iphone - 为什么 UIScrollView 会自动重置其 zoomScale 属性？

Question

我有一个扩展的 UIScrollView，它直接取自 Apple 文档示例项目“ZoomingPDFViewer”

如果你得到这个项目，你会注意到它的 UIScrollView 扩展类“PDFScrollView”在你运行它时有一个明显的错误(在 sim 和设备上)

如果您将缩放缩放得足够远，您最终会达到 StoryBoard 设置的缩放比例限制...但是随后，您可以重新缩放并继续超过限制。

我一直在尝试在自己的项目中实现这个类，而这个错误也随之而来。

出于某种原因，在缩放结束后，UIScrollView 的 zoomScale 属性被任意设置回 1.0，因此您可以有效地将缩放缩放到无限远...请记住，重置的 zoomScale 不会影响内容。 .. 所以您可以继续缩小，直到演示中的 PDF 只是屏幕上的一个像素。

我以前从未见过这个，我以前做过很多自定义 UIScrollView。

我已经尝试了几个步骤来解决它，但似乎没有任何效果。有谁知道什么会导致 UIScrollView 以这种方式重置其 zoomScale？

我认为这可能是因为在缩放期间删除和添加了 subview ，但我在 ScrollView 中放置了一个虚拟 View 作为 anchor ，但也没有用。

就像我说的.. ZoomingPDFViewer 是我正在使用的确切代码，使用 iOS 6.0

如有任何想法，我们将不胜感激。下面的示例代码

- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(float)scale
{
NSLog(@"Ending Zoom %0.2f %0.2f", [self zoomScale], scale);

// Set the new scale factor for the TiledPDFView.
_PDFScale *= scale;

// Calculate the new frame for the new TiledPDFView.
CGRect pageRect = CGPDFPageGetBoxRect(_PDFPage, kCGPDFMediaBox);
pageRect.size = CGSizeMake(pageRect.size.width*_PDFScale, pageRect.size.height*_PDFScale);


// Create a new TiledPDFView based on new frame and scaling.
TiledPDFView *tiledPDFView = [[TiledPDFView alloc] initWithFrame:pageRect scale:_PDFScale];
[tiledPDFView setPage:_PDFPage];

// Add the new TiledPDFView to the PDFScrollView.
[self addSubview:tiledPDFView];
self.tiledPDFView = tiledPDFView;

NSLog(@"End of end zoom %0.2f", [self zoomScale]);

}

这是结束滚动委托(delegate)...这两个日志都会产生一个 zoomScale，这正是您所期望的...所以...假设您实际缩放了 1.0 以外的任何数字。

然后调用 layoutSubviews..

// Use layoutSubviews to center the PDF page in the view.
- (void)layoutSubviews 
{
[super layoutSubviews];

// Center the image as it becomes smaller than the size of the screen.

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

// a bunch of code that sets frameToCenter

self.tiledPDFView.frame = frameToCenter;
self.backgroundImageView.frame = frameToCenter;

/*
 To handle the interaction between CATiledLayer and high resolution screens, set the tiling view's contentScaleFactor to 1.0.
 If this step were omitted, the content scale factor would be 2.0 on high resolution screens, which would cause the CATiledLayer to ask for tiles of the wrong scale.
 */
self.tiledPDFView.contentScaleFactor = 1.0;

NSLog(@"Subviews Layed Out %0.2f", [self zoomScale]);
}

此时，无论发生什么情况，zoomScale 都会报告回 1.0...这会在 End Zoom 委托(delegate)方法报告正确的缩放比例后跟踪 0.003 秒。

Answer 1

是的，这发生在 iOS 3 左右。zoomScale 始终相对于 ScrollView 的当前状态，而不是全局测量。每次缩放后，需要重新计算相对于当前整体缩放比例的最小和最大缩放比例。

这是我过去使用过的一些代码。它应该为您提供流程的要点:

尽早获取您需要的值:

- (void) viewDidLoad
{
    [super viewDidLoad];
    ...
    // Squirrel away min and max zoom values from nib
    sMinZoomScale = self.scrollView.minimumZoomScale; // the very minimum
    sMaxZoomScale = self.scrollView.maximumZoomScale; // the very maximum
    sGlobalZoomScale = 1.0f;  // we're currently at 100% size
    ...
}

然后是其余部分(self.navigationView 是 scrollView 的内容 View ):

- (void) scrollViewDidEndZooming:(UIScrollView *)scrollView
                        withView:(UIView *)view
                         atScale:(CGFloat)scale
{
    // after a zoom, change the resolution of our map
    sGlobalZoomScale *= scale;
    // Peg the scale to minZoom and maxZoom, in case of rounding errors
    sGlobalZoomScale = MIN(MAX(sMinZoomScale, sGlobalZoomScale), sMaxZoomScale);
    self.navigationView.globalZoomScale = sGlobalZoomScale;
    self.navigationView.globalScaleTransform = self.globalScaleTransform;
    [self updateResolution];

    // throw out all tiles so they'll reload at the new resolution
    [self.navigationView setNeedsDisplay];
}

// By the time we get here, the scrollview's applied a fake scale and translate transform, and
//   altered the scrollview's zoom scale. BUT, the navigationview is as it ever was.
- (void) updateResolution
{
    CGFloat zoomScale = [self.scrollView zoomScale];

    CGSize oldContentViewSize = self.navigationView.frame.size;    
    // zooming properly resets contentsize as it happens.
    CGSize newContentSize = self.scrollView.contentSize;

    CGPoint newContentOffset = self.scrollView.contentOffset;
    CGFloat xMult = newContentSize.width / oldContentViewSize.width;
    CGFloat yMult = newContentSize.height / oldContentViewSize.height;

    newContentOffset.x *= xMult;
    newContentOffset.y *= yMult;

    CGFloat currentMinZoom = self.scrollView.minimumZoomScale;
    CGFloat currentMaxZoom = self.scrollView.maximumZoomScale;

    CGFloat newMinZoom = currentMinZoom / zoomScale;
    CGFloat newMaxZoom = currentMaxZoom / zoomScale;

        // Reset zoom scales temporarily so we can patch up the revised content view
    // don't call our own set..zoomScale, 'cause they eventually call this method.  Infinite recursion is uncool.  
    [self.scrollView setMinimumZoomScale:1.0f];
    [self.scrollView setMaximumZoomScale:1.0f];
    [self.scrollView setZoomScale:1.0f animated:NO];

    [self.navigationView setFrame:CGRectMake(0.0f, 0.0f, newContentSize.width, newContentSize.height)];
    [self.scrollView setContentSize:newContentSize];
    [self.scrollView setContentOffset:newContentOffset animated:NO];

    [self.scrollView setMinimumZoomScale:newMinZoom];
    [self.scrollView setMaximumZoomScale:newMaxZoom];
}

希望这对您有所帮助。