UIPageViewController / TextKit在分页上回流文本

Question

我正在开发一个由TextKit支持的多页面阅读应用程序，它基于WWDC 2013的“高级文本布局和文本工具包效果”会话（但是有一些代码是从不完整的示例重建的）。基本结构是您预先计算文本所需的页数，然后为每个页面创建一个NSTextContainer并将其添加到NSLayoutManager。每当UIPageViewController请求下一页或上一页时，您创建一个新的UITextView并通过从NLayoutManger的NSTextContainers数组中选择正确的一个来设置其后备文本容器。

不幸的是，我遇到了一个问题，即文本在第一页和第一次回页到任何给定页面时都被重排。这是它的样子：

这不是最明显的效果（如果你错过了它，在回调时注意屏幕的顶部），但它有点迷惑，我想尽可能消除它。鉴于文本容器应该预先计算，我不明白它为什么要回流文本，或者如何防止它。有谁知道问题是什么？

编辑：添加代码示例。

@interface ReaderViewController () <UIPageViewControllerDataSource>

@property (nonatomic, assign) NSUInteger numberOfPages;

@property (nonatomic, retain) UIPageViewController *pageViewController;
@property (nonatomic, retain) NSTextStorage *currentDocument;
@property (nonatomic, retain) NSLayoutManager *layoutManager;

@end

@implementation ReaderViewController

- (instancetype)initWithDocument:(NSTextStorage *)document {
  if ((self = [super init])) {
    _currentDocument = document;
  }
  return self;
}

- (void)viewDidLoad
{
  [super viewDidLoad];

  _layoutManager = [[NSLayoutManager alloc] init];
  [self.layoutManager setTextStorage:self.currentDocument];
  self.layoutManager.delegate = self;

  _pageViewController = [[UIPageViewController alloc] initWithTransitionStyle:UIPageViewControllerTransitionStyleScroll
                                                        navigationOrientation:UIPageViewControllerNavigationOrientationHorizontal
                                                                      options:nil];
  self.pageViewController.view.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
  self.pageViewController.dataSource = self;
  [self addChildViewController:self.pageViewController];
  [self.view addSubview:self.pageViewController.view];

  // the numberOfPages accessor lazily calculates the number of pages needed to contain the document
  for (int i = 0; i < self.numberOfPages; ++i) {
    NSTextContainer *container = [[NSTextContainer alloc] init];
    container.size = [self _textFrame].size;
    [self.layoutManager addTextContainer:container];
  }

  [self.pageViewController setViewControllers:@[[self viewControllerForPageNumber:0]] direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:nil];
}

- (UIViewController *)viewControllerForPageNumber:(NSUInteger)pageNumber {
  if (pageNumber >= self.numberOfPages) {
    return nil;
  }

  // SinglePageViewController is a lightweight view controller that has a UITextView and a page number
  SinglePageViewController *vc = [[SinglePageViewController alloc] init];

  UITextView *textView = [[UITextView alloc] initWithFrame:[self _textFrame] textContainer:[self.layoutManager.textContainers objectAtIndex:pageNumber]];
  textView.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
  textView.scrollEnabled = NO;
  textView.editable = NO;
  [textView setFont:[UIFont fontWithName:@"IowanOldStyle-Roman" size:20.f]];
  [vc.view addSubview:textView];

  vc.textView = textView;
  vc.pageNumber = pageNumber;

  return vc;
}

#pragma mark - UIPageViewControllerDataSource

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController {
  NSUInteger currentPage = [(SinglePageViewController *)viewController pageNumber];
  if (currentPage >= self.numberOfPages) {
    return nil;
  }

  return [self viewControllerForPageNumber:currentPage + 1];
}

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController {
  NSUInteger currentPage = [(SinglePageViewController *)viewController pageNumber];
  if (currentPage == 0) {
    return nil;
  }

  return [self viewControllerForPageNumber:currentPage - 1];
}

#pragma mark - Private

- (CGRect)_textFrame {
  return CGRectInset(self.view.bounds, 5., 0.);
}

@end

Answer 1

我遇到了同样的问题。我的解决方案是在scrollEnabled之后addSubview强制textContainer重新计算大小。见下面的代码：

vc.view.addSubview(textView)
textView.scrollEnabled = false;

<强>更新即可。最后，我想我找到了正确答案......我们需要在didChangeGeometryFromSize回调中重置容器大小。如果不是这样，请纠正我：）

func layoutManager(layoutManager: NSLayoutManager, 
                   textContainer: NSTextContainer, 
                   didChangeGeometryFromSize oldSize: CGSize) {

    textContainer.size = self.textFrame().size;
    println(textContainer.size.width)
    println(textContainer.size.height)
}

Answer 2

Try to set automaticallyAdjustsScrollViewInsets of your view controller to NO.