<AWT Dev> Proposal for consolidation of KeyboardFocusManagerPeer

[Oleg Sukhodolsky]

On Tue, Nov 15, 2011 at 3:23 PM, Roman Kennke <roman at kennke.org> wrote:
> Hi Anton,
>
>> > On Tue, Nov 15, 2011 at 1:44 PM, Roman Kennke<roman at kennke.org>  wrote:
>> >> Find attached a patch that illustrates the idea (couldn't find a recent
>> >> version of webrev tool online, at least not in
>> >> http://openjdk.java.net/guide/codeReview.html/webrevHelp.html).
>> >>
>> >> It basically moves identical/equivalent code from the peers to java.awt
>> >> package. Notice that this is not yet complete, with this change, the
>> >> methods shouldNativelyFocusHeavyweight() and
>> >> processSynchronousLightweightTransfer() can be removed from the
>> >> KeyboardFocusManagerAccessor and KeyboardFocusManagerPeerImpl classes.
>> >>
>> >> Maybe I am missing something important, i.e. why this code has to be in
>> >> the peers and needs to jump through hoops to satisfy the KFM. ?
>> > I think this is due to the fact that [WX]ComponentPeer are not the
>> > only implementation of ComponentPeer interface,
>> > we also have NullComponentPeer (or something like that) for
>> > lightweight components.
>> > and the code you are moving should be called for heavyweight components only.
>> >
>> > Oleg.
>>
>> Oleg,
>>
>> The requestFocus method is called on the peer of a hw container of the component (which is either
>> the component itself, or the nearest hw parent, as you know).
>> So, I actually have no reason why Roman can't change it like the way he did... Roman split the peer
>> method quite correctly, leaving the peer part to the peer.
>> Don't you agree?
>
> It is probably a little more subtle: The current code doesn't call back
> to the KFM at all for LW components, because the NullComponentPeer
> implements requestFocus() as no-op. With my change, we would still call
> the HW peer, which causes callback into the KFM. However, I am not sure
> this matters as the KFM seems to reject such requests. If this is an
> issue this could be solved by checking isLightweight() before calling
> into the peer.

yep, most likely you can workaround this by this check, but I think it
will be more safe to perform the refactoring
in peer code (at least as the first step).  Unfortunately focus code
always was (and now is) rather fragile, so
less changes, less regressions.  If you will move the code to java.awt
you will have to spend much more time
with testing.

> Another concern is that the requestFocus() is overridden in 1 or 2 other
> places like WFileDialogPeer to implement no-op. I am not sure what is
> the issue here or the impact of my change. Any ideas?

file dialog on Windows is implemented using native dialog and we do
not support focus requests for it.

Oleg.

>
>
> Regards, Roman
>
>>
>> Roman,
>>
>> Nevertheless, this was my comment (which I mentioned in the previous post), I think the fix is fine
>> =) (if only Oleg doesn't provide another concern).
>>
>> Thanks,
>> Anton.
>>
>>
>> >> Regards, Roman
>> >>
>> >> Am Montag, den 14.11.2011, 22:35 +0100 schrieb Roman Kennke:
>> >>> Hi there,
>> >>>
>> >>> One thing that's bugging me for a while is how the ComponentPeer's
>> >>> requestFocus() method is supposed to work. As far as I could figure out,
>> >>> it's basically always like this (I use KFMHelper to call the
>> >>> corresponding KeyboardFocusManager's private methods by reflection):
>> >>>
>> >>>      public boolean requestFocus(Component lightweightChild, boolean
>> >>> temporary,
>> >>>              boolean focusedWindowChangeAllowed, long time, Cause cause)
>> >>> {
>> >>>          if (KFMHelper.processSynchronousLightweightTransfer(window,
>> >>>                  lightweightChild, temporary, focusedWindowChangeAllowed,
>> >>> time)) {
>> >>>              return true;
>> >>>          }
>> >>>
>> >>>          int result = KFMHelper.shouldNativelyFocusHeavyweight(window,
>> >>>                  lightweightChild, temporary, focusedWindowChangeAllowed,
>> >>> time,
>> >>>                  cause);
>> >>>
>> >>>          switch (result) {
>> >>>          case KFMHelper.SNFH_FAILURE:
>> >>>              return false;
>> >>>          case KFMHelper.SNFH_SUCCESS_PROCEED:
>> >>>                      requestFocusImpl(window, lightweightChild,
>> >>> temporary,
>> >>>                                   focusedWindowChangeAllowed, time,
>> >>> cause);
>> >>>          case KFMHelper.SNFH_SUCCESS_HANDLED:
>> >>>              // Either lightweight or excessive request - all events are
>> >>>              // generated.
>> >>>              return true;
>> >>>          default:
>> >>>              return false;
>> >>>          }
>> >>>      }
>> >>>
>> >>> The only thing that really differs between implementations would be the
>> >>> requestFocusImpl() method call in the SNFH_SUCCESS_PROCEED case. The
>> >>> rest seems to be the same in all implementations, except that in one
>> >>> case (Windows I believe) it is done in JNI while in others (X11) it's
>> >>> done by reflection.
>> >>>
>> >>> I think this can be consolidated by doing the above directly in the
>> >>> KeyboardFocusManager, before calling the peer requestFocus(), and have
>> >>> the peer's requestFocus() only do the requestFocusImpl() handling. This
>> >>> way we could avoid duplicate code and avoid reflection/JNI altogether.
>> >>>
>> >>> Maybe I am missing something?
>> >>>
>> >>> If not, I would work on a patch to move the above KeyboardFocusManager
>> >>> calls into the KFM and have the peer only bothers with the part that is
>> >>> requestFocusImpl() in the above example. Does that sound reasonable? It
>> >>> would certainly make some things simpler in OpenJDK as well as Cacio and
>> >>> the JavaFX SwingView that I am working on.
>> >>>
>> >>> Best regards, Roman
>> >>>
>> >>>
>> >>>
>> >>
>>
>>
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