WPF display a string array in a list of objects in XAML

The problem is that you are binding the Text property of your TextBlock to a string[] instead of a string.

What happens internally is that WPF calls the ToString() method on the DaysOfWeek string array, which results in "System.String[]".

What you want is to bind to string.Join("|", DaysOfWeek }).

There are various ways to do this. A highly recommended way would be to create a "view model" that holds the data you actually want to display rather than the data that, say, came out of a database or some other kind of model.

So, you could create a TimeStampViewModel, which looks like this:

public class TimeStampViewModel
{
    public int Id { get; set; }
    public string DaysOfWeek { get; set; }
    public string HoursOfDay { get; set; }

    public TimeStampViewModel(int id, string[] daysOfWeek, string[] hoursOfDay)
    {
        Id = id;
        DaysOfWeek = string.Join("|", daysOfWeek);
        HoursOfDay = string.Join("|", hoursOfDay);
    }
}

Then, instead of binding to TimeStamp objects, you bind to TimeStampViewModel objects, which you create in your code behind class, like so:

TimeStampViewModels = timeStamps
    .Select(x => new TimeStampViewModel(x.Id, x.DaysOfWeek, x.HoursOfDay))
    .ToList();

This assumes you have a property public List<TimeStampViewModel> TimeStampViewModels { get; set; } in your code-behind.

If you want to understand more about view models in general, I recommend you read up on the Model-View-ViewModel (MVVM) pattern. Here as an article published by Microsoft to get you started. MVVM is considered by many to be a best practice for programming in WPF (and other XAML-based frameworks).

To handle your "extra credit" question regarding the strikethrough, that's going to be a bit more tricky. You would need to modify your view model to something like this:

public class TimeStampViewModel
{
    public int Id { get; set; }
    public List<OptionalDayOfWeek> DaysOfWeek { get; set; }
    public string HoursOfDay { get; set; }

    public TimeStampViewModel(int id, string[] daysOfWeek, string[] hoursOfDay)
    {

        Id = id;
        DaysOfWeek = 
            new[] { "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" }
            .GroupJoin(daysOfWeek, day => day, dayOfWeek => dayOfWeek, (day, matches) => new OptionalDayOfWeek { DayOfWeek = day, IsAvailable = matches.Any() })
            .ToList();
        HoursOfDay = string.Join("|", hoursOfDay);
    }
}

public class OptionalDayOfWeek
{
    public string DayOfWeek { get; set; }
    public bool IsAvailable { get; set; }
}

Meanwhile, your XAML would need to present the days of week inside something like an ItemsControl, where each item is bound to a OptionalDayOfWeek. Then you could use an IValueConverter to determine whether the TextDecorations should include a Strikethrough or not. (Sorry, I don't have time to write this part at the moment, but hopefully that's enough of a hint to get started.)

You want to display DaysOfWeek as a text in a TextBlock. DaysOfWeek is a string array not a string so it will be not shown as you expected. You have to convert to a string and you can specify the format in the conversion function. You have to ways to convert your string array to a formatted string in WPF

First solution: The nicer but complex way

public class WeekDaysFormatConverter : System.Windows.Data.IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if(value != null && value is string[])
        {
            return string.Join("|", value as string[]);
        }

        return value;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

And apply it:

<Window.Resources>
    <local:WeekDaysFormatConverter x:Key="WeekDaysFormatConverter" />
</Window.Resources>
...
<TextBlock Text="{Binding DaysOfWeek Converter={StaticResource WeekDaysFormatConverter}}"/>

Second solution: simply use a property to specify the format:

public class TimeStamp
{
    public int ID { get; set; }
    public string[] DaysOfWeek { get; set; }
    public string[] HoursOfDay { get; set; }

 public string DaysOfWeekFormatted
    {
        get
        {
            return DaysOfWeek != null ? string.Join("|", DaysOfWeek) : string.Empty;
        }
    }
}

And apply it:

<TextBlock Text="{Binding DaysOfWeekFormatted}"/>

You can modify the class as like the following:

public class TimeStamp
    {
        private string _HourList;
        private string _DayList;
        private string[] _DaysOfWeek;
        private string[] _HoursOfDay;
        public string[] HoursOfDay
        {
            get { return _HoursOfDay; }
            set
            {
                _HoursOfDay = value;
                _HourList = String.Join("|", value);
            }
        }
        public int ID { get; set; }
        public string[] DaysOfWeek
        {
            get { return _DaysOfWeek; }
            set
            {
                _DaysOfWeek = value;
                _DayList = String.Join("|", value);
            }
        }
        public string DayLis
        {
            get { return _DayList; }
        }
        public string HourList
        {
            get { return _HourList; }
        }
    }

The advantages of defining the class like this:

whenever you assign value to string array DaysOfWeek it will automatically creates a string DayList in that all array elements ware combined together with a delimiter |, Since DayList is a read only property you cannot assign value to it. you will get the value from this property as well at the time of binding

hence your xamal markups will be like the following:

 <StackPanel Orientation="Vertical" VerticalAlignment="Center">
      <TextBlock Text="{Binding ID}"/>
      <TextBlock Text="{Binding DayLis}"/>
 </StackPanel>