xcode IOS：具有无限分页视图的 UIScrollView

IOS: UIScrollView with an infinite paging view

提问by cyclingIsBetter

I have this code for a scrollview to showe 3 images:

我有一个滚动视图的代码来显示 3 个图像：

const CGFloat kScrollObjHeight = 150.0;
const CGFloat kScrollObjWidth = 320.0;
const NSUInteger kNumImages = 3;


- (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)];

}

- (void)viewDidLoad
{
self.view.backgroundColor = [UIColor viewFlipsideBackgroundColor];

// 1. setup the scrollview for multiple images and add it to the view controller
//
// note: the following can be done in Interface Builder, but we show this in code for clarity
[scrollView1 setBackgroundColor:[UIColor blackColor]];
[scrollView1 setCanCancelContentTouches:NO];
scrollView1.indicatorStyle = UIScrollViewIndicatorStyleWhite;
scrollView1.clipsToBounds = YES;        // default is NO, we want to restrict drawing within our scrollview
scrollView1.scrollEnabled = YES;

// pagingEnabled property default is NO, if set the scroller will stop or snap at each photo
// if you want free-flowing scroll, don't set this property.
scrollView1.pagingEnabled = YES;
scrollView2.pagingEnabled = YES;
scrollView3.pagingEnabled = YES;

// load all the images from our bundle and add them to the scroll view
NSUInteger i;
for (i = 1; i <= kNumImages; i++)
{
    NSString *imageName = [NSString stringWithFormat:@"image%d.jpg", i];
    UIImage *image = [UIImage imageNamed:imageName];
    UIImageView *imageView = [[UIImageView alloc] initWithImage:image];

    // setup each frame to a default height and width, it will be properly placed when we call "updateScrollList"
    CGRect rect = imageView.frame;
    rect.size.height = kScrollObjHeight;
    rect.size.width = kScrollObjWidth;
    imageView.frame = rect;
    imageView.tag = i;  // tag our images for later use when we place them in serial fashion
    [scrollView1 addSubview:imageView];
    //[scrollView2 addSubview:imageView];
    //[scrollView3 addSubview:imageView];
    [imageView release];
}

[self layoutScrollImages];  // now place the photos in serial layout within the scrollview

}

But now I want to do a scrollview that when is in last image show me after the first image of scroll view and the same thing when I have the first image if I go back, it must show the last image; so I want create a paging loop.

但是现在我想做一个滚动视图，当在最后一个图像中时，在滚动视图的第一张图像之后显示我，如果我回去，当我有第一张图像时，它必须显示最后一张图像；所以我想创建一个分页循环。

回答by Tommy

The basic idea is to set yourself as a UIScrollViewDelegate and apply some modulo arithmetic to the scroll position in order to wrap it around.

基本思想是将自己设置为 UIScrollViewDelegate 并对滚动位置应用一些模运算以将其环绕。

There are two basic variations on the idea. Suppose your images are A, B, C, so you currently have them within the scrollview ordered as ABC.

这个想法有两个基本的变化。假设您的图像是 A、B、C，因此您当前将它们放在按 ABC 排序的滚动视图中。

In the more logically pleasing solution — especially if you had lots and lots of images — you watch the scroll position and as soon as it gets to a position where the view is being pushed rightward and C has left the screen, you reorder the images as CAB and shift the current scroll position one spot to the right so that the move is invisible to the user. To put that another way, the scroll position is restrained to an area of two screens, centred on the middle of B (so, you get all of B and half a screen either side). Whenever you wrap it from somewhere on the left to somewhere on the right you shift all your image views one place to the right. And vice versa.

在更合乎逻辑的解决方案中——特别是如果你有很多很多图像——你观察滚动位置，一旦它到达视图被向右推并且 C 离开屏幕的位置，你将图像重新排序为CAB 并将当前滚动位置向右移动一位，以便用户看不到移动。换句话说，滚动位置被限制在两个屏幕的区域内，以 B 的中间为中心（因此，您将获得所有 B 和两侧的半个屏幕）。每当您将其从左侧某处包装到右侧某处时，您会将所有图像视图向右移动一个位置。反之亦然。

In the slightly easier to implement variation, instead of creating a scroll view with images arranged ABC, arrange then as CABCA. Then apply the same wrap around logic but to a central area of four screens and don't do any view reshuffling.

在稍微更容易实现的变化中，不是创建图像排列为 ABC 的滚动视图，而是排列为 CABCA。然后应用相同的环绕逻辑，但应用于四个屏幕的中心区域，并且不进行任何视图重排。

Make sure you use just setContentOffset:(or the dot notation, as in scrollView.contentOffset =) as a setter. setContentOffset:animated:will negate velocity.

确保您只使用setContentOffset:（或点符号，如scrollView.contentOffset =）作为 setter。setContentOffset:animated:将否定速度。