iPhone - 全屏 UIScrollView 向右启动，但重新定位在导航栏下方

Question

我目前正在尝试实现一个照片选择器，就像照片应用程序一样，但具有自定义图像源。对于“照片滚动”部分，我使用了 Apple PhotoScroller 示例代码并对其进行了修改。主要区别之一是它现在嵌入了导航 Controller (这是 photoPicker 自己的导航 Controller ，而不是应用程序的导航 Controller )，并带有导航栏。我的状态栏和导航栏是半透明的，并且我在 photoPicker 中使用的所有 View Controller 上设置了wantFullScreenLayout = YES。看起来效果几乎很好。 “概览” View (显示所有相册照片的缩略图的 View )确实是全屏的，我必须手动偏移它，以便缩略图首先显示在导航栏下方。然而，对于滚动部分有一个小故障。对于那些不了解 photoScroller 示例代码的人，它与带有 UIScrollView 属性 (pagingScrollView) 的自定义 UIViewController (PhotoViewController) 以及一组带有 UIView 和 NSInteger 索引属性的自定义 UIScrollView (ImageScrollView) 配合使用。然后将 ImageScrollView 实例作为 PhotoScroller 的 subview 添加/删除。

下面是一些相关代码:

PhotoViewController.h

@interface PhotoViewController : UIViewController <UIScrollViewDelegate> {
    UIScrollView *pagingScrollView;

    NSMutableSet *recycledPages;
    NSMutableSet *visiblePages;

    IBOutlet UIToolbar *toolbar;
    IBOutlet UIBarButtonItem *previousButtonItem;
    IBOutlet UIBarButtonItem *nextButtonItem;

    id<PhotoViewDataSource> dataSource;
}

@property(nonatomic, retain) UIScrollView *pagingScrollView;
@property(nonatomic, retain) NSMutableSet *recylcledPages;
@property(nonatomic, retain) NSMutableSet *visiblePages;

@property(nonatomic, retain) UIToolbar *toolbar;
@property(nonatomic, retain) UIBarButtonItem *previousButtonItem;
@property(nonatomic, retain) UIBarButtonItem *nextButtonItem;

@property(nonatomic, retain) id<PhotoViewDataSource> dataSource;

PhotoViewController.m

- (void)loadView 
{
    self.wantsFullScreenLayout = YES;

    // Configure the scrollView
    CGRect pagingScrollViewFrame = [self frameForPagingScrollView];
    pagingScrollView = [[UIScrollView alloc] initWithFrame:pagingScrollViewFrame];
    pagingScrollView.pagingEnabled = YES;
    pagingScrollView.backgroundColor = [UIColor redColor];
    pagingScrollView.showsVerticalScrollIndicator = NO;
    pagingScrollView.showsHorizontalScrollIndicator = NO;
    pagingScrollView.contentSize = CGSizeMake(pagingScrollViewFrame.size.width * [self.dataSource imageCount],
                                              pagingScrollViewFrame.size.height);
    //pagingScrollView.contentOffset = CGPointMake(0, 0);

    pagingScrollView.delegate = self;
    self.view = pagingScrollView;

    // TODO ? Prepare to tile content
    recycledPages = [[NSMutableSet alloc] init];
    visiblePages  = [[NSMutableSet alloc] init];
    [self processPages];
}


- (void)processPages {

    // Calculate which pages are visible
    CGRect visibleBounds = pagingScrollView.bounds;
    NSLog(@"PhotoViewController - processPages : frame = %@", NSStringFromCGRect(pagingScrollView.frame));
    NSLog(@"pagingScrollView bounds = %@", NSStringFromCGRect(pagingScrollView.bounds));
    NSLog(@"and contentSize = %@", NSStringFromCGSize(pagingScrollView.contentSize));

    int firstNeededPageIndex = floorf(CGRectGetMinX(visibleBounds) / CGRectGetWidth(visibleBounds));
    int lastNeededPageIndex  = floorf((CGRectGetMaxX(visibleBounds)-1) / CGRectGetWidth(visibleBounds));
    firstNeededPageIndex = MAX(firstNeededPageIndex, 0);
    lastNeededPageIndex  = MIN(lastNeededPageIndex, [dataSource imageCount] - 1);

    if (lastNeededPageIndex >= 0) {

        // Recycle no-longer-visible pages 
        for (ImageScrollView *page in visiblePages) {
            if (page.index < firstNeededPageIndex || page.index > lastNeededPageIndex) {
                [recycledPages addObject:page];
                [page removeFromSuperview];
            }
        }
        [visiblePages minusSet:recycledPages];

