使用字符串比较两个时间的大小

- (NSString *)compareStr1:(NSString *)str1 withStr2:(NSString *)str2{

NSString *hour = nil;

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:@"yyyy-MM-dd HH:mm"];

NSDate *date1 = [formatter dateFromString:str1];
NSDate *data2 = [formatter dateFromString:str2];

NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierChinese];
unsigned int usitFlags = NSCalendarUnitMinute;

NSDateComponents *coms = [gregorian components:usitFlags fromDate:date1 toDate:data2 options:0];

NSInteger minute = [coms minute];
NSLog(@"minute- - - - -%ld",(long)minute);

CGFloat hour1 = minute / 60;

NSInteger hour2 = minute % 60;
if (hour2 > 30) {
hour1 = hour1 + 1;
}
else if (hour2 > 0 && hour2 <= 30){
hour1 = hour1 + 0.5;
}
hour = [NSString stringWithFormat:@"%.1f",hour1];

return hour;
}