Understanding iOS 4 Backgrounding and Delegate Messaging

The World Before Multitasking

The first thing that I learned from this is that applicationDidBecomeActive: is being called right after application:didFinishLaunchingWithOptions:. So even before 4.0 it would have been smart to put there any kind of code that you want executed whenever the app becomes active, be it after app start or upon rejecting a phone call.

Not shown on this diagram is the situation that your app is eating up all the system memory and ignores both the level 1 and level 2 memory warnings. In that case the OS will also terminate your app without totally unscrupulous.

The mechanism with WillResignActive and DidBecomeActive is sort of the Backgrounding Lite that has always been there. This occurs whenever some other thing is displayed in front of your app. This could be the UI to accept a phone call or something as benign as the synching screen.

Multitasking ON

Adding multitasking to this flow chart makes it about twice as complex. I probably spent an hour trying to fit it all together with no crossing lines. Another thing that I noticed while doing this is that applicationWillResignActive: is the only delegate method that I could not optimize into a single box, because one use is to show that the app has been interrupted, the other is to the path into the background.

An app built with 3.2 will still go through a short background stage where applicationDidEnterBackground: is called. but then it will be terminated as usual. If the same app is built against a 4.x SDK then it will not go straight from background to being terminated. Instead it will stick around and so will be the debugger. As soon as you tap the app icon again or choose it from the app switcher it is first informed that applicationWillEnterForeground and then applicationDidBecomeActive.

An app that is suspended but still in RAM might be terminated by the OS if memory runs low. But after entering the background there is no longer any delegate method being called, instead the app will receive a KILL signal. This occurs also if the user long-presses the app icon in app switcher and then removes the app from there with the removal button.

Accepting a phone call no longer terminates your app but will send it into the appropriate background mode. Within the background box you see two purple states that the app can be in. All apps are suspended in RAM per default. You might want to slim down your memory footprint to make your app a less likely target for killing if the system runs low on memory.

Only apps that actually require background processing continue to be executing. This requirement is either set in info.plist or by telling the OS that you have a task to complete, like for example a file upload.

The following kinds of activities get to run in true multi tasking behind the foreground app with lesser CPU priority.

• playing music: “App plays audio”
• geo location: “App registers for location updates”
• VOIP: “App provides Voice over IP services”

If your app does one of these things then adding the key to info.plist is all it takes. But be aware that as soon as your app stops doing what it stated it would be doing the OS again will send it to sleep, only to be awakend by another gentle tap by the user.

In background mode you’re advised to stop updating the UI. Especially with OpenGL Apple is really strict. If you app as much as touches OpenGL while in background the app gets killed right away.

There are only two scenarios left where your app’s applicationWillTerminate: will actually be called: if it’s build with an SDK of less than version 4.0 or if you chose to opt out of backgrounding by adding the UIApplicationExitsOnSuspend key to your info.plist.

So, let’s ask the question we’ve been doing all this fuss for: Where should you now put your code to initialize, update or save changes? applicationWillTerminate not being called in the majority of cases makes it a rather bad candidate to save user defaults or data.

Looking at the chart I see applicationDidEnterBackground as the ideal candidate delegate method for saving state. This is also the last method to be called before a regular 4.0 app gets put to sleep and before a possible kill.

For updating data from the web the case is not as clear. You would not want to reload every time the user comes back to your app. Possible applicationDidBecomeActive: is a good place, provided that you only reload data if sufficient time has passed to be able to assume that something new is available.

Only the first loading of data can stay in application:didFinishLaunchingWithOptions: since every call applicationDidBecomeActive: most likely has the data already loaded previously.

Conclusion

Adding fast app switching and multitasking support is quite easy since for the most part you don’t need to do anything. But you WILL have to review the contents of your app delegate methods to see which code has to be moved into one of the other delegate methods now. Clean out applicationWillTerminate: and have a close look at application:didFinishLaunchingWithOptions: to check if you have something in there that needs to be done every time the app becomes active.

These charts come from some experimentation that I did and what I remembered from the WWDC 2010 session videos on multitasking. Potentially there are mistakes or more surprises hidden in there. Please let me know if you find any.

Here’s the chart in PDF format in case you want to print it out and frame it.

source

WWDC 2010 is Sold Out Already

Apple is indicating that tickets for WWDC 2010 are sold out just eight days after being announced.

The Worldwide Developers Conference (WWDC) takes place June 7 through June 11 at San Francisco’s Moscone West. The five-day conference includes the first ever iPad development sessions and hands-on working labs for iPhone OS 4, as well as Mac OS X core technology labs.

