I want to create a program which calculates how long it will take to repeat a process a certain number of times. I've scaled this down a lot for this example.

So, I have some textboxes which are bound to properties in a class:

Count: <TextBox x:Name="txtCount" Text="{Binding Count, Mode=TwoWay}" Width="50"/>
Days: <TextBox x:Name="txtDays" Text="{Binding Days, Mode=TwoWay}" Width="50"/>

and a textblock which is multibound like so:

<TextBlock x:Name="tbkTotal">
    <TextBlock.Text>
        <MultiBinding StringFormat="Days: {0}, Count: {1}">
            <Binding Path="Days" /> /* This isn't updating */
            <Binding Path="Count" />
        </MultiBinding>
    </TextBlock.Text>
</TextBlock>

My DataContext is set in the Window1.xaml.cs file.

public Window1() { InitializeComponent(); Sample sample = new Sample(); this.DataContext = sample; }

I can update the multibound textblock with the Count property just fine, but the Days property always shows 0, even though the Days input accurately reflects changes. I believe that this is because my accessors are different for Days - namely, the Set method. This class is in a different file.

public class Sample : INotifyPropertyChanged { private int _count; private TimeSpan _span;

    public int Count 
    { 
        get { return _count; } 
        set 
        { 
            _count = value;
            NotifyPropertyChanged("Count"); /* Doesn't seem to be needed, actually */
        } 
    }

    public TimeSpan Span { get { return _span; } }

/* The idea is to provide a property for Days, Hours, Minutes, etc. as conveniences to the inputter */

    public double Days
    {
        get { return _span.Days; }
        set
        {
            TimeSpan ts = new TimeSpan();
            double val = value > 0 ? value : 0;
            ts = TimeSpan.FromDays(val);
            _span.Add(ts);
            NotifyPropertyChanged("Span"); /* Here I can only get it to work if I notify that Span has changed - doesn't seem to be aware that the value behind Days has changed. */
        }
    }

    private void NotifyPropertyChanged(string property)
    {
        if (null != this.PropertyChanged)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(property));
        }
    }
    public Sample()
    {
        _count = 0;
        _span = new TimeSpan();
    }
    public event PropertyChangedEventHandler PropertyChanged;
}