1

我的情况：

我有来自 Apple 的原始页面控制应用程序。我想在 UIScrollView 底部的页面控件的右侧修改应用程序的启动？默认情况下，启动时 - 它位于左侧的第一页上。例如，我有 7 页。所以，我希望第一页出现在第 7 页的最后一页和第 6 页的第二页，依此类推。简而言之，与默认相反。

我知道必须有一个代码可以做到这一点。我不确定它是什么。请帮忙。谢谢！

以下是来自 Apple 的 Page Control 应用程序的描述：

页面控件

此应用程序演示了使用 UIScrollView 的分页功能来使用水平滚动作为在不同内容页面之间导航的机制。每个页面都由其自己的视图控制器管理，该控制器仅在需要时才加载。UIPageControl 显示在窗口底部，作为在页面之间移动的替代界面

AppDelegate.m 中的代码

#import "AppDelegate.h"
#import "MyViewController.h"

static NSUInteger kNumberOfPages = 7;

@interface AppDelegate (PrivateMethods)

- (void)loadScrollViewWithPage:(int)page;
- (void)scrollViewDidScroll:(UIScrollView *)sender;

@end

@implementation AppDelegate

@synthesize window, scrollView, pageControl, viewControllers;

- (void)dealloc {
    [viewControllers release];
    [scrollView release];
    [pageControl release];
    [window release];
    [super dealloc];
}

- (void)applicationDidFinishLaunching:(UIApplication *)application {
    // view controllers are created lazily
    // in the meantime, load the array with placeholders which will be replaced on demand
    NSMutableArray *controllers = [[NSMutableArray alloc] init];
    for (unsigned i = 0; i < kNumberOfPages; i++) {
        [controllers addObject:[NSNull null]];
    }
    self.viewControllers = controllers;
    [controllers release];

    // a page is the width of the scroll view
    scrollView.pagingEnabled = YES;
    scrollView.contentSize = CGSizeMake(scrollView.frame.size.width * kNumberOfPages, scrollView.frame.size.height);
    scrollView.showsHorizontalScrollIndicator = NO;
    scrollView.showsVerticalScrollIndicator = NO;
    scrollView.scrollsToTop = NO;
    scrollView.delegate = self;

    pageControl.numberOfPages = kNumberOfPages;
    pageControl.currentPage = 0;

    // pages are created on demand
    // load the visible page
    // load the page on either side to avoid flashes when the user starts scrolling
    [self loadScrollViewWithPage:0];
    [self loadScrollViewWithPage:1];
}

- (void)loadScrollViewWithPage:(int)page {
    if (page < 0) return;
    if (page >= kNumberOfPages) return;

    // replace the placeholder if necessary
    MyViewController *controller = [viewControllers objectAtIndex:page];
    if ((NSNull *)controller == [NSNull null]) {
        controller = [[MyViewController alloc] initWithPageNumber:page];
        [viewControllers replaceObjectAtIndex:page withObject:controller];
        [controller release];
    }

    // add the controller's view to the scroll view
    if (nil == controller.view.superview) {
        CGRect frame = scrollView.frame;
        frame.origin.x = frame.size.width * page;
        frame.origin.y = 0;
        controller.view.frame = frame;
        [scrollView addSubview:controller.view];
    }
}

- (void)scrollViewDidScroll:(UIScrollView *)sender {
    // We don't want a "feedback loop" between the UIPageControl and the scroll delegate in
    // which a scroll event generated from the user hitting the page control triggers updates from
    // the delegate method. We use a boolean to disable the delegate logic when the page control is used.
    if (pageControlUsed) {
        // do nothing - the scroll was initiated from the page control, not the user dragging
        return;
    }
    // Switch the indicator when more than 50% of the previous/next page is visible
    CGFloat pageWidth = scrollView.frame.size.width;
    int page = floor((scrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1;
    pageControl.currentPage = page;

    // load the visible page and the page on either side of it (to avoid flashes when the user starts scrolling)
    [self loadScrollViewWithPage:page - 1];
    [self loadScrollViewWithPage:page];
    [self loadScrollViewWithPage:page + 1];

    // A possible optimization would be to unload the views+controllers which are no longer visible
}

// At the end of scroll animation, reset the boolean used when scrolls originate from the UIPageControl
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
    pageControlUsed = NO;
}

- (IBAction)changePage:(id)sender {
    int page = pageControl.currentPage;
    // load the visible page and the page on either side of it (to avoid flashes when the user starts scrolling)
    [self loadScrollViewWithPage:page - 1];
    [self loadScrollViewWithPage:page];
    [self loadScrollViewWithPage:page + 1];
    // update the scroll view to the appropriate page
    CGRect frame = scrollView.frame;
    frame.origin.x = frame.size.width * page;
    frame.origin.y = 0;
    [scrollView scrollRectToVisible:frame animated:YES];
    // Set the boolean used when scrolls originate from the UIPageControl. See scrollViewDidScroll: above.
    pageControlUsed = YES;
}

@end
4

2 回答 2

2

好吧，您可以将滚动视图偏移量设置为最后一页，然后它将从最后一页开始，您必须向右滚动而不是向左滚动...使用 UIScrollViews - (void)setContentOffset:(CGPoint) contentOffset 动画：（BOOL）动画方法。

于 2009-08-19T17:44:06.770 回答
2

从 Apple 获取 PageControl 示例，下面是执行此操作的代码。我对其进行了测试，它工作正常，除了在您将应用程序从初始点启动到最后一个点时注意到页面控件的跳转，但我不知道如何解决这个问题。如果这对你不起作用，请告诉我。

- (void)applicationDidFinishLaunching:(UIApplication *)application {
    // view controllers are created lazily
    // in the meantime, load the array with placeholders which will be replaced on demand
    NSMutableArray *controllers = [[NSMutableArray alloc] init];
    for (unsigned i = 0; i < kNumberOfPages; i++) {
        [controllers addObject:[NSNull null]];
    }
    self.viewControllers = controllers;
    [controllers release];

    // a page is the width of the scroll view
    scrollView.pagingEnabled = YES;
    scrollView.contentSize = CGSizeMake(scrollView.frame.size.width * kNumberOfPages, scrollView.frame.size.height);
    scrollView.showsHorizontalScrollIndicator = NO;
    scrollView.showsVerticalScrollIndicator = NO;
    scrollView.scrollsToTop = NO;
    scrollView.delegate = self;

    // First, set the number of pages
    pageControl.numberOfPages = kNumberOfPages;
    // Then, tell the page control that you're on the last page (numPages - 1, since we're 0-indexed)
    pageControl.currentPage = kNumberOfPages - 1;

    // Now, we have to tell the frame that we're at the end of the frame
    // So we set the content offset to be the last page
    scrollView.contentOffset = CGPointMake(scrollView.frame.size.width * (kNumberOfPages - 1), 0);

    // pages are created on demand
    // load the visible page
    // load the page on either side to avoid flashes when the user starts scrolling
    // [self loadScrollViewWithPage:0];
    // [self loadScrollViewWithPage:1];

    // Now, instead of loading the original page, we load the last two pages
    [self loadScrollViewWithPage:kNumberOfPages - 1];
    [self loadScrollViewWithPage:kNumberOfPages - 2];
}
于 2009-08-19T19:10:07.283 回答