UiAlertView with UIProgressView for copying files locally
===

I've been trying to get this working for a day now and I'm still failing. I want to copy a number of files into the Documents folder of my app from the bundle when the app is installed,  but this makes the user wait for a long time with the app showing the splash screen. 

So I thought I'd make an initial UIAlertView with a UIProgressView as a subview that gets updated every time a file is copied into the documents folder. However the alert shows and the  progress bar never gets updated. My logic was:

- Set up the UIProgressView and UIAlertView as instance variables of my ViewController.
- In ViewDidLoad, present the alert and set the delegate
- In `- (void)didPresentAlertView:(UIAlertView *)alertView` perform a for loop that copies the files and updates the UI. the code was : 

        - (void)didPresentAlertView:(UIAlertView *)alertView{
            NSString *src, *path;
            src = // path to the Bundle folder where the docs are stored //
            NSArray *docs = [[NSFileManager defaultManager]contentsOfDirectoryAtPath:src error:nil];
        
            float total = (float)[docs count];
            float index = 1;
        
            for (NSString *filename in docs){
                path = [src stringByAppendingPathComponent:filename];
                if ([[NSFileManager defaultManager]fileExistsAtPath:path]) {
                    ... // Copy files into documents folder
                    [self performSelectorOnMainThread:@selector(changeUI:) withObject:[NSNumber numberWithFloat:index/total] waitUntilDone:YES];                
                    index++;
                }
            }
        [alertView dismissWithClickedButtonIndex:-1 animated:YES];
        }

And the code for ChangeUI is 

    - (void) changeUI: (NSNumber*)value{
        NSLog(@"change ui %f", value.floatValue);
        [progressBar setProgress:value.floatValue];
    }

However this just updates the UI from 0 to 1, although the NSLog prints all the intermediate values. Does anyone here know what I'm doing wrong?

Thanks in advance.