[3429] in java-interest
Re: TextArea and handleEvent
daemon@ATHENA.MIT.EDU (Gary Aitken)
Sat Nov 11 23:14:00 1995
Date: Sat, 11 Nov 1995 19:28:17 -0700
From: garya@village.org (Gary Aitken)
To: Java Mailing Lists <java@vv.val.net>, java-interest@java.sun.com
> i'm trying to intercept the <enter> key from a textarea object. i have
> tried the following:
>
>class Editor extends TextArea
>{
>public boolean handleEvent( Event evt )
>{
> ... handleEvent code here ....
>}
>}
>
> the problem is that handleEvent never seems to get called. what am i
> doing wrong? is there a better way of doing this?
I think you have hit a bug (or two).
I may be way off base here, but I'll take a shot at it...
Let's assume you instantiate your Editor as object ed in a Frame called main.
This gives you an object tree which looks like:
main (a Frame)
ed (an Editor)
Events are delivered as follows, as nearly as I can figure out:
The native environment delivers the event to the Java library
(I can't track down how since there are no references
to deliverEvent outside of Component.java and Container.java
in the source distributed with Beta). Eventually,
xxx.deliverEvent
should get called to process the event, where xxx is the object
with the input focus (ed in this case)
The event delivery mechanism has three components:
deliverEvent
Routes the event to the appropriate interior object.
This should be the innermost object for the event coordinates
where the event occurred. For pointer events, it should be the
object under the pointer (in most cases). For Keyboard events,
it should be the object with the keyboard focus.
postEvent
Routes the event to the native toolkit object for processing,
or to the java object for processing. If the java object
decides not to handle the event, propagates it up to the
parent object. The native toolkit part of this is bug#2 below.
handleEvent
Processes the event (possibly)
The overrides of these three functions are as follows:
Component deliverEvent postEvent handleEvent
Container deliverEvent -- --
Window -- -- --
Frame -- -- --
Component deliverEvent postEvent handleEvent
TextComponent -- -- --
TextArea -- -- --
Editor -- -- handleEvent
What *should* happen (I think) is the following,
assuming you have clicked on ed to get the input focus there:
The event gets delivered to ed's Component.deliverEvent
bug #1:
This does not happen on Win95 (I don't think -- justification
for this appears below after bug #2 where we override
postEvent);
I don't know what happens on a unix machine running Motif;
I don't have one handy to test with.
ed's Component.deliverEvent simply calls postEvent which
is ed's Component.postEvent.
Component.postEvent checks to see if a peer object exists
(a peer object is a native window system object)
If one does, it delivers the event to it.
If a peer did not exist, or the peer did not process the event,
postEvent calls handleEvent.
bug #2:
The call to peer.handleEvent prevents your override of
handleEvent from getting called, as the peer object will
process the event (the peer is a text object which does
something with most key events).
The check for the peer and the call to peer.handleEvent
should appear at the top of Component.handleEvent instead of
in Component.postEvent
In order to get around the above bug #2, you *should* be able to
override postEvent. However, doing so does not correct the problem,
indicating that bug #1 exists. If you are on a unix system you
might try this, just in case it solves the problem there. I don't
think it will, however.
Unfortunately, this does not solve your problem, but it does, I hope,
provide some additional information which may help find it.
If, instead of deriving from a text object, you derive from something
like a Panel, which has a peer object which does not consume key events,
you will see that your override of handleEvent works,
an indication that there is a bug in the event delivery mechanism,
or at least that it does not have uniform behavior.
Gary Aitken garya@village.org
-
This message was sent to the java-interest mailing list
Info: send 'help' to java-interest-request@java.sun.com
