OC's method of acquiring the current time of the system

        
NSDate *date = [NSDate Date];//This is the date of the NSDate type, the year of the year to be obtained is placed here;Nscalendar*cal =[Nscalendar Currentcalendar]; unsignedintUnitflags = nscalendarunityear| nscalendarunitmonth|NscalendarunitDay;//what is the element that you want to get the date from? Get the year will write Nsyearcalendarunit, get the hour to write Nshourcalendarunit, middle with | separate; 
nsdatecomponents*d = [cal Components:unitflags Fromdate:date];//The date element that is to be obtained from date in Unitflags is stored in D of the nsdatecomponents type;//then you can get the specific date from D.
Nsinteger year =[D year];
Nsinteger Month=[D month];
Nsinteger Day=[D Day];
NSLog (@"%ld", year);
NSLog (@"%ld", month);
NSLog (@"%ld", day);

OC's method of acquiring the current time of the system