Question

the problem I’ve met today is with my subclass of UIPageControl. When I initialize it, the frame (specifically the origin) and image of dots stays default, which is the problem, since I want it to change right after initialization. However, when I move with scrollView (as in “touch and move”) after initialization, they (the dots) somehow jump to the right position with correct images.

What could be the problem?

Code:

CustomPageControl.m

- (id) initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];

    activeImage = [UIImage imageNamed:@"doton.png"];
    inactiveImage = [UIImage imageNamed:@"dotoff.png"];

    return self;
}

- (void) updateDots
{
    for (int i = 0; i < [self.subviews count]; i++)
    {
        UIImageView *dot = [self.subviews objectAtIndex:i];
        if (i == self.currentPage) dot.image = activeImage;
        else dot.image = inactiveImage;
        [dot setFrame:CGRectMake(i * 13.5, 1.5, 17, 17)];
    }    
}

- (void)setCurrentPage:(NSInteger)currentPage
{
    [super setCurrentPage:currentPage];
    [self updateDots];
}

@end

ChoosingView.m – init part

scrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, 160, 300)];
[scrollView setBackgroundColor:[UIColor clearColor]];
[scrollView setDelaysContentTouches:NO];
[scrollView setCanCancelContentTouches:YES];
[scrollView setClipsToBounds:NO];
[scrollView setScrollEnabled:YES];
[scrollView setPagingEnabled:YES];
[scrollView setShowsHorizontalScrollIndicator:NO];
[scrollView setShowsVerticalScrollIndicator:NO];

pageControl = [[CustomPageControl alloc] initWithFrame:CGRectMake(200, 300, 80, 20)];
[pageControl setBackgroundColor:[UIColor clearColor]];
pageControl.numberOfPages = 6;
[pageControl setCurrentPage:0];

the last line is when I would expect the UIPageControl to refresh, however that does not happen.

Answer 1

Does this happen with the standard UIPageControl implementation?

Your problem states that your objects subViews (eg the UIImageViews) rects/size are not initialising to your desired size/position.
I implemented this code in my project with a nib rather than programmatically and I needed to call -(void)updateDots to set it as its initial condition was the standard dots..

I dont see how the UIScrollView has any bearing impact on this unless somehow its linked to your -(void)updateDots function (E.g. your setting the currentIndex of your custom page control). You state, “However, when I move with scrollView (as in “touch and move”) after initialization, they (the dots) somehow jump to the right position with correct images.”
Because they “jump to the right position with correct images” it means that your -(void)updateDots function must be getting called. I dont see any other explanation.

Also your iteration loop assumes that all the UIViews in your .subViews array are UIImageViews, although fairly safe to assume this, I would check to see if the UIView is a UIImageView with reflection.