"Next PDF Page" Button Doesn't Call -drawLayer. How to -setNeedsDisplay?

Question

- (void)viewDidLoad { [super viewDidLoad];

    page = 2;

    NSString *pathToPdfDoc = [[NSBundle mainBundle] pathForResource:@"2010_07" ofType:@"pdf"];
    NSURL *pdfUrl = [NSURL fileURLWithPath:pathToPdfDoc];

    myDocumentRef = CGPDFDocumentCreateWithURL((CFURLRef)pdfUrl);

    CGRect pageRect = CGRectIntegral(CGPDFPageGetBoxRect(CGPDFDocumentGetPage(myDocumentRef, page), kCGPDFCropBox));

    CATiledLayer *tiledLayer = [CATiledLayer layer];
    tiledLayer.delegate = self;
    tiledLayer.tileSize = CGSizeMake(593.0, 370.0);
    tiledLayer.levelsOfDetail = 6;
    tiledLayer.levelsOfDetailBias = 2;
    tiledLayer.frame = pageRect;

    myContentView = [[UIView alloc] initWithFrame:pageRect];
    [myContentView.layer addSublayer:tiledLayer];

    CGRect viewFrame = CGRectMake(0.0, 0.0, 480.0, 300.0);
    viewFrame.origin = CGPointZero;
    UIScrollView *scrollView = [[UIScrollView alloc] initWithFrame:viewFrame];
    scrollView.delegate = self;
    scrollView.contentSize = pageRect.size;
    scrollView.maximumZoomScale = 2;
    scrollView.minimumZoomScale = 0.8094;
    scrollView.zoomScale = 0.8094;
    [scrollView addSubview:myContentView];

    UIButton *nextButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    [nextButton addTarget:self action:@selector(nextPage)
     forControlEvents:UIControlEventTouchUpInside];
    [nextButton setTitle:@"Next" forState:UIControlStateNormal];
    nextButton.frame = CGRectMake(425.0, 255.0, 50.0, 20.0);//425,275,50,20
    nextButton.alpha = 0.8;

    [self.view addSubview:scrollView];
    [self.view addSubview:nextButton];
}

- (void) nextPage
{
    NSLog(@"Next Page");
    page = 3;
    [self setNeedsDisplay];
    BOOL displayNeeded = [self needsDisplay];
    if(displayNeeded)
        NSLog(@"Display Needed");
    [self displayIfNeeded];
}

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView
{
    return myContentView;
}

- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx
{   
    CGContextSetRGBFillColor(ctx, 1.0, 1.0, 1.0, 1.0);
    CGContextFillRect(ctx, CGContextGetClipBoundingBox(ctx));
    CGContextTranslateCTM(ctx, 0.0, layer.bounds.size.height);
    CGContextScaleCTM(ctx, 1.0, -1.0);
    CGContextConcatCTM(ctx, CGPDFPageGetDrawingTransform(CGPDFDocumentGetPage(myDocumentRef, page), kCGPDFCropBox, layer.bounds, 0, true));
    CGContextDrawPDFPage(ctx, CGPDFDocumentGetPage(myDocumentRef, page));
}

@end

I have code here that displays a PDF page. There's a button that supposedly will draw the next page of the PDF document. I have tried to -setNeedsDisplay on almost everything but it never seemed to update. I'm not trying to draw it offscreen so it should update correctly, right?

I don't have much understanding on Core Animation so I'm quite lost. My understanding is that -drawLayer will only draw when it needs to after you -setNeedsDisplay. Is this why nothing updates? Can you force it to draw?