iOS日期处理

1、yyyy-MM-dd-> 今天、昨天、MM月dd日，注意dateFormater的格式一定要对应上传参过来的日期格式

+ (NSString *)dateToTitleDateString:(NSString *)dateString {
    NSDateFormatter *dateFormater = [NSDateFormatter new];
    dateFormater.dateFormat = @"yyyy-MM-dd";
    NSDate *today = [NSDate date];
    NSDate *yesterday = [NSDate dateWithTimeIntervalSinceNow:-(24*60*60)];
    NSString *todayString = [dateFormater stringFromDate:today];//今天
    NSString *yestoday = [dateFormater stringFromDate:yesterday];//昨天
    NSString *titleDateString = @"今天";
    if ([dateString isEqualToString:todayString]) {
        titleDateString = @"今天";
    }else if ([dateString isEqualToString:yestoday]){
        titleDateString = @"昨天";
    }else {
        NSDate *tempDate = [dateFormater dateFromString:dateString];
        dateFormater.dateFormat = @"MM月dd日";
        titleDateString = [dateFormater stringFromDate:tempDate];
    }
    return titleDateString;
}