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我正在关注如何使用 UIScrollView 滚动和缩放内容的“使用 UIScrollView 进行分页”部分，并将4 个图像加载到数组中。我应该提到我正在将它加载到 UITabController 中，它是情节提要中的第一个视图控制器。

由于某种原因，视图加载时会出现两个问题：

一，页面控件不响应来自 UIScrollView 的更新（点根本不移动，而是用正确的页数计算）。

二，只有前两个页面加载，这让我认为 loadVisiblePages 方法不起作用。

从 View Controller 的 First Responder 连接起来的是一个 page control 到 pageControl 和一个 Scroll View 到 scrollView 和 view 到 View （默认），最后是关系 segue。

更新：我刚刚发现了关于这个问题的一些有趣的东西。如果我转到第 3 页（数组中的 3 个图像），我看不到图像。但是如果我切换选项卡，页面控件和图像都会正确显示。

标题：

#import <UIKit/UIKit.h>

@interface TutorialViewController : UIViewController <UIScrollViewDelegate>

@property (nonatomic, strong) IBOutlet UIScrollView *scrollView;
@property (nonatomic, strong) IBOutlet UIPageControl *pageControl;

@end

实施：

#import "TutorialViewController.h"

@interface TutorialViewController ()
@property (nonatomic, strong) NSArray *pageImages;
@property (nonatomic, strong) NSMutableArray *pageViews;

- (void)loadVisiblePages;
- (void)loadPage:(NSInteger)page;
- (void)purgePage:(NSInteger)page;
@end

@implementation TutorialViewController

@synthesize scrollView = _scrollView;
@synthesize pageControl = _pageControl;

@synthesize pageImages = _pageImages;
@synthesize pageViews = _pageViews;

- (void)loadPage:(NSInteger)page {
    if (page < 0 || page >= self.pageImages.count) {
        // If it's outside the range of what you have to display, then do nothing
        return;
    }

    // 1
    UIView *pageView = [self.pageViews objectAtIndex:page];
    if ((NSNull*)pageView == [NSNull null]) {
        // 2
        CGRect frame = self.scrollView.bounds;
        frame.origin.x = frame.size.width * page;
        frame.origin.y = 0.0f;

        // 3
        UIImageView *newPageView = [[UIImageView alloc] initWithImage:[self.pageImages objectAtIndex:page]];
        newPageView.contentMode = UIViewContentModeScaleAspectFit;
        newPageView.frame = frame;
        [self.scrollView addSubview:newPageView];
        // 4
        [self.pageViews replaceObjectAtIndex:page withObject:newPageView];
    }
}

- (void)purgePage:(NSInteger)page {
    if (page < 0 || page >= self.pageImages.count) {
        // If it's outside the range of what you have to display, then do nothing
        return;
    }

    // Remove a page from the scroll view and reset the container array
    UIView *pageView = [self.pageViews objectAtIndex:page];
    if ((NSNull*)pageView != [NSNull null]) {
        [pageView removeFromSuperview];
        [self.pageViews replaceObjectAtIndex:page withObject:[NSNull null]];
    }
}

- (void)loadVisiblePages {
    // First, determine which page is currently visible
    CGFloat pageWidth = self.scrollView.frame.size.width;
    NSInteger page = (NSInteger)floor((self.scrollView.contentOffset.x * 2.0f + pageWidth) / (pageWidth * 2.0f));

    // Update the page control
    self.pageControl.currentPage = page;

    // Work out which pages you want to load
    NSInteger firstPage = page - 1;
    NSInteger lastPage = page + 1;

    // Purge anything before the first page
    for (NSInteger i=0; i<firstPage; i++) {
        [self purgePage:i];
    }

    // Load pages in our range
    for (NSInteger i=firstPage; i<=lastPage; i++) {
        [self loadPage:i];
    }

    // Purge anything after the last page
    for (NSInteger i=lastPage+1; i<self.pageImages.count; i++) {
        [self purgePage:i];
    }
}

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    // Load the pages that are now on screen
    [self loadVisiblePages];
}

- (void)viewDidLoad {
    [super viewDidLoad];

    // 1
    self.pageImages = [NSArray arrayWithObjects:
                       [UIImage imageNamed:@"640x960 tutorial_1.png"],
                       [UIImage imageNamed:@"640x960 tutorial_2.png"],
                       [UIImage imageNamed:@"640x960 tutorial_3.png"],
                       [UIImage imageNamed:@"640x960 tutorial_4.png"],
                       nil];

    NSInteger pageCount = self.pageImages.count;

    // 2
    self.pageControl.currentPage = 0;
    self.pageControl.numberOfPages = pageCount;

    // 3
    self.pageViews = [[NSMutableArray alloc] init];
    for (NSInteger i = 0; i < pageCount; ++i) {
        [self.pageViews addObject:[NSNull null]];
    }
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];

    // 4
    CGSize pagesScrollViewSize = self.scrollView.frame.size;
    self.scrollView.contentSize = CGSizeMake(pagesScrollViewSize.width * self.pageImages.count, pagesScrollViewSize.height);

    // 5
    [self loadVisiblePages];
}

@end
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1 回答 1

2

我终于弄明白了。

用户错误。我将 View 而不是我的 ViewController 链接为故事板中的委托。

感谢您的观看，我希望这对其他人有所帮助，这样他们就不必在两天内拔掉头发！

于 2012-12-12T07:51:50.363 回答