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.