通过日期字符串("yyyy-MM-dd")获取当前星期

@implementation NSString (GetWeek)
- (NSString *)getWeek {
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    dateFormatter.dateFormat = @"yyyy-MM-dd";
    NSDate *date = [dateFormatter dateFromString:self];
    [dateFormatter release];
    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    NSInteger unitFlags = NSWeekdayCalendarUnit;
    NSDateComponents *comps = [calendar components:unitFlags fromDate:date];
    [calendar release];
    int week = [comps weekday];
    switch (week) {
        case 1:
            return @"星期天";
            break;
        case 2:
            return @"星期一";
            break;
        case 3:
            return @"星期二";
            break;
        case 4:
            return @"星期三";
            break;
        case 5:
            return @"星期四";
            break;
        case 6:
            return @"星期五";
            break;
        case 7:
            return @"星期六";
            break;
        default:
            return @"星期天";
            break;
    }
}