UIScrollView phantom subviews

Question

I am loading a view from a nib file using:

NSArray *nibViews = [[NSBundle mainBundle] loadNibNamed:@"AnalysisView" owner:self options:nil];
AnalysisView *gridView = [nibViews objectAtIndex: 0];

The nib contains a scrollview called gridScrollView and in the AnalysisView implementation file I have a method which adds views as subviews to the scrollview:

for (NSInteger i = [results count] -1; i >= 0; i--) 
{
    Result *result = [results objectAtIndex:i];
    [self loadResult: result];
}

- (void) loadResult: (Result *) result
{
    NSArray *nibViews = [[NSBundle mainBundle] loadNibNamed:@"GridView" owner:self options:nil];
    GridView *gridView = [nibViews objectAtIndex: 0];
    gridView.tag = self.graphCount;

    CGRect gridFrame = gridView.frame;

    CGFloat yOffset = gridFrame.size.height * self.graphCount;
    gridView.frame = CGRectMake(0, yOffset, gridFrame.size.width, gridFrame.size.height);

    [self.gridScrollView addSubview: gridView];
    self.gridScrollView.contentSize = CGSizeMake(self.gridScrollView.frame.size.width, (yOffset + gridFrame.size.height));

    self.graphCount++;
}

I have set the scrollviews delegate to be AnalysisView and hooked up the did end decelaring method

-(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
      NSLog(@"%d", [scrollView.subviews count]);
}

When the scrollViewDidEndDecelerating method fires it reports that the number of subviews is 5. 3 of these subviews are GridViews which I expect. However there are 2 UIImageViews which I have no idea why they are there.

This is an issue because I intend on retrieving the views with viewWithTag in the scrollViewDidEndDecelerating method and calling a method on the view, however whenever I try to retrieve a view with a tag of 0 I will retrieve one of the UIImageView's and this causes my app to crash because the method cannot be called on an image view.

I know a way round this is to store my GridViews in a seperate instance array and reference them from there. But I'm curious to know what the 2 UIImageViews are and how they got there.

Answer 1

UIScrollView by default contains 2 UIImageViews as subviews for scroll indicators. Although I can't find anything specific about scroll indicators implementation in docs, those imageviews are present in class declaration (see UIScrollView.h header):

UIKIT_CLASS_AVAILABLE(2_0) @interface UIScrollView : UIView <NSCoding> {
    ...
    UIImageView* _verticalScrollIndicator;
    UIImageView* _horizontalScrollIndicator;

You can also start assigning tags not from 0, but from some positive number - that way avoiding collision with standard subviews