无限UIScrollView在iOS4.3而不是iOS5中获得奇怪的行为 [英] Infinite UIScrollView gets strange behavior in iOS4.3 not iOS5

问题描述

我实现了一个包含UIViews的无限UIScrollView。在iOS5（模拟器和iphone）中滚动时，它可以很好地工作。但是在iOS 4.3（SIM和手机）中它有点疯狂，滚动传递的视图比它应该多（比iOS5大10-15倍的视图）。并且为了让它更奇怪，如果我慢慢拖动它会按预期工作，所以它在我释放后不会继续滚动。

I've implemented an infinite UIScrollView that contains UIViews. When scrolling in iOS5 (simulator and iphone) it works beautifully. But in iOS 4.3 (sim and phone) it kinda goes a bit crazy and scrolls passed more views than it should (about 10-15x more views than in iOS5). And to make it more strange it works as expected if I drag slowly so it doesn't continue scroll after I release.

设置有点简单，我扩展了UIScrollView类。并添加宽度约为1500pt的UIView，在此添加我想要滚动的UIViews。滚动时，如果视图不在屏幕上，则会添加和删除视图。

The setup is kinda simple, I extend the UIScrollView class. And add UIView with a width of about 1500pt, in this I add my UIViews I want to scroll over. When scrolling the views are added and removed if they are off screen.

我认为我的问题在于此代码：

I think my problem lies with in this code:

 - (void)recenterIfNecessary {
    CGPoint currentOffset = [self contentOffset];
    CGFloat contentWidth = [self contentSize].width;
    CGFloat centerOffsetX = (contentWidth - [self bounds].size.width) / 2.0;
    CGFloat distanceFromCenter = fabs(currentOffset.x - centerOffsetX);
    UIView *image;

    if (distanceFromCenter > (contentWidth / 4.0)) {
        // Recenter the ScrollView so we never reach the edge
        self.contentOffset = CGPointMake(centerOffsetX, currentOffset.y);
        // Move visiblePhotos to new position to adjust to new contentOffset
        for (image in visiblePhotos) {
            CGPoint center = image.center;
            center.x += (centerOffsetX - currentOffset.x);
            image.center = center;
        }
    }
}

在这里调用recenterIfNecessary ：

- (void)layoutSubviews {
    [super layoutSubviews];    
    [self recenterIfNecessary];
    [self tileImagesFromMinX:minVisibleX toMaxX:maxVisibleX];
    //....
}

我试过记录位置和偏移尝试找到iOS4和iOS之间差异的模式祝你好运。

I've tried logging positions and offsets to try find a pattern with the difference between iOS4 & 5 with luck.

我从 http://developer.apple.com/videos/wwdc/2011/#advanced-scrollview-techniques （他们使用的是iOS5）。

I got the concept and some code from http://developer.apple.com/videos/wwdc/2011/#advanced-scrollview-techniques (they use iOS5).

编辑

照片（放在visiblePhotos数组中）是使用以下方法创建的：

Photos (that are put in the visiblePhotos array) are created with this methods:

 - (CGFloat)placeNewImageOnRight:(CGFloat)rightEdge {
    imageIndex = imageIndex < 0 ? ([reportItems count] - 1) : (imageIndex >= [reportItems count]  ? 0 : imageIndex);

    UIView *image = [self createItemContainer:[reportItems objectAtIndex:imageIndex]];
    [visiblePhotos addObject:image];

    CGRect frame = [image frame];
    frame.origin.x = rightEdge;
    frame.origin.y = [imageContainerView bounds].size.height - frame.size.height;

    [image setFrame:frame];

    imageIndex += 1;

    return CGRectGetMaxX(frame);
}

- (CGFloat)placeNewImageOnLeft:(CGFloat)leftEdge {
    imageIndex = imageIndex < 0 ? ([reportItems count] - 1) : (imageIndex >= [reportItems count] ? 0 : imageIndex);

    UIView *image = [self createItemContainer:[reportItems objectAtIndex:imageIndex]];
    [visiblePhotos insertObject:image atIndex:0];

    CGRect frame = [image frame];
    frame.origin.x = leftEdge - frame.size.width;
    frame.origin.y = [imageContainerView bounds].size.height - frame.size.height;
    [image setFrame:frame];

    imageIndex -= 1;

    return CGRectGetMinX(frame);
}

[self createItemContainer：[reportItems objectAtIndex：imageIndex] ] 创建一个包含照片`的UIVeiw。

[self createItemContainer:[reportItems objectAtIndex:imageIndex]] creates a UIVeiw that contains a photo`.

左右方法基本相同，并由下面的方法调用。 在每个帧上调用 tileImagesFromMinX - （void）layoutSubviews 。

The left and right methods are basically the same and are invoked by the method below. And tileImagesFromMinX is invoked on every frame by - (void)layoutSubviews.

- (void)tileImagesFromMinX:(CGFloat)minVisibleX toMaxX:(CGFloat)maxVisibleX {
    if ([visiblePhotos count] == 0) {
        [self placeNewImageOnRight:minVisibleX];
    }

    UIView *lastImage = [visiblePhotos lastObject];
    CGFloat rightEdge = CGRectGetMaxX([lastImage frame]);
    while (rightEdge < maxVisibleX) {
        rightEdge = [self placeNewImageOnRight:rightEdge];
    }

    UIView *firstImage = [visiblePhotos objectAtIndex:0];
    CGFloat leftEdge = CGRectGetMinX([firstImage frame]);
    while (leftEdge > minVisibleX) {
        leftEdge = [self placeNewImageOnLeft:leftEdge];
    } 

    lastImage = [visiblePhotos lastObject];
    while ([lastImage frame].origin.x > maxVisibleX) {
        [lastImage removeFromSuperview];
        [visiblePhotos removeLastObject];
        lastImage = [visiblePhotos lastObject];
    }    

    firstImage = [visiblePhotos objectAtIndex:0];
    while (CGRectGetMaxX([firstImage frame]) < minVisibleX) {
        [firstImage removeFromSuperview];
        [visiblePhotos removeObjectAtIndex:0];
        firstImage = [visiblePhotos objectAtIndex:0];
    }
}

推荐答案

我已经完成了一堆调查，并确定你不能只设置 self.contentOffset = ...; 并期望滚动视图在iOS 4.3中正确滚动/减速。因此，即使没有图像平铺（事实上，如果删除图像并在图像容器视图中放置背景，您会更清楚地注意到这一点），您实现的 recenterIfNecessary 不会在4.3下工作（这也会影响开发者网站上的示例代码！）。

I've done a bunch of investigating and determined that you can't just set self.contentOffset = ...; and expect the scroll view to scroll/decelerate properly in iOS 4.3. So, even without the image tiling (and in fact you will notice this more clearly if you remove your images and just put a background on your image container view), your implementation of recenterIfNecessary will not work under 4.3 (this also affects the sample code on the developer site!).

不幸的是，似乎解决这个问题的唯一方法是覆盖 -setContentOffset：并在调用 super 之前修改那里的偏移量。请查看此问题，获取有关如何正常工作的一些指导。我希望你能用这个方法在iOS 5中运行...

Unfortunately, it seems the only way to work around this is to override -setContentOffset: and modify the offset there before calling super. Have a look at this question for some guidance on how to get that working correctly. I hope for your sake that this method will also work in iOS 5...

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