        // add missing pages
        for (int index = firstNeededPageIndex; index <= lastNeededPageIndex; index++) {
            if (![self isDisplayingPageForIndex:index]) {
                ImageScrollView *page = [self dequeueRecycledPage];
                if (page == nil) {
                    page = [[[ImageScrollView alloc] init] autorelease];
                }
                [self configurePage:page forIndex:index];
                NSLog(@"PhotoViewController - processPage 2 : bounds = %@", NSStringFromCGRect(pagingScrollView.bounds));
                [pagingScrollView addSubview:page];
                NSLog(@"PhotoViewController - processPage 3 : bounds = %@", NSStringFromCGRect(pagingScrollView.bounds));
                [visiblePages addObject:page];
            }
        }
    }
}

- (ImageScrollView *)dequeueRecycledPage {
    ImageScrollView *page = [recycledPages anyObject];
    if (page) {
        [[page retain] autorelease];
        [recycledPages removeObject:page];
    }
    return page;
}

- (BOOL)isDisplayingPageForIndex:(NSUInteger)index {
    BOOL foundPage = NO;
    for (ImageScrollView *page in visiblePages) {
        if (page.index == index) {
            foundPage = YES;
            break;
        }
    }
    return foundPage;
}

- (void)configurePage:(ImageScrollView *)page forIndex:(NSUInteger)index {
    page.index = index;
    page.frame = [self frameForPageAtIndex:index];

    NSLog(@"PhotoViewController - configurePage : bounds = %@", NSStringFromCGRect(pagingScrollView.bounds));

    [page displayImage:[dataSource imageForImageId:index]];

    NSLog(@"PhotoViewController - configurePage 2 : bounds = %@", NSStringFromCGRect(pagingScrollView.bounds));
}


#pragma mark -
#pragma mark ScrollView delegate methods

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    [self processPages];
}


#pragma mark -
#pragma mark  Frame calculations
#define PADDING  10

- (CGRect)frameForPagingScrollView {
    CGRect frame = [[UIScreen mainScreen] bounds];
    frame.origin.x -= PADDING;
    frame.size.width += (2*PADDING);
    return frame;
}

- (CGRect)frameForPageAtIndex:(NSUInteger)index {
    CGRect pagingScrollViewFrame = [self frameForPagingScrollView];

    CGRect pageFrame = pagingScrollViewFrame;
    pageFrame.size.width -= (2 * PADDING);
    pageFrame.origin.x = (pagingScrollViewFrame.size.width * index) + PADDING;
    //pageFrame.origin.x = (pagingScrollViewFrame.size.width * index) - (PADDING*index*2);
    return pageFrame;
}

ImageScrollView.h

@interface ImageScrollView : UIScrollView <UIScrollViewDelegate> {
    UIView        *imageView;
    NSUInteger     index;
}
@property (assign) NSUInteger index;

- (void)displayImage:(UIImage *)image;
//- (void)displayTiledImageNamed:(NSString *)imageName size:(CGSize)imageSize;
- (void)configureForImageSize:(CGSize)imageSize;

ImageScrollView.m

- (void)layoutSubviews 
{
    [super layoutSubviews];

    imageView.backgroundColor = [UIColor greenColor];
    self.backgroundColor = [UIColor blueColor];

    // center the image as it becomes smaller than the size of the screen

    CGSize boundsSize = self.bounds.size;
    CGRect frameToCenter = imageView.frame;

    // center horizontally
    if (frameToCenter.size.width < boundsSize.width)
        frameToCenter.origin.x = (boundsSize.width - frameToCenter.size.width) / 2;
    else
        frameToCenter.origin.x = 0;

    // center vertically
    if (frameToCenter.size.height < boundsSize.height)
        frameToCenter.origin.y = (boundsSize.height - frameToCenter.size.height) / 2;
    else
        frameToCenter.origin.y = 0;

    imageView.frame = frameToCenter;
    NSLog(@"imageView frame = %@", NSStringFromCGRect(frameToCenter));

    if ([imageView isKindOfClass:[TilingView class]]) {
        // to handle the interaction between CATiledLayer and high resolution screens, we need to manually set the
        // tiling view's contentScaleFactor to 1.0. (If we omitted this, it would be 2.0 on high resolution screens,
        // which would cause the CATiledLayer to ask us for tiles of the wrong scales.)
        imageView.contentScaleFactor = 1.0;
    }
}

