perform background task on different thread in iOS -


how preform operation in background on different thread, if executed on main thread blocking ui of app. 1 have idea how it?

even if prints nslog in background fine. want run following thing in no matter if user presses home button. in viewcontroller did :

- (ibaction)btnstartclicked:(uibutton *)sender {     [nsthread detachnewthreadselector:@selector(startbgtask) totarget:self withobject:nil];      }  -(void)startbgtask{     [[[uiapplication sharedapplication] delegate] performselector:@selector(startthread)];     }

and in appdelegate.m have method 

 -(void) startthread {  @autoreleasepool {     (int = 0; < 100; i++) {         dispatch_async(dispatch_get_global_queue(dispatch_queue_priority_default, 0), ^{             nslog(@"current progress %d", i);         });         [nsthread sleepfortimeinterval:1];     }    }  }

it prints integer 1 100 on interval of 1 second.

add these properties .h file

@property (nonatomic, strong) nstimer *updatetimer; @property (nonatomic) uibackgroundtaskidentifier backgroundtask;

now replace btnstartclicked method this,

-(ibaction)btnstartclicked:(uibutton *)sender {     self.updatetimer = [nstimer scheduledtimerwithtimeinterval:0.5                                                         target:self                                                       selector:@selector(calculatenextnumber)                                                       userinfo:nil                                                        repeats:yes];     self.backgroundtask = [[uiapplication sharedapplication] beginbackgroundtaskwithexpirationhandler:^{         nslog(@"background handler called. not running background tasks anymore.");         [[uiapplication sharedapplication] endbackgroundtask:self.backgroundtask];         self.backgroundtask = uibackgroundtaskinvalid;     }];      }   -(void)calculatenextnumber{     @autoreleasepool {       // executed no matter app in foreground or background     } }

and if need stop use method,

 - (ibaction)btnstopclicked:(uibutton *)sender {      [self.updatetimer invalidate];     self.updatetimer = nil;     if (self.backgroundtask != uibackgroundtaskinvalid)     {         [[uiapplication sharedapplication] endbackgroundtask:self.backgroundtask];         self.backgroundtask = uibackgroundtaskinvalid;     }     = 0; }

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