What is the last function in iPhone application lifecycle

Question

Before my application is going to be closed I have to logout user from web service. And I can't find the very last function that is invoked before application die?

-(void)LogoutUser
{    
    int userId = [[GlobalData sharedMySingleton] getUserId];

    NSString *soapMsg = 
    [NSString stringWithFormat:
     @"<?xml version=\"1.0\" encoding=\"utf-8\"?>...", userId
     ];

    NSURL *url = [NSURL URLWithString: @"http://....asmx"];     

    NSMutableURLRequest *req = [NSMutableURLRequest requestWithURL:url];    
    NSString *msgLength = [NSString stringWithFormat:@"%d", [soapMsg length]];

    [req addValue:@"text/xml; charset=utf-8" forHTTPHeaderField:@"Content-Type"];   
    [req addValue:@"http://..." forHTTPHeaderField:@"SOAPAction"];  
    [req addValue:msgLength forHTTPHeaderField:@"Content-Length"];   
    [req setHTTPMethod:@"POST"];
    [req setHTTPBody: [soapMsg dataUsingEncoding:NSUTF8StringEncoding]];

    conn = [[NSURLConnection alloc] initWithRequest:req delegate:self];

    if (conn) 
    {
        webData = [[NSMutableData data] retain];
    }     

}

-(void) connection:(NSURLConnection *) connection didReceiveResponse:(NSURLResponse *) response 
{
    [webData setLength: 0];
}

-(void) connection:(NSURLConnection *) connection didReceiveData:(NSData *) data 
{
    [webData appendData:data];  
}

-(void) connection:(NSURLConnection *) connection didFailWithError:(NSError *) error 
{   
    [webData release];    
    [connection release];
}

-(void) connectionDidFinishLoading:(NSURLConnection *) connection 
{   
    NSString *theXML = [[NSString alloc] 
                        initWithBytes: [webData mutableBytes] 
                        length:[webData length] 
                        encoding:NSUTF8StringEncoding];    


    [theXML release];    

    [connection release];
    [webData release];   
}

Answer 1

There are two places you'll need to trigger your logout code from, both of which are detailed in the UIApplicationDelegate Protocol Reference documentation.

For pre-iOS 4 devices (and to cover other circumstances) you should use:

- (void)applicationWillTerminate:(UIApplication *)application

As Apple puts it:

For applications that do not support background execution or are linked against iOS 3.x or earlier, this method is always called when the user quits the application. For applications that support background execution, this method is generally not called when the user quits the application because the application simply moves to the background in that case. However, this method may be called in situations where the application is running in the background (not suspended) and the system needs to terminate it for some reason.

However, you'll need to use...

- (void)applicationDidEnterBackground:(UIApplication *)application

...on iOS 4+ devices, as (once again from the Apple docs):

In iOS 4.0 and later, this method is called instead of the applicationWillTerminate: method when the user quits an application that supports background execution

That said, irrespective of all the above, you'll most likely want to logout of the web service when your app is backgrounded and log back in when it's "woken up" as well. See the above mentioned applicationDidEnterBackground: method and the applicationWillEnterForeground: method documentation for more details.

Answer 2

- (void)applicationDidEnterBackground:(UIApplication *)application {
/*
 Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later. 
 If your application supports background execution, called instead of applicationWillTerminate: when the user quits.
 */
}

this may be not a last function but. you can do logout here.

Answer 3

For typical apps under iOS 4.x, applicationWillResignActive and perhaps applicationDidEnterBackground will be called both before your app is terminated (at some unknown time in the future), and at other times as well when the app isn't being terminated. However it might be a good idea to log out here, as your app may never get any further CPU run time.

If you have pending network activity, such as trying to logout, you might want to use the multitasking call beginBackgroundTaskWithExpirationHandler: to request a bit of additional time in the background to finish the log out process, such as handshaking with any network callbacks required.