- (NSString*)weekdayStringFromDate:(NSString*)featureDate {
    
    <span style="color:#33cc00;">// 建立 格式 物件</span>
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
   <span style="color:#33cc00;"> // 設定 日期 格式 可以根據自己的需求 隨時調整， 否則計算的結果可能為 nil</span>
    formatter.dateFormat = @"yyyy-MM-dd HH-mm-ss";
    <span style="color:#33cc00;">// 將字串日期 轉換為 NSDate 型別</span>
    NSDate *inputDate = [formatter dateFromString:featureDate];
    <span style="color:#33cc00;">// 生成今天日期時間</span>
    NSTimeInterval secondsPerDay = 24 * 60 * 60;
    NSDate *today = [[NSDate alloc] init];
    NSDate *tomorrow, *yesterday;
    
    tomorrow = [today dateByAddingTimeInterval: secondsPerDay];
    yesterday = [today dateByAddingTimeInterval: -secondsPerDay];
    
    <span style="color:#33cc00;">// 10 first characters of description is the calendar date:</span>
    NSString * todayString = [[today description] substringToIndex:10];
    NSString * yesterdayString = [[yesterday description] substringToIndex:10];
    <span style="color:#33cc00;">//根據返回日期判斷是否是今天還是昨天</span>
    NSString * dateString = [[inputDate description] substringToIndex:10];

    if ([dateString isEqualToString:todayString])
    {
        return @"今天";
    } else if ([dateString isEqualToString:yesterdayString])
    {
        return @"昨天";
    }
   <span style="color:#33cc00;"> //剩下的返回星期幾就行了</span>
    NSArray *weekdays = [NSArray arrayWithObjects: [NSNull null], @"週日", @"週一", @"週二", @"週三", @"週四", @"週五", @"週六", nil];
    
    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    
    NSTimeZone *timeZone = [[NSTimeZone alloc] initWithName:@"Asia/Shanghai"];
    
    [calendar setTimeZone: timeZone];
    
    NSCalendarUnit calendarUnit = NSWeekdayCalendarUnit;
    
    NSDateComponents *theComponents = [calendar components:calendarUnit fromDate:inputDate];
    
    return [weekdays objectAtIndex:theComponents.weekday];
}