@""];          //  convert int         int dictstarttime = [cleandictvalue intvalue];         int intstarthour = [starthour intvalue];          //  compute gridtimeoffset         float gridtimeoffset = dictstarttime - intstarthour;          nsstring *stringfromdate = [formatter stringfromdate:stime];         //            nslog(@"\n\nstringfromdate: %@",stringfromdate);         //            nslog(@"\nservicetech: %@", apptobject.aservicetech);          //  find correct column tech name         nsnumber *techcolumn = [techdict objectforkey:apptobject.aservicetech];         //            nslog(@"\nservicetech: %@, techcolumn: %@", apptobject.aservicetech, techcolumn);          //  set context         cgcontextref context = uigraphicsgetcurrentcontext();           //  draw name...  (x refers column; y refers time slot)         [[uicolor bluecolor] set];  //  sets color of customer name         nsnumber *timeslot = [startdict objectforkey:stringfromdate];         float correctedslot = [timeslot floatvalue] + gridtimeoffset;  //  corrected slot info name , rectangle         [cliinfo drawatpoint:cgpointmake([techcolumn floatvalue], correctedslot) withfont:hourfont];         //            nslog(@"\ntimeslot: %@    adjusted: %@", [timeslot floatvalue], ([timeslot floatvalue] - gridtimeoffset));           //  make settings blocking         uigraphicsbeginimagecontext(self.bounds.size);         //            cgcontextsetstrokecolorwithcolor(context, [uicolor blackcolor].cgcolor);         //            cgcontextsetlinewidth(context, 1.0);          //  cgcontextref drawing rectangle         cgcontextsetfillcolorwithcolor(context, [[[uicolor graycolor] colorwithalphacomponent: 0.3] cgcolor]);          //            nsnumber *startpos = [startdict objectforkey:stringfromdate];         int shadeheight = ((hours * 4) + (minutes / 15)) * 25;  //  compute starting y value          //            cgcontextfillrect(context, cgrectmake([techcolumn floatvalue], [startpos floatvalue], 218, (float)shadeheight));         cgcontextfillrect(context, cgrectmake([techcolumn floatvalue], correctedslot, 218, (float)shadeheight));          uigraphicsendimagecontext();  //  end context other appointments draw     }  } 

}

this should handled in callback of view controller of controls bottom view. (if have 1 view controller controls both top , bottom, same applies.) in update method (which should called when day selected, including empty days) there should this.

-(void)update {     if (selectedday.events && selectedday.events.count) {        // normal update     }     else {        // empty view     } } 

note if bottom view or has table view, reset data array or set (above referenced selectedday.events) , call

[_tableview reloaddata];  

if have other scheme have empty "manually".

edit

as spokane-dud pointed out, there flaw data source singleton. data has explicitly set nothing when appropriate.

if(appointmentinfo.count > 0) {      (appointmentinfo *appt in appointmentinfo) {        sharedinstance.globalapptlist = appointmentinfo; // move data sharedinstance      }  }  else {      sharedinstance.globalapptlist = nil;  }