I'm trying to use the structure laid out in LunarLander to create a
simple game in which the user can drag some bitmaps around on the
screen (the actual game is more complex, but that's not important). I
ripped out the irrelevant parts of LanderLander, and set up my own
bitmap drawing, something like
In BoardThread (an inner class of BoardView):
run()
{
while(mRun)
{
canvas = lockSurfaceHolder...
syncronized(mSurfaceHolder)
{
/* drawStuff using member position fields
in BoardView */
}
unlockSurfaceHolder
}
}
My drawStuff simply walks through some arrays and throws bitmaps onto
the canvas. All that works fine. Then I wanted to start handling touch
events so that when the user presses a bitmap, it is selected, when
the user unpresses a bitmap, it is deselected, and if a bitmap is
selected during a touch move event, the bitmap is dragged. I did this
stuff by listening for touch events in the BoardView's parent,
BoardActivity, and passing them down into the BoardView. Something
like
In BoardView
handleTouchEvent(MotionEvent e)
{
synchronized(mSurfaceHolder)
{
/* Modify shared member fields in BoardView
so BoardThread can render the bitmaps */
}
}
This ALSO works fine. I can drag my tiles around the screen no
problem.
However, every once in a while, when the app first starts up and I
trigger my first touch event, the handleTouchEvent stops executing at
the synchronized line (as viewed in DDMS). The drawing loop is active
during this time (I can tell because a timer changes onscreen), and it
usually takes several seconds or more before a bunch of touch events
come through the pipeline and everything is fine again.
This doesn't seem like deadlock to me, since the draw loop is
constantly going in and out of its syncronized block. Shouldn't this
allow the event handling thread to grab a lock on mSurfaceHolder?
What's going on here? Anyone have suggestions for improving how I've
structured this?
Some other info. This "hang" only ever occurs on first touch event
after activity start. This includes on orientation change after
restoreState has been called. Also, I can remove EVERYTHING within the
syncronized block in the event handler, and it will still get hung up
at the syncronized call.
Thanks!
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