Cfrgtkky

I want to cache public properties that depend on one or more DependencyProperty values, such that they only get recalculated when the DependencyProperty changes. My class inherits from FrameworkElement and INotifyPropertyChanged. I've followed some portions the answer here Implementing INotifyPropertyChanged. Simplified class:

public class ElementBase : FrameworkElement, INotifyPropertyChanged {

    static ElementBase() {

        WidthProperty.OverrideMetadata(typeof(ElementBase), new FrameworkPropertyMetadata(new PropertyChangedCallback(OnCalculatedValueChanged)));

        HeightProperty.OverrideMetadata(typeof(ElementBase), new FrameworkPropertyMetadata(new PropertyChangedCallback(OnCalculatedValueChanged)));

    }



    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged([CallerMemberName] string propertyName = null) => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));



    private static void OnCalculatedValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) {

        // how can property's string name be avoided

        switch (e.Property.ToString())  { // force update of non-dependency properties 

            case "Height": // is there a better way to force the recalculations?

                ((ElementBase)d).HalfHeight = 0.0; // set overwrites with calculated value 

                ((ElementBase)d).Center = new Point(0, 0);  // set overwrites with calculated value 

                break;

            case "Width": 

                ((ElementBase)d).HalfWidth = 0.0;  // set overwrites with calculated value 

                ((ElementBase)d).Center = new Point(0, 0);  // set overwrites with calculated value  

                break;

            default: break;

        }

    }



    // Caching of the public properties.  

    private double halfWidth; // cached calculated half width

    public double HalfWidth { get => halfWidth; set { halfWidth = Width / 2.0; } }



    private double halfHeight; // cached calculated half height

    public double HalfHeight { get => halfHeight; set { halfHeight = Height / 2.0; } }



    private Point center; // cached calculated center point

    public Point Center { get => center; set { center = new Point(HalfWidth, HalfHeight); } }

}

What I didn't see is:

1. How to attach to PropertyChangedEventHandler events, so related non DependencyProperty properties to be recalculated?


2. How to avoid use of DependencyProperty string names?


3. 
   PropertyChangedCallback entries for OverRideMetadata of the DependencyProperty work, but is that the best way?

I think what you might be looking for is CoerceValue which was intended just for this. Look it up here.