Smooth UI changes in cocoa-applescript (Xcode) - xcode

Question

I'm trying to write a simple Xcode cocoa-applescript program that executes a bash script on each subfolder of a folder and shows a progressbar while doing it.
I have a NSProgressIndicator set up to be linked to barStatus and well a NSTextField to be linked to lblStatus to show some informative text:
property barStatus : missing value
property lblStatus : missing value
this is the loop where the main action takes place:
tell application "Finder" to set subfolders to every folder of folder macPath
barStatus's setIndeterminate_(false)
barStatus's setDoubleValue_(0)
barStatus's setMaxValue_(count of subfolders)
repeat with eachFolder in subfolders
set posixPath to (POSIX path of (eachFolder as text)) as text
-- set text of progress indicator text
lblStatus's setStringValue_("Resizing '" & ( do shell script "basename \"" & (posixPath) & "\" | sed \"s/^.*_//\"" ) & "'...")
delay 0.5
-- do the shell script
do shell script "bash ~/.uploader/image.sh \"" & posixPath & "\""
-- step the indicator
barStatus's incrementBy_(1)
end repeat
lblStatus's setStringValue_("Done!")
All seems to work properly, yet the UI is somewhat glitchy. Instead of just increasing smoothly, the progressbar disappears on each step and gets shown for a short while, then dissappears again. The text in lblStatus does get changed smoothly.
Things get totally lost when I remove the delay from the loop: no UI changes are made (even though the scripts get run properly) until the loop is finished. So the progressbar just dissappears and reappears filled out when the loop is done.
Here's a youtube video of the flickery UI.
What am I doing wrong? How can I have xcode draw the progressbar smoothly?
Note that this is the first time I write an Xcode app, and that my knowledge of Applescript is somewhat sketchy.
EDIT:
I found that calling the function that processes the same function does not have a flickery UI when called form a menu item (or with a key combo bound to that menu item).

Answer 1

I'm not sure why the progress bar hides itself. Did you bind the visible property of it to something that may make it hide?
Things get totally lost when I remove the delay from the loop: no UI
changes are made
In general though when "no UI changes are made" it's because the application is too busy on the main thread to update the interface items in real time. All of your code is running on the main thread. You need to make some of it happen on a background thread. As such I have 2 suggestions for you to try.
First try using the progress bar's method "setUsesThreadedAnimation:". Add this just above your repeat loop...
barStatus's setUsesThreadedAnimation_(true)
Second, if that doesn't help then try moving your repeat loop work onto a background thread (using NSThread's detachNewThreadSelector:)... but make the interface updates happen on the main thread. I don't know ApplescriptObjC language so the following code is probably completely wrong. You'll have to write it properly but it will show you the idea...
[NSThread detachNewThreadSelector:#selector(processFolderListOnBacgroundThread_) toTarget:self withObject:subfolders];
-- this will happen on the main thread
on updateProgressBarByOne_()
barStatus's' incrementBy_(1)
end updateProgressBarByOne_
-- this will happen on the main thread
on updateStatusTextWithText_(statusText)
lblStatus's' setStringValue_(statusText)
end updateInterfaceItemsOnMainThreadWithObject_
-- this will happen on a background thread
on processFolderListOnBacgroundThread_(subFolders)
repeat with eachFolder in subfolders
set posixPath to (POSIX path of (eachFolder as text)) as text
-- set text of progress indicator text
my updateStatusTextWithText_("Resizing '" & ( do shell script "basename \"" & (posixPath) & "\" | sed \"s/^.*_//\"" ) & "'...")
-- do the shell script
do shell script "bash ~/.uploader/image.sh \"" & posixPath & "\""
-- step the indicator
my updateProgressBarByOne_()
end repeat
my updateStatusTextWithText_("Done!")
end processFolderListOnBacgroundThread_
If you use the background thread approach you'll probably have to make the buttons in your interface inactive while the background thread is working (so the user can't press them and start a new task). So just set their enabled property to false prior to calling "detachNewThreadSelector:" and enable them again after the work is finished. You can do this by having another handler which enables them and call that from the end of the background thread code.