UiKit should be called from the main thread only warning - ios

Question

I am adding an event to a calendar on the click of a button. Whenever I click on that button the Xcode gives me a warning and hangs the app for about few seconds and then add the event into the calendar. the warning is as follows:
void _WebThreadLockFromAnyThread(bool), 0x175bd5c0: Obtaining the web lock from a thread other than the main thread or the web thread. UIKit should not be called from a secondary thread.
the code which I am using for adding the event is as follows:
- (IBAction)btn_reminder_click:(id)sender{
[self addEventTocalendar];
}
- (void)addEventTocalendar{
EKEventStore *store = [[EKEventStore alloc] init];
[store requestAccessToEntityType:EKEntityTypeEvent completion:^(BOOL granted, NSError *error) {
if (!granted) { return; }
EKEvent *event = [EKEvent eventWithEventStore:store];
if (btn_appointment.isSelected) {
event.title = #"Appointment Reminder.";
}
else if (btn_pickup.isSelected){
event.title = #"Pickup Reminder";
}
event.startDate = self.selectedDate;
event.endDate = [event.startDate dateByAddingTimeInterval:60*60];//set 1 hour meeting
event.notes = txt_notes.text;
event.recurrenceRules = EKRecurrenceFrequencyDaily;
[event addAlarm:[EKAlarm alarmWithRelativeOffset:60.0f * -5.0f]];
if (selectedIndex == 1) {
[event addRecurrenceRule:[[EKRecurrenceRule alloc]initRecurrenceWithFrequency:EKRecurrenceFrequencyDaily interval:1 end:Nil]];
}
else if (selectedIndex == 2){
[event addRecurrenceRule:[[EKRecurrenceRule alloc]initRecurrenceWithFrequency:EKRecurrenceFrequencyWeekly interval:1 end:Nil]];
}
else if (selectedIndex == 3){
[event addRecurrenceRule:[[EKRecurrenceRule alloc]initRecurrenceWithFrequency:EKRecurrenceFrequencyMonthly interval:1 end:Nil]];
}
else if (selectedIndex == 4){
[event addRecurrenceRule:[[EKRecurrenceRule alloc]initRecurrenceWithFrequency:EKRecurrenceFrequencyYearly interval:1 end:Nil]];
}
[event setCalendar:[store defaultCalendarForNewEvents]];
NSError *err = nil;
[store saveEvent:event span:EKSpanThisEvent commit:YES error:&err];
NSString *savedEventId = event.eventIdentifier; //this is so you can access this event later
BOOL isSuceess=[store saveEvent:event span:EKSpanThisEvent error:&err];
if(isSuceess){
UIAlertView *alertview = [[UIAlertView alloc] initWithTitle:#"Event" message:#"Event added in calendar" delegate:self cancelButtonTitle:#"OK" otherButtonTitles:nil];
[alertview show];
}
else{
UIAlertView *alertview = [[UIAlertView alloc] initWithTitle:#"Event" message:[err description] delegate:self cancelButtonTitle:#"OK" otherButtonTitles:nil];
[alertview show];
}
}];
}
cam Somebody help me o this as I am not able to solve this problem.

Answer 1

Your UIAlertView needs to be shown on the main thread. Try this:
if(isSuceess){
UIAlertView *alertview = [[UIAlertView alloc] initWithTitle:#"Event" message:#"Event added in calendar" delegate:self cancelButtonTitle:#"OK" otherButtonTitles:nil];
dispatch_async(dispatch_get_main_queue(), ^{
[alertview show];
});
}
else {
UIAlertView *alertview = [[UIAlertView alloc] initWithTitle:#"Event" message:[err description] delegate:self cancelButtonTitle:#"OK" otherButtonTitles:nil];
dispatch_async(dispatch_get_main_queue(), ^{
[alertview show];
});
}

Answer 2

UI Code must always run on the main thread.
You need to dispatch your code to the main thread. You can use something like this:
Swift
DispatchQueue.main.async
{
// Your code to execute
}