Question

I am creating a simple application which perform some task on main thread. I am printing process in NSLog so I can understand that my process is running or not.

Now when I press home button without starting the process (Process will be start when I tap on a button) application enters in background and my both of methods applicationDidEnterBackground & applicationWillResignActive are being called.

But when I first tap on my button and process starts on main thread after that if I press home button none of these two method being called. So my application can’t know that app entered in background or not.

Even after that when I again active the app it shows me a black screen with status bar only.

1. Why this is happening?
2. Why app not entering in background?
3. Why apple’s methods not being called?
4. Is there a way to solve it?

UPDATE
Here is my appdelegate class code

- (void)applicationWillResignActive:(UIApplication *)application
{

}

- (void)applicationDidEnterBackground:(UIApplication *)application
{
}

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

}

- (void)applicationDidBecomeActive:(UIApplication *)application
{

}

All methods have no implementation.

Thanks in advance.

Answer 1

I am creating a simple application which perform some task on main thread.

Don’t perform long-running operations on the main thread.

The delegate callbacks happen on the main thread. If the main thread is busy, then the callbacks won’t happen until you return to the “run loop”.

When foregrounding your app, the OS actually displays a screenshot if available, falling back to the launch image (Default.png). The screenshot is taken after -applicationDidEnterBackground: returns, which allows you to customize what gets saved (you might want to do this for security reasons, or to hide UI elements which might not make sense to show when relaunching e.g. a countdown timer).

The black screen is probably because your app has no launch image. If your app takes more than about 10 seconds to enter the background (and it does, since the main thread is blocked), it gets killed. Except the debugger is attached and catches SIGKILL, so it’s easy to miss unless you’re watching Xcode.