获取上个月的日期.m

NSCalendar *calendar = [NSCalendar currentCalendar];
NSDateComponents *dateComponents = [calendar components:NSYearCalendarUnit | NSMonthCalendarUnit fromDate:[[NSDate alloc] init]];
[dateComponents setMonth:dateComponents.month - 1];
NSDate *lastMonthDate = [calendar dateFromComponents:dateComponents];

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
dateFormatter.dateFormat = @"yyyyMM";
lastMonthDateString = [dateFormatter stringFromDate:lastMonthDate];