Is passing an EventArg around event handlers potentially dangerous?

Question

I'm calling an event handler from another one:

private void launchApplicationToolStripMenuItem_Click(object sender, EventArgs e) {
            listApplications_DoubleClick(listApplications, null); 
        }

        private void listApplications_DoubleClick(object sender, EventArgs e) {

"listApplications" is a ListView.

I had to pass listApplications because I cast sender in the DoubleClick() event to a ListView.

What about the second arg, though? Should I pass null, as shown above, or should I pass "e" like so:

listApplications_DoubleClick(listApplications, e);

Both ways work fine/identically under good circumstances. I don't know if that would be the case if there were an exception, though...

Answer 1

Well, I wouldn´t exactly say dangerous, but it can cause some problems, such as exceptions if not properly handled. In your example, one event is a click event and the other is a double click event, that implies that both the EventArgs object, e, are in fact a MouseEventArgs. Which is good, cause then you don´t have to worry about the second event handler accessing inexistent members of e.

Now let´s suppose you want to call the paint event whenever the user clicks on a button, for instance. In that case the click event then will call the paint event. Now the problem is: the paint event expects a PaintEventArgs, so passing a MouseEventArgs could cause an exception. Of course, if you´re in control of both pieces of code then you can check for yourself to see if there will be any access to a PaintEventArgs specific member. If not, then you´re fine, although I do not see the point of passing the args anyways in this scenario.

Hope that wasn´t too confusing.

Answer 2

No, passing EventArg is not dangerous until unless you are not using ein method listApplications_DoubleClick(object sender, EventArgs e) body.. it is fine to send null,

Answer 3

When you are calling an event handler of an identical event (i.e. when you are calling a doubleclick event from another doubleclick event) you should pass event arguments through to it. Event arguments contain important information about the doubleclick, for example, its location. If the handler "down the chain" does not care about these arguments, passing null will not cause a problem; however, you should not assume that the handler you are calling ignores the argument, and pass something valid to it.

Here is an example of how you can use event arguments to figure out the position of the doubleclick.