Question

There is one issue that I’ve been struggling with and I can’t seem to get enough information about it on the web. It has to do with the Apple multitasking and the Tab bar view. I want to control which tab will be selected when the application is entering foreground or becoming active.
At the moment every time I will close the app and re-open it, it will open the last UIView that was displaying on the tab bar. How can I control that?

Firstly, I want to be able to display a preview image with the app logo every time the application becomes active. Here is the code I’m using for that but I keep getting EXC_BAD_ACCESS when the app is entering foreground for this line: [window addSubview:self.preMiniView]:

   - (void)applicationDidBecomeActive:(UIApplication *)application {
    if (!self.preMiniView)
    {
        self.preMiniView = [[UIImageView alloc] initWithFrame:window.frame];    
        self.preMiniView.frame = CGRectMake(0,0,324,480);
        window.backgroundColor = [UIColor colorWithRed:21.0/255.0 green:7.0/255.0 blue:2.0/255.0 alpha:1];  
    }       
    UIImage *img = [UIImage imageNamed:@"preloadSm.jpg"];
    self.preMiniView.image = img;
    [img release];

    if (self.preMiniView.alpha == 0.0)
    {
        [self.preMiniView setAlpha:1.0];
    }

    [window addSubview:self.preMiniView];  // adding the how to view to the view.

    [NSTimer scheduledTimerWithTimeInterval:3 target:self selector:@selector(initApp:)
                                   userInfo:nil
                                    repeats:NO];
    }



      - (void)applicationDidEnterBackground:(UIApplication *)application 
       {
          [tabBarController.view endEditing:YES];

        [tabBarController.view setAlpha:0.0];
        [self.preMiniView release];
        self.preMiniView = nil;
        NSLog(@"applicationDidEnterBackground iphone"); 
    }

    - (void)initApp:(NSTimer *)timer
    {
        if (self.preMiniView)
        {
            [NSTimer scheduledTimerWithTimeInterval:0.5
                                             target:self     
                                           selector:@selector(removePrev:)
                                           userInfo:nil
                                            repeats:NO];
            [window insertSubview:tabBarController.view atIndex:0];
            [tabBarController.view setAlpha:1.0];
            [UIView beginAnimations:nil context:NULL];
            [UIView setAnimationDuration:.7];
            [self.preMiniView setAlpha:0.0];
            [UIView commitAnimations]; 
          }
    }
    - (void)removePrev:(NSTimer *)timer
    {
        [self.preMiniView removeFromSuperview];
    }

Secondly, I’m trying to present a pdf file with one of my UIViews when my app is hitting the method application:openURL:sourceApplication:annotation (used for opening a file from the email app). I get the correct file url but I’m not sure how to display the actual file in one of my custom UIView called PDFReaderViewController. It seems I can’t just use this code on the AppDelegate:

pdfController = [[PDFReaderViewController alloc] init];
[pdfController initFromName:fileName];

[[self navigationController] pushViewController:pdfController animated:YES];
[pdfController release];
pdfController = nil;

I get a warning: receiver ‘PDFReaderViewController’ is a forward class and corresponding @interface may not exist

Any idea how to display the new file using PDFReaderViewController from the AppDelegate?

I must be missing something basic here …. thanks for your help!

Answer 1

I want to point out that you are not properly following some memory management rules. The dot notation means you are accessing a property and that should be taking care of memory management for you and may be the reason for you EXC_BAD_ACCESS.

//You need to autorelease  the image view here
self.preMiniView = [[UIImageView alloc] initWithFrame:window.frame];
...
//Never release a property directly
[self.preMiniView release];
//This is the correct way to release the property
self.preMiniView = nil;

...

//This creates autoreleased image
UIImage *img = [UIImage imageNamed:@"preloadSm.jpg"];
//This will increment retain count
self.preMiniView.image = img;
//This is reason for EXC_BAD_ACCESS do not release you never retained it yourself
[img release];

The warning about a forward class reference means some where in a header file you probably have some code like @class PDFReaderViewController; and never include the the correct header in the implementation class.