Binding data calculated from DependencyProperty value

Question

Hi all,

I am attempting to create a custom Templated Control in at UWP app that automatically generates binding data for its child controls based on a provided DependencyProperty specified in the XAML.

For example, imagine I have a Templated Control with the following child controls in the Generic.xaml:

• TextBlock x:Name="ProductName" Text="{TemplateBinding Name}"
• TextBlock x:Name="ProductPrice" Text="{TemplateBinding Price}"
• TextBlock x:Name="DiscountedPrice"

and want to only specify the values for Name and Price in XAML, via

• myControls:Product Name="Potato" Price="5.00"

while having the price after discount automatically calculated via the Product.cs file.

Is it possible to create bindable data for DiscountedPrice based on Price/ProductPrice?

The issue I'm running into is that the properties generated by "propdp" are non-static, and as a result, I am lost on how to make the calculated value bindable by any method. (I'm coming into UWP straight from WinForms...)

// TemplateBinding Price  
public string Price  
{  
   get { return (string)GetValue(PriceProperty); }  
   set { SetValue(PriceProperty, value); }  
}  
public static readonly DependencyProperty PriceProperty =  
DependencyProperty.Register(nameof(Price), typeof(string), typeof(Product), new PropertyMetadata("0.00"));  
  
// Calculated Value of DiscountedPrice  
public string DiscountedPrice => Convert.ToString(Convert.ToInt32(Price) * 0.8);

Answer 1

Hello,​

Welcome to our Microsoft Q&A platform!

You want to dynamically change the value of DiscountedPrice when the Price changes. This is possible.

You can register a callback method for value changes when creating a DependencyProperty, specifically created as follows:

public static readonly DependencyProperty PriceProperty =  
DependencyProperty.Register(nameof(Price), typeof(string), typeof(Product), new PropertyMetadata("0.00",new PropertyChangedCallback(Price_Changed)));  
  
private static void Price_Changed(DependencyObject d, DependencyPropertyChangedEventArgs e)  
{  
    if(e.NewValue!=null && !e.NewValue.Equals(e.OldValue))  
    {  
        double price = Convert.ToDouble(e.NewValue);  
        double discountedPrice = price * 0.8;  
        //Assign values to TextBlock or perform other operations  
    }  
}  

Thanks.

Answer 2

Wow!!

Thank you Richard; that was it!!

I'm not sure if I implemented it properly, but this appears to have gotten the job done:

private static void Price_Changed(DependencyObject d, DependencyPropertyChangedEventArgs e)  
 {  
     if(e.NewValue!=null && !e.NewValue.Equals(e.OldValue))  
     {  
         double price = Convert.ToDouble(e.NewValue);  
         double discountedPrice = price * 0.8;  

         d.SetValue(DiscountedPrice, (string)discountedPrice);  
     }  
 }