How to create a Custom Routed Event ? WPF c#

Question

I followed this tutorial but I couldn't apply what I learned to my project.

I have a LineGraph object (Dynamic Data Display) and I want to create an event that is raised when the thickness of the LineGraph is equal to 0.

How am I supposed to write it following this tutorial ?

Answer 1

Personally, I usually avoid creating events, preferring instead to create delegates. If there is some particular reason that you specifically need an event, then please ignore this answer. The reasons that I prefer to use delegates are that you don't need to create additional EventArgs classes and I can also set my own parameter types.

First, let's create a delegate:

public delegate void TypeOfDelegate(YourDataType dataInstance);

Now a getter and setter:

public TypeOfDelegate DelegateProperty { get; set; }

Now let's create a method that matches the in and out parameters of the delegate:

public void CanBeCalledAnything(YourDataType dataInstance)
{
    // do something with the dataInstance parameter
}

Now we can set this method as one (of many) handlers for this delegate:

DelegateProperty += CanBeCalledAnything;

Finally, let's call our delegate... this is equivalent to raising the event:

if (DelegateProperty != null) DelegateProperty(dataInstanceOfTypeYourDataType);

Note the important check for null. So that's it! If you want more or less parameters, just add or remove them from the delegate declaration and the handling method... simple.

Answer 2

Here is how I would do it with a RoutedEvent:

1. Create a class that derives from LineGraph, let's say CustomLineGraph:

   public class CustomLineGraph : LineGraph {
   }
   

2. Create our routed event like this:

   public class CustomLineGraph : LineGraph {
   
       public static readonly RoutedEvent ThicknessEvent = EventManager.RegisterRoutedEvent("Thickness", RoutingStrategy.Bubble, typeof(RoutedEventHandler, typeof(CustomLineGraph));
   
       // .NET event wrapper
       public event RoutedEventHandler Thickness
       {
           add { AddHandler(CustomLineGraph.ThicknessEvent, value); } 
           remove { RemoveHandler(CustomLineGraph.ThicknessEvent, value); }
       }
   }
   

3. Now we override the StrokeThickness property so we can raise our custom routed event when the value of that property is 0.

   public class CustomLineGraph : LineGraph {
   
       public static readonly RoutedEvent ThicknessEvent = EventManager.RegisterRoutedEvent("Thickness", RoutingStrategy.Bubble, typeof(RoutedEventHandler, typeof(CustomLineGraph));
   
       // .NET event wrapper
       public event RoutedEventHandler Thickness
       {
           add { AddHandler(CustomLineGraph.ThicknessEvent, value); } 
           remove { RemoveHandler(CustomLineGraph.ThicknessEvent, value); }
       }
   
       public override double StrokeThickness {
           get { return base.StrokeThickness; }
           set
           {
               base.StrokeThickness = value;
               if (value == 0)
                   RaiseEvent(new RoutedEventArgs(CustomLineGraph.ThicknessEvent, this));
           }
       }
   }
   

4. We are done !