在UIScrollView上以不同的速度滚动背景 [英] Scroll a background in a different speed on a UIScrollView

问题描述

当有人做一个擦除手势从左到右滚动内容时，我想让背景图像滚动到同一方向，但速度不同。就像20年前这些经典游戏所做的那样（记住，任何人????）

When somebody does a wipe gesture to scroll the content from left to right, I would like to have a background image scrolling into the same direction, but at a different speed. Much like what these classic games did do 20 years ago (remember that, anybody????)

推荐答案

我完成了这个使用两个 UIScrollView 实例。第一个是显示实际内容的位置，第二个（在z顺序中位于第一个后面）是我的移动速度较慢的背景。从那里顶部的 UIScrollView 附加了一个委托，当 contentOffset 发生变化时会收到通知。反过来，该委托以编程方式设置背景滚动条的 contentOffset ，与常量相乘以减慢相对于前景的向下滚动。因此，例如，您可能会有以下内容：

I accomplished this by using two UIScrollView instances. The first is where the actual content is displayed, and the second (which is behind the first in z-order) is where I have my slower-moving background. From there the top UIScrollView has a delegate attached to it that gets notified when the contentOffset changes. That delegate, in turn, programatically sets the contentOffset of the background scroller, multiplied against a constant to slow the scroll down relative to the foreground. So, for instance, you might have something like:

// Defined as part of the delegate for the foreground UIScrollView
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    UIScrollView* scroll_view(static_cast<UIScrollView*>(bkg_scroller_m.view));
    CGPoint       offset(scrollView.contentOffset);

    offset.x = offset.x / 3;
    offset.y = offset.y / 3;

    // Scroll the background scroll view by some smaller offset
    scroll_view.contentOffset = offset;
}

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