iphone - Thread and NSTimer -

i making application has timer. count minutes , seconds given time down 0. when happen launch alertview.

my structure this:

mainthread method allocate new thread , initialize it. entrypoint(method) thread has timer invokes method calculating time left, , if time up, displays alertview.

however, correct? because updating gui thread main...and bad right? , displaying alertview thread.

i thought of making method encapsulate logic updating , displaying alertview , in method nstimer invokes use performselectorinmainthread, correct?

thanks time.

assuming it's simple determine how time left, run timer on main thread. timer gets attached current runloop, it's not blocking anywhere, , callback method shouldn't take inordinate amount of time run, , can therefore update ui nicely.

- (void) initializetimerwithendtime: (nsdate *) endtime {     // call on main thread & it'll automatically     // install timer on main runloop     self.countdowntimer = [nstimer scheduledtimerwithtimeinterval: 1.0                                                            target: self                                                          selector: @selector(timertick:)                                                          userinfo: endtime                                                           repeats: yes]; #if __target_os_iphone__     // fire while tracking touches     [[nsrunloop mainrunloop] addtimer: self.countdowntimer                               formode: uitrackingrunloopmode]; #else     // fire while tracking mouse events     [[nsrunloop mainrunloop] addtimer: self.countdowntimer                               formode: nseventtrackingrunloopmode];     // fire while showing application-modal panels/alerts     [[nsrunloop mainrunloop] addtimer: self.countdowntimer                               formode: nsmodalpanelrunloopmode]; #endif }  - (void) cancelcountdown {     [self.countdowntimer invalidate];     self.countdowntimer = nil; }  - (void) timertick: (nstimer *) atimer {     nsdate * enddate = [timer userinfo];     nsdate * = [nsdate date];      // have passed end date?     if ( [enddate laterdate: now] == )     {         // show alert         [self cancelcountdown];         return;     }      // otherwise, compute units & show     nsuinteger units = nshourcalendarunit|nsminutecalendarunit|nssecondcalendarunit;      nsdatecomponents * comps = [[nscalendar currentcalendar] components: units                                                                fromdate: [nsdate date]                                                                  todate: enddate                                                                 options: 0];     [self.clockview sethours: comps.hour                      minutes: comps.minute                      seconds: comps.second]; }