Question

I have a UINavigationController in my application where I am pushing a view controller. On that viewcontroller, there is a preloader view that shows animation while the data is being downloaded and parsed in the background. Below the animation is a button that should redirect the user to some other view controller.

Now, I can accomplish this by popping the viewcontroller since the view I need to be directed to is the view the current view was pushed from. The problem here, however, is that the downloading, parsing, timer, etc.. everything keeps happening in the background.

The functionality I need is for the viewcontroller to completely stop working as soon as I pop the VC by clicking on the button.

Thanks in advance.

Answer 1

What are you using to run the background operations?

You can simplify background operations by subclassing NSOperation and using NSOperationQueue to run it. You just have to release NSOperationQueue and iOS will clean up for you automatically.

https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/NSOperation_class/Reference/Reference.html

https://developer.apple.com/library/ios/#documentation/Cocoa/Reference/NSOperationQueue_class/Reference/Reference.html

Here is an example.

@interface MyBackgroundOperation : NSOperation
@end

@implementation MyBackgroundOperation
- (id)init
{
    self = [super init];

    if(self != nil)
    {        
        // stuff that needs to be done at init
    }

    return self;
}

- (void)main
{
    @try
    {
        // run my background operations
    }
    @catch (NSException *e)
    {
        // catch the exception
    }
}

- (void)dealloc
{
    // clean up
    [super dealloc];
}
@end

Then you start the operation like this

NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];

MyBackgroundOperation *myOperation = [[MyBackgroundOperation alloc] init];
[operationQueue addOperation:myOperation];
[myOperation release];

[operationQueue release];

The OS will retain the operation until it’s finished so that releasing the view controller will not effect it. However, if you want to stop the operation after it’s already started you’re going to have to use a bit more fancy techniques, maybe notifications or KVO.