IOS 获取指定月的第一天和最后一天

+ (NSString *)getMonthBeginAndEndWith:(NSString *)dateStr{

NSDateFormatter *format=[[NSDateFormatter alloc] init];
[format setDateFormat:@"yyyy-MM"];
NSDate *newDate=[format dateFromString:dateStr];
double interval = 0;
NSDate *beginDate = nil;
NSDate *endDate = nil;
NSCalendar *calendar = [NSCalendar currentCalendar];

[calendar setFirstWeekday:2];//设定周一为周首日
BOOL ok = [calendar rangeOfUnit:NSMonthCalendarUnit startDate:&beginDate interval:&interval forDate:newDate];
//分别修改为 NSDayCalendarUnit NSWeekCalendarUnit NSYearCalendarUnit
if (ok) {
endDate = [beginDate dateByAddingTimeInterval:interval-1];
}else {
return @"";
}
NSDateFormatter *myDateFormatter = [[NSDateFormatter alloc] init];
[myDateFormatter setDateFormat:@"YYYY.MM.dd"];
NSString *beginString = [myDateFormatter stringFromDate:beginDate];
NSString *endString = [myDateFormatter stringFromDate:endDate];
NSString *s = [NSString stringWithFormat:@"%@-%@",beginString,endString];
return s;
}