Need help: My program should react when an other class is doing something specific - Not as easy as it sounds

Question

Hello, I´m writing an program that uses twitter. I want that my app shows an UIAlertView when the user presses on the "Tweet"-Button and the username or password is wrong. For my Twitterfunction I use the TwitterRequest.m/h from Brandon Trebitowski. If everthing works great and the username/password is right, this happens in my app:

        TwitterRequest * t = [[TwitterRequest alloc] init];
        (...);
        [t statuses_update:twittermessage.text delegate:self requestSelector:@selector(status_updateCallback:)];

        loadingActionSheet = [[UIActionSheet alloc] initWithTitle:@"Posting to Twitter..." delegate:nil 
                                                cancelButtonTitle:nil destructiveButtonTitle:nil otherButtonTitles:nil];
        [loadingActionSheet showInView:self.view];
    }


    - (void) status_updateCallback: (NSData *) content {
        [loadingActionSheet dismissWithClickedButtonIndex:0 animated:YES];
        [loadingActionSheet release];
        NSLog(@"%@",[[NSString alloc] initWithData:content encoding:NSASCIIStringEncoding]);
    }

But how can I show an UIAlertView when the username/password was wrong? Here is the TwitterRequest.m:

#import "TwitterRequest.h"

@implementation TwitterRequest

@synthesize username;
@synthesize password;
@synthesize receivedData;
@synthesize delegate;
@synthesize callback;
@synthesize errorCallback;

-(void)friends_timeline:(id)requestDelegate requestSelector:(SEL)requestSelector{
    isPost = NO;
    // Set the delegate and selector
    self.delegate = requestDelegate;
    self.callback = requestSelector;
    // The URL of the Twitter Request we intend to send
    NSURL *url = [NSURL URLWithString:@"http://twitter.com/statuses/friends_timeline.xml"];
    [self request:url];
}

-(void)statuses_update:(NSString *)status delegate:(id)requestDelegate requestSelector:(SEL)requestSelector; {
    isPost = YES;
    // Set the delegate and selector
    self.delegate = requestDelegate;
    self.callback = requestSelector;
    // The URL of the Twitter Request we intend to send
    NSURL *url = [NSURL URLWithString:@"http://twitter.com/statuses/update.xml"];
    requestBody = [NSString stringWithFormat:@"status=%@",status];
    [self request:url];
}

-(void)request:(NSURL *) url {
    theRequest   = [[NSMutableURLRequest alloc] initWithURL:url];

    if(isPost) {
        NSLog(@"ispost");
        [theRequest setHTTPMethod:@"POST"];
        [theRequest setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
        [theRequest setHTTPBody:[requestBody dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES]];
        [theRequest setValue:[NSString stringWithFormat:@"%d",[requestBody length] ] forHTTPHeaderField:@"Content-Length"];
    }

    theConnection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self];

    if (theConnection) {
        // Create the NSMutableData that will hold
        // the received data
        // receivedData is declared as a method instance elsewhere
        receivedData=[[NSMutableData data] retain];
    } else {
        // inform the user that the download could not be made
    }
}

- (void)connection:(NSURLConnection *)connection didReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge {
    //NSLog(@"challenged %@",[challenge proposedCredential] );

    if ([challenge previousFailureCount] == 0) {
        NSURLCredential *newCredential;
        newCredential=[NSURLCredential credentialWithUser:[self username]
                                                 password:[self password]
                                              persistence:NSURLCredentialPersistenceNone];
        [[challenge sender] useCredential:newCredential
               forAuthenticationChallenge:challenge];

    } else {
        [[challenge sender] cancelAuthenticationChallenge:challenge];
        // inform the user that the user name and password
        // in the preferences are incorrect
        NSLog(@"Invalid Username or Password"); //THIS MUST be important. The console shows this message, if the username/password is wrong. Here is also the place, where I set the bool to TRUE 
    }

}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    // this method is called when the server has determined that it
    // has enough information to create the NSURLResponse

    // it can be called multiple times, for example in the case of a
    // redirect, so each time we reset the data.
    // receivedData is declared as a method instance elsewhere
    //[receivedData setLength:0];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    //NSLog([[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding]);
    // append the new data to the receivedData
    // receivedData is declared as a method instance elsewhere
    [receivedData appendData:data];
}

- (void)connection:(NSURLConnection *)connection
  didFailWithError:(NSError *)error
{
    // release the connection, and the data object
    [connection release];
    // receivedData is declared as a method instance elsewhere
    [receivedData release];

    [theRequest release];

    // inform the user
    NSLog(@"Connection failed! Error - %@ %@",
          [error localizedDescription],
          [[error userInfo] objectForKey:NSErrorFailingURLStringKey]);

    if(errorCallback) {
        [delegate performSelector:errorCallback withObject:error];
    }
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    // do something with the data

    if(delegate && callback) {
        if([delegate respondsToSelector:self.callback]) {
            [delegate performSelector:self.callback withObject:receivedData];
        } else {
            NSLog(@"No response from delegate");
        }
    } 

    // release the connection, and the data object
    [theConnection release];
    [receivedData release];
    [theRequest release];
}

-(void) dealloc {
    [super dealloc];
}


@end

I know that the important line in the TwitterRequest.m is in the else-cause of the -(void)connection-methode, because the Console writes always Invalid Username or Password, when they are wrong. So I tried to make there a bool as propertey, which will be set to TRUE, when the name/password is wrong(= when the else-cause will be used). In my ViewController I made this:

if (t.stimmtNicht == TRUE) {
    [loadingActionSheet dismissWithClickedButtonIndex:0 animated:YES];
    [loadingActionSheet release];
    UIAlertView *alert;
    alert = [[UIAlertView alloc] initWithTitle:@"Ouch!"
                                       message:@"Your Username or Password is wrong!"
                                      delegate:self 
                             cancelButtonTitle:@"OK" 
                             otherButtonTitles: nil];
    [alert show];   
    [alert release];
}

But he always doesn't use the if-cause, even if the password is wrong. I think the code go faster through the if-quere than the TwitterRequest set it to TRUE. What can I do?

Thanks for your help and sorry for this stupid question, but I'm learning Objective-C and programming in general since just one week and I don´t know correctly how to interact from my ViewController with other classes.

Also sorry for my bad English!

Answer 1

Two ways I can think of:

1. Apparently your TwitterRequest class has a "delegate" ivar; try calling the delegate to tell him (her?) that your credentials are wrong.
2. Send an NSNotification through the NSNotificationCenter

In both cases, the class who gets notified should display the login view (with the username and password fields), and that's it.