1 UIScrollView无限滚动
2
3 #import "ViewController.h"
4
5 #define kCount 8
6
7 @interface ViewController () <UIScrollViewDelegate>
8 {
9 UIImageView *_reusableView; // 循环利用的
10 UIImageView *_centerView; // 中间的
11 }
12 @property (weak, nonatomic) IBOutlet UIScrollView *scrollView;
13 @end
14
15 @implementation NJViewController
16
17 - (void)viewDidLoad
18 {
19 [super viewDidLoad];
20
21 CGFloat w = _scrollView.frame.size.width;
22 NSLog(@"%f",w);
23 CGFloat h = _scrollView.frame.size.height;
24 _scrollView.pagingEnabled = YES;
25 _scrollView.contentSize = CGSizeMake(w * 3, 0);
26 _scrollView.contentOffset = CGPointMake(w, 0);
27 _scrollView.showsHorizontalScrollIndicator = NO;
28
29 _centerView = [[UIImageView alloc] init];
30 _centerView.image = [UIImage imageNamed:@"00.jpg"];
31 _centerView.frame = CGRectMake(w, 0, w, h);
32 _centerView.tag = 0;
33 [_scrollView addSubview:_centerView];
34
35 _reusableView = [[UIImageView alloc] init];
36 _reusableView.frame = _scrollView.bounds;
37 }
38
39 - (void)scrollViewDidScroll:(UIScrollView *)scrollView
40 {
41 CGFloat offsetX = scrollView.contentOffset.x;
42 CGFloat w = scrollView.frame.size.width;
43 NSLog(@"offsetX = %f and _centerView.frame.origin.x = %f",offsetX,_centerView.frame.origin.x);
44 // 1.设置 循环利用view 的位置
45 CGRect f = _reusableView.frame;
46 int index = 0;
47 if (offsetX > _centerView.frame.origin.x) { // 显示在最右边
48 NSLog(@"scrollView.contentSize.width = %f",scrollView.contentSize.width);
49 f.origin.x = scrollView.contentSize.width - w;
50
51 index = _centerView.tag + 1;
52 if (index >= kCount) index = 0;
53 } else { // 显示在最左边
54 f.origin.x = 0;
55
56 index = _centerView.tag - 1;
57 if (index < 0) index = kCount - 1;
58 }
59 _reusableView.frame = f;
60 _reusableView.tag = index;
61 NSString *icon = [NSString stringWithFormat:@"0%d.jpg", index];
62 _reusableView.image = [UIImage imageNamed:icon];
63
64 // 2.显示了 最左 或者 最右 的图片
65 if (offsetX <= 0 || offsetX >= w * 2) {
66 // 2.1.交换 中间的 和 循环利用的
67 UIImageView *temp = _centerView;
68 _centerView = _reusableView;
69 _reusableView = temp;
70
71 // 2.2.设置显示位置
72 _centerView.frame = _reusableView.frame;
73 scrollView.contentOffset = CGPointMake(w, 0);
74
75 [_reusableView removeFromSuperview];
76 } else {
77 [_scrollView addSubview:_reusableView];
78 }
79 }
80 @end
