WPF how to use properties to redraw another element?

Question

So I have a class called signal graph that I want to update when scrollviewer performs a task.

The signal graph is connected to the scrollviewer by these dependency properties:

 public double MinimumXInDIPs
    {
      get { return (double)GetValue(MinimumXInDIPsProperty); }
      set
      {
        SetValue(MinimumXInDIPsProperty, value);
      }
    }
    public static readonly DependencyProperty MinimumXInDIPsProperty =
      DependencyProperty.Register("MinimumXInDIPs",
      typeof(double), typeof(SignalGraph),
      new FrameworkPropertyMetadata(new double()));

    public double ViewportWidth
    {
      get { return (double)GetValue(ViewportWidthProperty); }
      set
      {
        SetValue(ViewportWidthProperty, value);
      }
    }
    public static readonly DependencyProperty ViewportWidthProperty =
      DependencyProperty.Register("ViewportWidth",
      typeof(double), typeof(SignalGraph),
      new FrameworkPropertyMetadata(new double()));


    public int UnitsOfTimePerAxisDivision
    {
      get { return (int)GetValue(UnitsOfTimePerAxisDivisionProperty); }
      set
      {
        SetValue(UnitsOfTimePerAxisDivisionProperty, value);
      }
    }
    public static readonly DependencyProperty UnitsOfTimePerAxisDivisionProperty =
      DependencyProperty.Register("UnitsOfTimePerAxisDivision",
      typeof(int), typeof(SignalGraph),
      new FrameworkPropertyMetadata(1));

However, I don't want to just use a dependency property callback on each of the three properties because all 3 of those properties might change on zoom, which would then result in redrawing the signalgraph way too many times.

Normally I think I would just register all the signalgraphs onto a ZoomEvent, but the signal graphs don't have access to the scrollviewer directly. I figure that in WPF it would be more natural to connect them using properties somehow.

I can just make a property bool NeedsToRedraw on the scrollviewer that I only set to true when the zoom has taken place. Then I can bind the signalgraphs to that property and have a propertychangedcallback that calls the redraw function. However, if i reset the bool to false, it will end up calling the propertychangedcallback one more time even though I don't really need to be calling that function.

will this be inefficient? I feel like in some ways events would be cleaner, since I wouldn't be having the propertychangedcallback first get called when I set the value to true (resulting in a redraw) and then again when I set the value back to false (resulting in no code in the callback, just a useless test)>

I guess it's not a huge deal, but I am just wondering what people would recommend.

Instead I want to update once

Answer 1

Using "NeedsToRedraw" would seemingly work fine, and the superfluous property-changed callback is not likely to cause a performance bottleneck. However, maybe one of these is a better alternative:

1. Since these three properties are connected, make them into a single one, in a wrapper class like ZoomProperties or whatever. (Of course, however, this would also require changes to the consumer class.)
2. Add a timer on the target. Start/reset it when a property changes, and only trigger the handler if a certain delta (maybe 50ms?) elapses.