Question

Considering you have an MVVM Architecture in WPF like Josh Smith’s examples

How would you implement two properties ‘synced’ that update eachother? I have a Price property, and a PriceVatInclusive property in my model.

-When the Price changes, I want to see the Vat inclusive price to automatically be ‘Price * 1.21’.

-Vice versa, when the PriceVatInclusive changes, I want the Price to be ‘PriceVatInclusive / 1.21’

Any ideas on that?

And what if your model is a Entity framework entiry? You can’t use the approach above then… no? Should you put calculating code in the ViewMOdel or … ?

Answer 1

One way:

    public class Sample : INotifyPropertyChanged     {         private const double Multiplier = 1.21;         #region Fields         private double price;         private double vat;         #endregion          #region Properties         public double Price         {             get { return price; }             set             {                 if (price == value) return;                 price = value;                 OnPropertyChanged(new PropertyChangedEventArgs('Price'));                 Vat = Price * Multiplier;             }         }          public double Vat         {             get { return vat; }             set             {                 if (vat == value) return;                 vat = value;                 OnPropertyChanged(new PropertyChangedEventArgs('Vat'));                 Price = Vat / Multiplier;             }         }         #endregion          #region INotifyPropertyChanged Members         protected void OnPropertyChanged(PropertyChangedEventArgs e)         {             PropertyChangedEventHandler ev = PropertyChanged;             if (ev != null)             {                 ev(this, e);             }         }         public event PropertyChangedEventHandler PropertyChanged;          #endregion     } 

If you can derive from DependencyObject, you can use Dependency Properties.

public class Sample : DependencyObject {     private const double Multiplier = 1.21;      public static readonly DependencyProperty VatProperty =         DependencyProperty.Register('Vat', typeof(double), typeof(Sample),          new PropertyMetadata(VatPropertyChanged));      public static readonly DependencyProperty PriceProperty =         DependencyProperty.Register('Price', typeof(double), typeof(Sample),          new PropertyMetadata(PricePropertyChanged));      private static void VatPropertyChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)     {         Sample sample = obj as Sample;         sample.Price = sample.Vat / Multiplier;     }      private static void PricePropertyChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)     {         Sample sample = obj as Sample;         sample.Vat = sample.Price * Multiplier;     }      #region Properties     public double Price     {         get { return (double)GetValue(PriceProperty); }         set { SetValue(PriceProperty, value); }     }      public double Vat     {         get { return (double)GetValue(VatProperty); }         set { SetValue(VatProperty, value); }     }     #endregion }