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因此，我正在修改 Apple 的 PhotoScroller 示例，并尝试添加无限循环功能，即：当用户滚动到最后一张图片时，接下来会显示第一张。

为此，我将 contentSize 宽度乘以 100（假死循环），将最后需要的页面索引也乘以 100，并使用假索引（索引模 self.imageCount）来显示正确的图像，如下：

- (CGSize)contentSizeForPagingScrollView {
    // We have to use the paging scroll view's bounds to calculate the contentSize, for the same reason outlined above.
    CGRect bounds = pagingScrollView.bounds;
    double rightBounds = bounds.size.height;
    // return CGSizeMake(bounds.size.width * [self imageCount], rightBounds); // no infinite loop
    return CGSizeMake(bounds.size.width * [self imageCount] * 100, rightBounds); // with infinite loop
}

- (void)tilePages 
{
    // Calculate which pages are visible
    CGRect visibleBounds = pagingScrollView.bounds;
    int firstNeededPageIndex = floorf(CGRectGetMinX(visibleBounds) / CGRectGetWidth(visibleBounds));
    int lastNeededPageIndex  = floorf((CGRectGetMaxX(visibleBounds)-1) / CGRectGetWidth(visibleBounds));
    firstNeededPageIndex = MAX(firstNeededPageIndex, 0);
    // lastNeededPageIndex  = MIN(lastNeededPageIndex, [self imageCount] - 1); // no infinite loop
    lastNeededPageIndex  = MIN(lastNeededPageIndex, [self imageCount] * 100 - 1); // with infinite loop

    // 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];

    int fakeIndex = firstNeededPageIndex;
    // add missing pages
    for (int index = firstNeededPageIndex; index <= lastNeededPageIndex; index++) {
        fakeIndex = index % self.imageCount;
        if (![self isDisplayingPageForIndex:fakeIndex]) {
            ImageScrollView *page = [self dequeueRecycledPage];
            if (page == nil) {
                page = [[ImageScrollView alloc] init];
            }
            [self configurePage:page forIndex:fakeIndex];
            [pagingScrollView addSubview:page];
            [visiblePages addObject:page];
        }
    }
}

因此，只要 index == fakeIndex，图片就可以正常显示，但是一旦循环超过该点，例如：index = 5，fakeIndex =1，页面将保持黑色并且不再显示图像。

但是，我可以使用控制台看到，当调用 [self configurePage:page forIndex:fakeIndex] 时，会获取正确的图像名称。

如果有人可以花一点时间调查原始示例代码（http://developer.apple.com/library/ios/#samplecode/PhotoScroller/Introduction/Intro.html），并找出问题所在，那就太好了.

谢谢你。

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1 回答 1

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问题在于：

- (CGRect)frameForPageAtIndex:(NSUInteger)index {
    // We have to use our paging scroll view's bounds, not frame, to calculate the page placement. When the device is in
    // landscape orientation, the frame will still be in portrait because the pagingScrollView is the root view controller's
    // view, so its frame is in window coordinate space, which is never rotated. Its bounds, however, will be in landscape
    // because it has a rotation transform applied.
    CGRect bounds = pagingScrollView.bounds;
    CGRect pageFrame = bounds;
    pageFrame.size.width -= (2 * PADDING);
    pageFrame.origin.x = (bounds.size.width * index) + PADDING;
    // pageFrame.origin.y -= 44;
    return pageFrame;
}

该框架将 fakeIndex 作为水平原点的乘数，因此新的页面框架被放置在第一个页面框架的顶部。通过将 fakeIndex 和 index 都传递给 [self configurePage:page forIndex:fakeIndex]，我可以将索引作为水平原点的乘数传递，这样新的页面框架就会是正确的。

于 2012-08-16T19:41:27.043 回答