Apple is widely expected to annnounce the new fourth generation iPhone at the event.

iclarified.com

An A-Z Index of the Apple OS X Command Line

a

 alias     Create an alias •
alloc     List used and free memory
apropos   Search the whatis database for strings
awk       Find and Replace text within file(s)
b
basename  Convert a full pathname to just a filename
bash      Bourne-Again SHell
bg        Send to background •
bind      Display readline key and function bindings •
bless     Set volume bootability and startup disk options.
break     Exit from a For, While, Until or Select loop •
builtin   Execute a shell builtin •
bzip      Compress or decompress files
c
cal       Display a calendar
caller    Return the context of a subroutine call •
case      Conditionally perform a command •
cat       Display the contents of a file
cd        Change Directory •
chflags   Change a file or folder's flags
chgrp     Change group ownership
chmod     Change access permissions
chown     Change file owner and group
chroot    Run a command with a different root directory
cksum     Print CRC checksum and byte counts
clear     Clear terminal screen
cmp       Compare two files
comm      Compare two sorted files line by line
command   Run a command (not a function) •
complete  Edit a command completion [word/pattern/list] •
continue  Resume the next iteration of a loop •
cp        Copy one or more files to another location
cron      Daemon to execute scheduled commands
crontab   Schedule a command to run at a later date/time
cut       Divide a file into several parts
d
date      Display or change the date & time
dc        Desk Calculator
dd        Data Dump - Convert and copy a file
declare   Declare variable & set attributes •
defaults  Set preferences, show hidden files
df        Display free disk space
diff      Display the differences between two files
diff3     Show differences among three files
dig       DNS lookup
dirname   Convert a full pathname to just a path
dirs      Display list of remembered directories •
diskutil  Disk utilities - Format, Verify, Repair
disown    Unbind a job from the current login session •
ditto     Copy files and folders
dot_clean Remove dot-underscore files
drutil    Interact with CD/DVD burners
dscacheutil Query or flush the Directory Service/DNS cache
dscl      Directory Service command line utility
du        Estimate file space usage
e
echo      Display message on screen •
ed        A line-oriented text editor (edlin)
enable    Enable and disable builtin shell commands •
env       Set environment and run a utility
eval      Evaluate several commands/arguments •
exec      Execute a command •
exit      Exit the shell •
expand    Convert tabs to spaces
expect    Programmed dialogue with interactive programs
         Also see AppleScript
export    Set an environment variable •
expr      Evaluate expressions
f
false     Do nothing, unsuccessfully
fc        Fix command (history)
fdisk     Partition table manipulator for Darwin UFS/HFS/DOS
fg        Send job to foreground •
file      Determine file type
find      Search for files that meet a desired criteria
fmt       Reformat paragraph text
fold      Wrap text to fit a specified width
for       Loop command •
fsck      Filesystem consistency check and repair
fsaclctl  Filesystem enable/disable ACL support
fs_usage  Filesystem usage (process/pathname)
ftp       Internet file transfer program
g
GetFileInfo Get attributes of HFS+ files
getopt    Parse positional parameters
getopts   Parse positional parameters •
goto      Jump to label and continue execution
grep      Search file(s) for lines that match a given pattern
groups    Print group names a user is in
gzip      Compress or decompress files
h
hash      Refresh the cached/remembered location of commands •
head      Display the first lines of a file
hdiutil   Manipulate iso disk images
history   Command History •
hostname  Print or set system name
i
id        Print user and group names/id's
if        Conditionally perform a command •
info      Help info
install   Copy files and set attributes
j
jobs      List active jobs •
join      Join lines on a common field
k
kextfind  List kernel extensions
kickstart Configure Apple Remote Desktop
kill      Stop a process from running
l
l         List files in long format (ls -l)
last      Indicate last logins of users and ttys
launchctl Load or unload daemons/agents
ll        List files in long format, showing invisible files (ls -la)
less      Display output one screen at a time
let       Evaluate expression •
lipo      Convert a universal binary
ln        Make links between files (hard links, symbolic links)
local     Set a local (function) variable •
locate    Find files
logname   Print current login name
login     log into the computer
logout    Exit a login shell (bye) •
lpr       Print files
lprm      Remove jobs from the print queue
lpstat    Printer status information
ls        List information about file(s)
lsregister Reset the Launch Services database
lsbom     List a bill of materials file
lsof      List open files
m
man       Help manual
mdfind    Spotlight search
mdutil    Manage Spotlight metadata store
mkdir     Create new folder(s)
mkfifo    Make FIFOs (named pipes)
more      Display output one screen at a time
mount     Mount a file system
mv        Move or rename files or directories
n
net       Manage network resources
netstat   Show network status
networksetup Network and System Preferences
nice      Set the priority of a command
nohup     Run a command immune to hangups
ntfs.util NTFS file system utility
o
onintr    Control the action of a shell interrupt
open      Open a file/folder/URL/Application
osacompile Compile Applescript
osascript Execute AppleScript
p
passwd    Modify a user password
paste     Merge lines of files
pbcopy    Copy data to the clipboard
pbpaste   Paste data from the Clipboard
pico      Simple text editor
ping      Test a network connection
pkgutil   Query and manipulate installed packages
plutil    Property list utility
pmset     Power Management settings
popd      Restore the previous value of the current directory •
pr        Convert text files for printing
printenv  Print environment variables
printf    Format and print data •
ps        Process status
pushd     Save and then change the current directory
pwd       Print Working Directory •
q
quota     Display disk usage and limits
r
rcp       Copy files between machines
read      Read one line from standard input •
readonly  Mark a variable or function as read-only •
reboot    Stop and restart the system
return    Exit a function •
rev       Reverse lines of a file
rm        Remove files
rmdir     Remove folder(s)
rpm       Remote Package Manager
rsync     Remote file copy - Sync file tree (also RsyncX)
s
say       Convert text to audible speech
screen    Multiplex terminal, run remote shells via ssh
screencapture Capture screen image to file or disk
sdiff     Merge two files interactively
security  Administer Keychains, keys, certificates and the Security framework
sed       Stream Editor
select    Generate a list of items •
set       Set a shell variable = value •
setfile   Set attributes of HFS+ files
shift     Shift positional parameters •
shopt     Set shell options •
shutdown  Shutdown or restart OS X
sleep     Delay for a specified time
softwareupdate System software update tool
sort      Sort text files
source    Execute commands from a file •
split     Split a file into fixed-size pieces
stop      Stop a job or process
su        Substitute user identity
sudo      Execute a command as another user
sum       Print a checksum for a file
suspend   Suspend execution of this shell •
sw_vers   Print Mac OS X operating system version
system_profiler  Report system configuration
systemsetup Computer and display system settings
t
tail      Output the last part of files
tar       Tape ARchiver
tee       Redirect output to multiple files
test      Condition evaluation •
textutil  Manipulate text files in various formats (Doc,html,rtf)
time      Measure Program Resource Use
times     Print shell & shell process times •
touch     Change file timestamps
tr        Translate, squeeze, and/or delete characters
trap      Execute a command when the shell receives a signal •
traceroute Trace Route to Host
true      Do nothing, successfully
tty       Print filename of terminal on stdin
type      Describe a command •
u
ufs.util  Mount/unmount UFS file system
ulimit    limit the use of system-wide resources •
umask     Users file creation mask
umount    Unmount a device
unalias   Remove an alias •
uname     Print system information
unexpand  Convert spaces to tabs
uniq      Uniquify files
units     Convert units from one scale to another
unset     Remove variable or function names •
until     Loop command •
users     Print login names of users currently logged in
uuencode  Encode a binary file
uudecode  Decode a file created by uuencode
uuidgen   Generate a Unique ID (UUID/GUID)
uucp      Unix to Unix copy
v
vi        Text Editor
w
wait      Wait for a process to complete •
wc        Print byte, word, and line counts
whatis    Search the whatis database for complete words
where     Report all known instances of a command
which     Locate a program file in the user's path
while     Loop command •
who       Print all usernames currently logged on
whoami    Print the current user id and name (`id -un')
write     Send a message to another user
x
xargs     Execute utility - passing arguments
yes       Print a string until interrupted