#pragma mark -
#pragma mark UIScrollView delegate methods

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView
{
    return imageView;
}

#pragma mark -
#pragma mark Configure scrollView to display new image (tiled or not)

- (void)displayImage:(UIImage *)image
{
    // clear the previous imageView
    [imageView removeFromSuperview];
    [imageView release];
    imageView = nil;

    // reset our zoomScale to 1.0 before doing any further calculations
    self.zoomScale = 1.0;

    // make a new UIImageView for the new image
    imageView = [[UIImageView alloc] initWithImage:image];
    [self addSubview:imageView];

    [self configureForImageSize:[image size]];
}

- (void)configureForImageSize:(CGSize)imageSize 
{
    CGSize boundsSize = [self bounds].size;

    // set up our content size and min/max zoomscale
    CGFloat xScale = boundsSize.width / imageSize.width;    // the scale needed to perfectly fit the image width-wise
    CGFloat yScale = boundsSize.height / imageSize.height;  // the scale needed to perfectly fit the image height-wise
    CGFloat minScale = MIN(xScale, yScale);                 // use minimum of these to allow the image to become fully visible

    // on high resolution screens we have double the pixel density, so we will be seeing every pixel if we limit the
    // maximum zoom scale to 0.5.
    CGFloat maxScale = /*1.0 / */[[UIScreen mainScreen] scale];

    // don't let minScale exceed maxScale. (If the image is smaller than the screen, we don't want to force it to be zoomed.) 
    if (minScale > maxScale) {
        minScale = maxScale;
    }

    self.contentSize = imageSize;
    self.maximumZoomScale = maxScale;
    self.minimumZoomScale = minScale;
    self.zoomScale = minScale;  // start out with the content fully visible
}

我的问题是，当我第一次加载 PhotoViewController 实例时， pagingScrollView 偏移到 (0, -64) 像素的原点(我想是状态栏 + 导航栏的高度)。这会导致界面困惑，其中 ImageScrollView 出现在导航栏(原点 (0, 0))下方，即使其高度小于屏幕，也可以上下滚动。

通过一些日志和断点，我能够确定 pagingScrollView 边界在加载过程开始时没有问题。当我缩放 ImageScrollView 的图像以适合屏幕时，它们会发生变化。这会导致调用 viewForZoomingInScrollView 和scrollViewDidScroll 方法。 pagingScrollView 在这些调用期间发生偏移。

我尝试手动设置偏移量，但是当我在 processPages 中设置偏移量时，scrollView 无法再上下弹跳...

任何帮助将不胜感激!

干杯

PB

Answer 1

在您的特定情况下(即 PhotoViewController 被推送到 UINavigationController 堆栈上) - 导航栏将 contentInset 添加到 PhotoViewController 的 ScrollView 。这一切都得到了更好的解释here和 here 。

也就是说，PhotoViewController View 与窗口边界不紧密配合，因此有向各个方向滚动的空间。

我找到了解决您问题的 2 种可能的解决方案。

1 - 您需要手动调整 pagingScrollView 的 contentInset 以补偿导航栏和状态栏的高度。将其添加到PhotoViewController:

- (void)viewDidLoad {
    [super viewDidLoad];

    CGFloat topOffset = self.navigationController.navigationBar.frame.size.height + [[UIApplication sharedApplication] statusBarFrame].size.height;
    pagingScrollView.contentInset = UIEdgeInsetsMake(-topOffset, 0.0, 0.0, 0.0);
}

或

2 - 由于只有 ScrollView 才有 contentInset，因此将 pagingScrollView 包装在普通的 UIView 中:

- (void)loadView {    
    [self setWantsFullScreenLayout:YES];

    CGRect pagingScrollViewFrame = [self frameForPagingScrollView];
    photoView = [[UIView alloc] initWithFrame:pagingScrollViewFrame];
    pagingScrollView = [[UIScrollView alloc] initWithFrame:pagingScrollViewFrame];

    // ... configure the pagingScrollView

    [photoView addSubview:pagingScrollView];
    self.view = photoView;

    // ...
}

希望这有帮助!