Load time issues FLEX swf vs. FLASH swf

Question

Hello,
We are building FLex and Flash apps running on Flash 10.1.  In our situation, the load time for a 1080x768 swf is slower when building in Flex than in flash.  We have tried useing the preinitialize event to set at least a loading message, but the delay happens before the preinitialize event.  It seems to take 1-2 seconds to load the FLex API perhaps?  The only visula we can see is the background color of the stage.  Even with a simple nearly empty main canvas, the load is slow enough to be noticable.  More importanly it is faster when using a FLASH swf ( or pure AS3), so it must be related to the FLex aspect.  Is there anyway to cache the common classes or maybe exclude some that are not used?
Thanks,
Jeff Schuenke

Answer 1

The main point of RSLs is to gamble on improving download time of the SWF at
networks speeds.  The gamble is that someone has already loaded the RSL so
it gets picked up off the browser cache at hard-drive speeds.  If it isn't
true, you pay a higher penalty because you are loading an RSL that has code
in it you aren't using.  That's why the total payload is more.  For the
record, only the SWF or the SWZ gets loaded, not both.  But even then the
total payload would be more.
At home, my DSL/WIFI network gets me about 70KB/sec, so saving 300K would be
a noticable savings.  If you are loading off a hard disk, 300K probably
won't be felt.
The startup sequence of a SWF over a network (http or https):
-start streaming in SWF bytes
-when the first frame is downloaded (generally about 80-100K) see how many
bytes are left to download and if there is a lot, show a progress bar
-load any RSLs and wait for their download and initialization
-update the progress bar until the rest of the SWF downloads
-after the SWF downloads:
    -initialize styles
    -initialize resources
    -prepare embedded fonts
    -setup managers for popups, tooltips, dragging if needed
    -instantiate Application
        -verify and initialize all classes needed by Application
        -dispatch Application preinitialize
        -instantiate the initial set of children for the Application
        -dispatch Application initialize
    -update progress bar to show "initializing"
    -start validation of Application and its children
    -continue to do so until all children are measured and layed out
    -dispatch Application creationComplete
    -add Application to stage (actually systemManager)
    -dispatch Application applicationComplete
The startup sequence of a SWF on a hard drive is different.  The entire SWF
must be sucked into memory, unzipped (SWFs are zipped by default) and only
then do we get to the steps where we show a progress bar, check for RSLs,
etc.
At 3MB, there might be a noticeable hit.  You can find a big image file and
zip it to see if it comes out to about 3MB.  Then use the file system to
copy it and see how long that takes and then unzip it and see how long that
takes.
Another place that causes delay is in the validation of children.  If the
children's size are not stable right away (because data is coming in that
affects their size) then several validation passes might be taking place.
A common error is to create every child in the app, even ones that aren't
seen or needed right away.  That adds work at validation time and delays the
startup process.
I would recommend that you use the performance profiler in Flex Builder to
see where all the time is being spent.
However, 3MB is a big SWF. Use of modules to chop off stuff not needed until
"later" is recommended and will probably be the answer.