Any tips on how to create apps that run on iOS 3 and iOS 4?

I'm developing an iPhone application and my target is 3GS and 4G devices.
iOS 4 introduces methods thats deal with multitasking and newer methods to deal with foreground/background lifecycle events.
These new methods aren't available in iOS 3 which simply quits the app and doesn't run it in the background.
Any tips on how to create apps that run on iOS 3 and iOS 4?

-------------Problems Reply------------

The iPad Programming Guide (I know, not what you'd expect) has a section on universal apps that shows you how to check that symbols exist at runtime. It applies to your question as well.

Start here:

I put all my ios4 functions in one section, then wrap a compiler macro(so xcode lets you compile) around them and have functional checking inside each function(so once compiled, your code runs without crashing).. for example

//Define Logic for conditional code based on version of iOS
- (void)applicationDidEnterBackground:(UIApplication *)application {
//SPECIAL CASE:For OS versions before 4.0, background processes are not supported
if (backgroundSupported) {

- (void)applicationWillEnterForeground:(UIApplication *)application {
if (backgroundSupported) {
if (backgroundSupported) {

- (BOOL)checkBackgroundSupported {
UIDevice* device = [UIDevice currentDevice];
backgroundSupported = NO;
if ([device respondsToSelector:@selector(isMultitaskingSupported)])
backgroundSupported = device.multitaskingSupported;
return backgroundSupported;

Category:iphone Views:7 Time:2010-09-30
Tags: iphone apple ios4

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