Commands marked • are bash built-in commands.
OS X Panther 10.3, Tiger 10.4 and Leopard 10.5 default to running the bash shell, this runs under 'Darwin' the open source core of OSX

ss64.com/osx/

Apple Worldwide Developers Conference Kicks Off June 7 in San Francisco

The “center of the app universe” will be at Moscone West in San Francisco this year, as WWDC10 kicks off on June 7 and runs through the 11th.

In a press release, Senior Apple VP Scott Forstall doesn’t even pretend it’s about the Mac anymore. WWDC will provide “in-depth sessions and hands-on working labs to learn more about iPhone OS 4,” helping developers “make their iPhone and iPad apps even better.”

And it doesn’t end there, unless we’re talking about information on the next iteration of Mac OS X.

For developers, the $1,599 package gets you in on five technology tracks: Application Frameworks; Internet & Web; Graphics & Media; Developer Tools; and Core OS, but no IT/SysAdmin track. The sessions offer blanket coverage of iPhone OS development, but unless OS X 10.7 sessions will be super secret, there doesn’t appear to be a lot there. It sure seems telling that five design awards will be handed out for the iPhone and the iPad, but not the Mac.

For those who are not developers, expect to see the next generation iPhone, rumored to be named the iPhone HD. If the infamous prototype revealed by Gizmodo is the final version, its hardware features will include: a front-facing video camera, camera flash, micro-SIM card, and two volume buttons. Also, John Gruber has suggested the resolution of the display will jump to 960×640. The launch date for the phone will certainly be announced, probably June or early July.

That phone will be running iPhone OS 4, of course, which has already been previewed. There may be a few new features, along with information about a “unity release” of iPhone OS 4.1 for the iPhone, iPod touch, and iPad sometime in late summer or early fall.

theappleblog.com

My first iPhone web app

This is the first time I learn making web app for iphone. So check it out yo! You can find the tutorial on theappleblog.com. I use iwebkit. This is the screenshots from my mac.



This is the copy of my code if you want to take a look at it. Use dashcode to edit it.