CLIM mail archive


Re: Problem using Handle-event

  >From: Scott McKay <>
  >For CLIM stream panes, I think you can probably safely wrap an :AROUND
  >method on the CLIM-INTERNALS::RECEIVE-GESTURE method.

  Surely Martin did The Right Thing; i.e. he followed the event protocol as
  outlined by any reasonable reading of the documentation.  But as he
  discovered, this simply doesn't work.  ...

Indeed, I was a little worried about using a function that was not
exported from the CLIM-INTERNALS package to do what I took to be the
job of a function that was exported from the CLIM package.  As Scott
suggested, it did pretty much the right thing, but I seemed to get
four copies of every event instead of no copies of most events.

At this point I went back to the language specifications (I was using
the User Manual), and could not find HANDLE-EVENT documented there.
Indeed, the specification do not say much of anything about events.
On the other hand, the specification did say a lot about streams, and,
it turns out, what I really wanted to do (process the characters typed
at the keyboard separately from I/O from other sources) was well
supported.  There is a function STREAM-READ-CHAR that returns the
characters typed onto the stream.  Using this function on the stream
that has the input focus reads characters and nothing but character.
I did not have to deal with the low level functionality.

One other problem arose though.  We also need to read commands, and
there seemed to be no non-blocking way to do this.  We were back to
the starting point.  The system would need to wait until a command was
read before it could go on processing input from other sources.  There
also turned out to be a simple fix for this problem.  We simply
specialized the READ-FRAME-COMMAND so that it times out after a
second.  The following function is the one we wrote to test this
hypothesis.  In real life, we will want to use READ-COMMAND instead of
ACCEPT, and we will want to process out character I/O in the body of
the default top level rather than in READ-FRAME-COMMAND, but it shows
how the thing worked for us.

(defmethod CLIM:READ-FRAME-COMMAND ((frame graphics-interface) &key stream)
  (MP:with-timeout (1)
    (if (CLIM:stream-peek-char stream)
        (format (CLIM:get-frame-pane CLIM:*application-frame* 'display)
                "<event ~s>~%" (stream-read-char stream))
      (CLIM:accept 'CLIM:command :stream stream))))

We learned two lessons from this experience.  First, if we need to do
something simple (i.e. process the character input separately) there
is usually a high level way to do it.  If we find ourselves wondering
about the low level details, we probably missed something.  Second,
the language specification is a better source of information about the
language than is the user manual.  My only regret regarding this
second lesson is that my copy of the specification has no index.

	Thanks for the suggestions,



Main Index | Thread Index