Question

How to convert this property to a dependency property ? Regarding that everybody just said that “Do not use logic in dependency property” and didn’t proposed a remedy for that :

    public DateTime? SelectedDateGeorgian
    {
        get
        {
           //choose a control based on this "user control" current mode 
           //and return its value
        }


        set
        {
           //choose a control based on this "user control" current mode 
           // and set its property after some manipulations on the value 
        }
    }

I want to convert it to this :

    public static readonly DependencyProperty SelectedDateGeorgianProperty =
    DependencyProperty.Register("SelectedDateGeorgian", typeof(DateTime?), typeof(MyDatePicker), new PropertyMetadata(default(DateTime?)));

    public DateTime? SelectedDateGeorgian
    {
        get
        {
            //Its prohobited to do something here ! So what should I do ?
            //How should I select a control and return its value here ?
            //I can't have a simple backing variable because I should do some conversion here                 

            return (DateTime?)GetValue(SelectedDateGeorgianProperty);
        }
        set
        {
             //I want to convert received value here and 
             // and after that update some UI properties in this user control

            SetValue(SelectedDateMiladiProperty, value);
        }
    }

I want to convert the value which is going to be written in this dependency property and also update UIElements.

And also I want to convert a value from an UIElement and return the converted value whenever it’s going to be read.

So you see that I can’t have a simple backing variable.

Please somebody give me a pattern to implement this.

Thanks for your attention.

Answer 1

Yes, you can.

You have to bind your UIElement property to this DependencyProperty and use a Converter. See How to: Convert Bound Data.

BTW: Here you can find the reason, why DependencyProperties shouldn’t have additional logic in the property wrapper.

Edit:

<DatePicker Name="dp1"
            SelectedDate="{Binding Path=SelectedDateGeorgian,
                                   RelativeSource="{RelativeSource AncestorType=UserControl}"}" />
<DatePicker Name="dp2"
            SelectedDate="{Binding Path=SelectedDateGeorgian,
                                   RelativeSource="{RelativeSource AncestorType=UserControl}",
                                   Converter={StaticResource dateConverter}}" />

create the converter:

[ValueConversion(typeof(DateTime?), typeof(DateTime?))]
public class DateConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        // your conversions
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        // your backconversions
    }
}

and add it as a resource:

<src:DateConverter x:Key="dateConverter"/>