Question

I have a calculated property on my View that I need to bind to my ViewModel. I’m using WPF and it seems that there is no way to make a bindable property (Dependency Property) that is self calculating. I don’t want to perform the calculations whenever the View’s state changes because they are time intensive. I want to do the calculations whenever the ViewModel needs the result, i.e. when it closes.

Answer 1

Based on your comment above, I’d use a Converter

Your ViewModel would contain the encrypted data, and the binding to the View uses a Converter which converts it into something readable. When it’s time to save the data back to the ViewModel, use the ConvertBack method of the converter to encrypt the data again.

<TextBox Text="{Binding EncryptedAccountNumber, 
         Converter={StaticResource DecryptTextConverter}}" />

public class DecryptTextConverter: IValueConverter
{
    public object Convert(object value, Type targetType, 
        object parameter, CultureInfo culture)
    {
        // Implement decryption code here
        return decryptedValue;
    }

    public object ConvertBack(object value, Type targetType, 
        object parameter, CultureInfo culture)
    {
        // Implement encryption code here
        return ecryptedValue;
    }
}

If the Encryption code takes a while, set your UpdateSourceTrigger=Explicit and manually trigger the source update when the Save button is clicked.