C＃事件/按下GUI时阻止

Question

I'm working on a custom GUI with SharpDX.

I have user Input from a Form Object and assign Action Methods to the specific events. Below my UI I have a "drawing canvas" and I use Tool Objects that also listen to those Form Events.

But I'm a bit stuck on the matter of how to design my program to only pass those events to a second layer (in this case my canvas) when the first layer did not "hit" anything. In short: Only call "Tool.OnMouseDown" when "Button.OnMouseDown" did return false? Would a Chain Of Responsibility be the/a correct or possible approach?

Or shall I make the current Tool check if "Excecute (Vector2)" is above some gui element but I think this would lead to the kind of coupling I want to prevent.

Hope someone is willing to help/hint (sorry for no code examples, if it's to confusingly descriped please tell me ;))

Thanks!

(Disclaimer: I know I don't have to reinvent the wheel, but I use it partly to learn and improve on my design patterns and coding skills)

---

thanks to sharp-ninja's answer i did the following:

ok working with it like this now :) thanks again Mister Ninja

using System.Windows.Forms;  

public class HandleMouseEventArgs : MouseEventArgs  
{  
    public bool handled { get; protected set; }  

    public HandleMouseEventArgs(MouseEventArgs args) : base(args.Button, args.Clicks, args.X, args.Y, args.Delta)  
    {  
        handled = false;  
    }  

    public void SetHandled()  
    {  
        handled = true;  
    }  
}  

Answer 1

Fortunately in .Net events get called in the order in which they are registered. You can use a handlable event arg so that the first handler of the event can tell subsequent event handlers whether the event was handled.

 event EventHandler<MyHandlableEventArg> MultiLevelEvent;

Then in your main program:

 // First event handler
 MultiLevelEvent += (s, e) => { if(x) e.Handled = true; };

 // Subsequent event handler
 MultiLevelEvent += (s, e) => { if(!e.Handled) { /* Do Work */ } };