UPDATE: Added handleOpenURL to the flow charts. Added UIApplicationExitsOnSuspend. Untangled some lines.
UPDATE: renamed deprecated handleOpenURL to newer name.
Now that we all are moving our source code gradually to iOS 4 I had to pause and think a bit about where to move which code. A problem that I’m facing frequently when updating a project is that the didFinishLaunching is only called if the app really launches.
That poses a bit of a challenge if you are used to doing things like refreshing images or other files off the internet. An app that is resumed from standby does no longer go through this delegate method. So an app that would always show fresh content upon launch before 4.0 multitasking would no longer load any new content as soon as you build it for 4.0. That’s actually one of the main reasons why I have not yet had time to update MyAppSales to 4.0.
To gain the possibility for “fast app switching” you actually don’t need to do anything. All apps automatically support it because they no longer get terminated if the user pushes the Home button. They get put into a sleep mode while the iPhone still has enough memory for everything else. It’s only if RAM runs out that the OS starts killing apps. There is begins with the ones that have the most memory reserved.
I grabbed the free trial of Omnigraffle and the Non-techie Process Flowchart Stencils by gfraser. Then I researched when all these various delegate methods of UIApplication are being called and drew charts to illustrate the flow.
By inhaling first how it was before multitasking and then upgrading your mental process to backgrounding we can begin to fully appreciate how it all fits together.