Question

I got this code from the apple sample project scrolling:

@synthesize scrollView1, scrollView2;

const CGFloat kScrollObjHeight  = 467.0;
const CGFloat kScrollObjWidth   = 320.0;
const NSUInteger kNumImages     = 6;


- (void)layoutScrollImages
{
    UIImageView *view = nil;
    NSArray *subviews = [scrollView1 subviews];


    // reposition all image subviews in a horizontal serial fashion
    CGFloat curXLoc = 0;
    for (view in subviews)
    {
        if ([view isKindOfClass:[UIImageView class]] && view.tag > 0)
        {
            CGRect frame = view.frame;
            frame.origin = CGPointMake(curXLoc, 0);
            view.frame = frame;

            curXLoc += (kScrollObjWidth);
        }
    }

    // set the content size so it can be scrollable
    [scrollView1 setContentSize:CGSizeMake((kNumImages * kScrollObjWidth), [scrollView1 bounds].size.height)];
}

I tried to modify this to load subviews instead of images but it doesnt work. I think I’m somehow replacing the views instead of adding them? I need to load the views from separate xib files, and scroll left to right through the xib’s (they each contain a panel of buttons leading to different levels in my game). So what am I doing wrong? Why doesnt this work? It only ever shows the second panel and whenever i push a button it crashes with a SIGABRT.

#import "LevelSelectButtons.h"

@implementation LevelSelectButtons
@synthesize levelScroll;

const int kScrollObjHeight = 400;
const int kScrollObjWidth = 320;
const NSUInteger kNumCategories = 5;

- (void)layoutScrollScreens {
    UIImageView *view = nil;
    NSArray *subviews = [levelScroll subviews];

    // reposition all image subviews in a horizontal serial fashion
    CGFloat curXLoc = 0;
    for (view in subviews) {
        if ([view isKindOfClass:[UIImageView class]] && view.tag > 0) {
            CGRect frame = view.frame;
            frame.origin = CGPointMake(curXLoc, 0);
            view.frame = frame;

            curXLoc += (kScrollObjWidth);
        }
    }

    // set the content size so it can be scrollable
    [levelScroll setContentSize:CGSizeMake((kNumCategories * kScrollObjWidth), [levelScroll bounds].size.height)];
}

- (void)viewDidLoad {
    [levelScroll setScrollEnabled:YES];
    CGFloat width = 640; //kScrollObjWidth*kNumCategories;
    CGFloat height = 400;
    [levelScroll setContentSize:CGSizeMake(width, height)];
    [self.view addSubview:levelScroll];
    levelScroll.pagingEnabled = YES;
    levelScroll.indicatorStyle = UIScrollViewIndicatorStyleWhite;

    levelScroll.pagingEnabled = YES;

    /// LEVELS 1 ///
    NSUInteger viewNum = 0;
    CGRect catViewFrame = CGRectMake(0, 0, kScrollObjWidth, kScrollObjHeight);
    UIView *levels1view = [[UIView alloc] initWithFrame:catViewFrame];

    NSArray *array1 = [[NSBundle  mainBundle] loadNibNamed:@"Levels1" owner:self options:nil];
    levels1view = [array1 objectAtIndex:0];
    levels1view.tag = viewNum;

    [self.levelScroll addSubview:levels1view];


    /// LEVELS 2 ///
    viewNum = 1;
    catViewFrame = CGRectMake(320, 0, kScrollObjWidth, kScrollObjHeight);
    UIView *levels2view = [[UIView alloc] initWithFrame:catViewFrame];
    NSArray * array2= [[NSBundle mainBundle] loadNibNamed:@"Levels2" owner:self options:nil];
    levels2view = [array2 objectAtIndex:0];
    levels2view.tag = viewNum;

    [self.levelScroll addSubview:levels2view];

    [self layoutScrollScreens];
    [super viewDidLoad];
}

This is the line where the SIGABRT appears:

int retVal = UIApplicationMain(argc, argv, nil, nil);

Answer 1

This is to explain why only levels2view is shown.

/// LEVELS 2 ///
viewNum = 1;
catViewFrame = CGRectMake(320, 0, kScrollObjWidth, kScrollObjHeight);
UIView *levels2view = [[UIView alloc] initWithFrame:catViewFrame];

If you look here, you’re creating a new view with the desired frame where you want your levels2view to be positioned. But,

NSArray * array2= [[NSBundle mainBundle] loadNibNamed:@"Levels2" owner:self options:nil];
levels2view = [array2 objectAtIndex:0];
levels2view.tag = viewNum;

[self.levelScroll addSubview:levels2view];

Here you’re reassigning the variable to a new view and thus losing the reference to the view you created resulting in a memory leak. That aside, this view doesn’t have its frame set. This will default to origin being at CGPointZero. And since you do the same thing with levels1view, you end up positioning levels2view on top of levels1view when you add them to the scroll view when you add them in that order.

To remedy this,

viewNum = 1;
catViewFrame = CGRectMake(320, 0, kScrollObjWidth, kScrollObjHeight);

NSArray * array2= [[NSBundle mainBundle] loadNibNamed:@"Levels2" owner:self options:nil];
UIView * levels2view = [array2 objectAtIndex:0];
levels2view.frame = catViewFrame;
levels2view.tag = viewNum;

[self.levelScroll addSubview:levels2view];