Dumping events

I'm often surprised (or is it dismayed) when questions pop up in news groups surrounding things like event orders for winforms or webforms applications... this isn't rocket science... we're given all the tools to make this easy to figure out!

Lets do a winforms 2.0 app as an example... first off, the earliest point at which can easily get involved is the constructor...  lets have a look:


So I'm going to attach to all the events before the forms components are initialized... now lets have a look at the "AttachToAllEvents" method.


Only magic there is we're using a class called "EventHandlerWrapper" - what's that... well, it's used to create a strongly typed delegate for attaching to an event.

The reason we need this at all is because EventInfo.AddEventHandler(...) is fussy about the kind of delegate you supply, so if you pass in an "EventHandler" for a "CancelEventHandler" event, it'll throw an exception complaining about it's inability to cast between them... there might be an easier way to do this, but I haven't come across it so far.


With a little brain power I'm sure I could've done this without the separate wrapper class, but this is probably a little easier to read at any rate.

Results..?

So.. onto the results - once we run the code and see exactly what order events are happening in, we can then make a pretty table that may not render in most browsers because I cut 'n pasted it from Excel 2007 ;o)

EventName	IsVisible	IsHandleCreated	HasChildren	IsDisposed
Resize	False	False	False	False
SizeChanged	False	False	False	False
ClientSizeChanged	False	False	False	False
ClientSizeChanged	False	False	False	False
ControlAdded	False	False	True	False
ControlAdded	False	False	True	False
StyleChanged	False	False	True	False
TextChanged	False	False	True	False
Move	False	True	True	False
LocationChanged	False	True	True	False
HandleCreated	False	True	True	False
Invalidated	False	True	True	False
StyleChanged	False	True	True	False
ChangeUICues	True	True	True	False
Invalidated	True	True	True	False
BindingContextChanged	True	True	True	False
Load	True	True	True	False
Layout	True	True	True	False
VisibleChanged	True	True	True	False
Activated	True	True	True	False
Shown	True	True	True	False
Paint	True	True	True	False
Paint	True	True	True	False
Paint	True	True	True	False
MouseCaptureChanged	True	True	True	False
Closing	True	True	True	False
FormClosing	True	True	True	False
Closed	True	True	True	False
FormClosed	True	True	True	False
Deactivate	True	True	True	False
HandleDestroyed	True	True	True	False
Disposed	False	False	False	False

The main thing to keep in mind when doing something like this is to avoid making assumptions - we may not be the first or last to attach to the events (depending on the complexity of the form) - and events can trigger other events... which could explain the ordering of some of this data i.e. changes in visibility and handle creation... if anything we are viewing the order of consequences, as opposed to the true order in which the events are invoked (to get that we'd need to override all the OnXXXX methods of the form class... which would be a good job for dynamic proxy :)