Reload application data when the app comes into foreground?

Question

I'm new to iPhone development. I'm building an app that loads data from a local sqlite3 DB in

-   (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {   

When I tap the iPhone button and put it in the background and then I recall it I see (as normal) the app in the same way I left it. What I would like to do is, when it comes in the foreground, to reload data as if it was called from scratch.

Which is the correct way to do it?
Thanks in advance.

Answer 1

So in the App Delegate class - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions will only be called at the first time you enter the app.Then it will call - (void)applicationDidBecomeActive:(UIApplication *)application.

If your iphone iOS is 4.0 or later, when a user click on the home button, it will first invoke - (void)applicationWillResignActive:(UIApplication *)application, then - (void)applicationDidEnterBackground:(UIApplication *)application.

Then the app will run in background till the user kill it. When the user enter the app again, it will first invoke - (void)applicationWillEnterForeground:(UIApplication *)application, then - (void)applicationDidBecomeActive:(UIApplication *)application.

So related to your question, you should call either applicationWillEnterForeground: or applicationDidBecomeActive: to reload your data. Though in the xcode's comment of these methods, Apple suggests use applicationDidBecomeActive: to restart paused tasks and/or update user interface; while in the applicationWillEnterForeground:, you can undo the changes you've made in entering the background.

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So to make it easier to see, i put a number tag to each method. Here's when the method to be called.

0 application:(UIApplication *)application didFinishLaunchingWithOptions: 
1 applicationDidBecomeActive: 
2 applicationWillResignActive: 
3 applicationDidEnterBackground: 
4 applicationWillEnterForeground: 

• First enter the app: call 0, then 1;

• Hit home button: call 2, then 3;

• Double hit home button(multitasking): call 2;

  • if user choose another app or hit home button again: call 3;

  • if user double hit home button again: call 1;

• Enter app again: call 4, then 1;