Hi all,
I'm running into a problem that has me stumped and I was hoping someone
could give me some pointers.
I'm working on an application that uses a custom ViewGroup (actually a
FrameLayout that contains a RelativeLayout) to render an event calendar.
The events inside the calendar are represented as views that are sized
according to the duration of the event and the size of the containing view.
I'm running into a problem that occurs when the containing FrameLayout is
resized. The current implementation removes all of the views that represent
the events and attempts to add new ones and calculate their sizes based on
the current size of the FrameLayout. This work is being triggered via the
onSizeChanged() method of View which is overridden in the FrameLayout.
When the view is resized, this code is executed and the views are updated,
however, none of them actually render on the screen... the views contained
within the FrameLayout are simply not visible. If I load the view in the
hierarchyviewer tool, they are part of the view tree, and are outlined in
the overview in the positions they should be in, but they do not display.
(Note that the views are visible on the initial render of the FrameLayout...
it's only after a resize that they disappear.)
It appears that the order of events during the resize is as follows:
onMeasure()
onMeasure()
onSizeChanged()
onLayout()
Calling requestLayout() after resetting the views (inside onSizeChanged())
seems to have no effect. However, if I cause some delay before calling
requestLayout(), the views become visible. I can cause this delay by
spawning a thread and sleeping, or by creating a dummy button that simply
calls requestLayout() and pressing it after the resize myself, or even this
ugly hack placed at the end of onSizeChanged():
post(new Runnable() {
public void run() {
requestLayout();
}
});
When I use this hack, the contained views are visible, and the order of
events is as follows:
onMeasure()
onMeasure()
onSizeChanged()
onLayout()
onMeasure()
onMeasure()
onLayout()
So it appears that forcing a second measure pass (after the view tree has
been modified) makes the contained views visible as they should be. Why
delaying the call to requestLayout() does this is a mystery to me.
Can anyone provide any pointers as to what I'm doing wrong?
I realize that this is somewhat difficult to follow without looking at some
code, so I have created a small sample application that exhibits my issue
and made it available on Github:
https://github.com/MichaelSims/ViewGroupResizeTest
The hack I mentioned above is committed to a separate branch:
https://github.com/MichaelSims/ViewGroupResizeTest/tree/post-runnable-hack
If I can provide any additional information, please let me know and thanks
in advance.
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