没有调用scrollViewDidEndDecelerating

发布于 2024-10-23 13:25:52 字数 217 浏览 5 评论 0原文

我有一个包含大图像的 UIScrollView，并使用分页在图像之间滚动。为了节省内存，我只加载当前可见图像之前和之后的一张图像，并在滚动完成后加载/释放新图像。当快速滚动并且未调用scrollViewDidEndDecelerating 时，就会出现此问题。当调用scrollViewDidEndDecelerating时，我想在活动页面中显示图像名称。

我该如何解决这个问题？为什么会出现这种情况？

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锦爱 2024-10-30 13:25:52

scrollViewDidEndDragging 将在每次滚动完成后调用

-(void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate{}

scrollViewDidEndDecelerating 不要在每次拖动时调用（如果拖动停止后不以加速速度拖动，则永远不会调用此函数） strong>

-(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView{}

scrollViewDidEndScrollingAnimation 如果您想使用 api 移动滚动视图而不是拖动，则会调用此 api。

-(void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView{}

scrollViewDidEndDragging will call after each scroll complete

-(void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate{}

scrollViewDidEndDecelerating don't call in each drag (if you don't drag with acce speed after draged stop it will don't never call this func)

-(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView{}

scrollViewDidEndScrollingAnimation if you want move the scroll view use api not with drag, this api will called.

-(void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView{}

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对不⑦ 2024-10-30 13:25:52

我用滚动视图做同样的事情——延迟加载图像。实际上，我们必须加载一个拉伸的缩略图（制作图像的模糊低分辨率版本），然后在页面实际 100% 显示在视图中时加载真实图像。

我要做的就是在scrollViewDidScroll:scrollView 中使用以下代码。

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{    
    if (!_isCurrentlyRotating) {
        CGFloat pageWidth = _scrollView.frame.size.width;
        int page = floor((_scrollView.contentOffset.x - pageWidth / 2) / pageWidth)+1;

        if (_currentPage != page)
            [self setCurrentPage:page];
    }
}

上面计算了将要显示的页面（当您滚动时）。当页面浏览量显示到 50% 时，它实际上会更改当前页码。这可以与页面控件结合使用以突出显示当前页面点。

使用上面的内容，（在滚动视图上启用分页）当用户使用手指更改页面（正常行为）时，当页面 100% 显示时，将调用scrollViewDidEndDecelerating:scrollView。我所说的 100% 是指您只能看到一页，而不能看到另一页的一部分。

但是我们在滚动视图的末尾有一个“重新开始”按钮，它调用我的scrollToPage：函数。

- (void) scrollToPage:(int)page {
    CGRect frame;
    frame.origin.x = self.scrollView.frame.size.width * page;
    frame.origin.y = 0;
    frame.size = self.scrollView.frame.size;
    [self.scrollView scrollRectToVisible:frame animated:YES];
}

使用scrollRectToVisible:animated:方法不会触发scrollViewDidEndDecelerating:方法，所以我只是添加了对这两个方法的sharpen方法（它只是在图像视图中加载高分辨率图像）调用，这样如果用户滚动或者如果按下重新开始按钮。

- (void) scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView {
    [self sharpenImageView];
}

- (void) scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
    [self sharpenImageView];
}

我希望这有帮助！

Im doing the same thing with a scroll view - lazy loading of images. We actually had to load a thumbnail that is stretched (making a blurry low res version of the image) and then load the real image when the page is actually being displayed 100% in view.

What I had to do was use the following code in the scrollViewDidScroll:scrollView.

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{    
    if (!_isCurrentlyRotating) {
        CGFloat pageWidth = _scrollView.frame.size.width;
        int page = floor((_scrollView.contentOffset.x - pageWidth / 2) / pageWidth)+1;

        if (_currentPage != page)
            [self setCurrentPage:page];
    }
}

The above calculates the page that is going to be displayed (as your scrolling). It will actually change the current page number when the page view is 50% displayed. This can be used in conjunction with the page control to highlight the current page dot.

Using the above, (with paging enabled on the scroll view) when the user uses their finger to change the page (the normal behavior) scrollViewDidEndDecelerating:scrollView is called when the page is 100% displayed. By 100% I mean you can only see one page not part of one part of another.

But we have a 'Start Over' button at the end of the scroll view that calls my scrollToPage: function.

- (void) scrollToPage:(int)page {
    CGRect frame;
    frame.origin.x = self.scrollView.frame.size.width * page;
    frame.origin.y = 0;
    frame.size = self.scrollView.frame.size;
    [self.scrollView scrollRectToVisible:frame animated:YES];
}

Using scrollRectToVisible:animated: method does not trigger the scrollViewDidEndDecelerating: method so I simply added the sharpen method (which simply loads te high res image in the image view) call to both methods so that it will be called if the user scrolls or if the start over button is pressed.

- (void) scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView {
    [self sharpenImageView];
}

- (void) scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
    [self sharpenImageView];
}

I hope this helps!

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