Does an event gets executed twice if callback was assigned twice to the object?

Question

I have a code that attaches an event to a form.

this.form.Resize += new EventHandler(form_Resize);

As you see this is done by +=. If the above code is executed twice or multiple times,

like this:

this.form.Resize += new EventHandler(form_Resize);
this.form.Resize += new EventHandler(form_Resize);
this.form.Resize += new EventHandler(form_Resize);
this.form.Resize += new EventHandler(form_Resize);
this.form.Resize += new EventHandler(form_Resize);

Is the callback method attached multiple times?

How many times will be called the method form_Resize ?

Does an event gets executed multiple times if it's callback method was assigned multiple times to the same object?

Answer 1

The event handler will get called once for each time it is attached. (C#)

To guard against double attachment you can use this pattern:

this.form.Resize -= new EventHandler(form_Resize); 
this.form.Resize += new EventHandler(form_Resize); 

The first statement will not throw an error if there are no handlers attached and will remove an existing handler.