我需要以下要求的uiscrollview实现方面的帮助:分页带有延迟加载的UIScrollview
1)pagingEnabled = true。
2)懒惰页面加载。
3)页面在后台加载。所以我需要在第一次运行加载页面X,然后得到通知,该页面已完全加载,然后才允许用户滚动到它。
4)改变当前页面的能力。
我的第一次尝试是重写scrollViewDidEndDeacelerating和scrollViewDidScroll,但是我有一半的页面出现问题(当你停止滚动一半的页面,然后等待新页面添加到滚动)和空白页面(当用户滚动得太快时)。
我的第二次尝试是重写UIScrollView的layoutSubviews方法,并在那里做所有的计算。但它似乎非常复杂。
所以,我很想找到任何类似实现的例子。
现在我有这样的代码:
我实现scrollViewWillBeginDragging和scrollViewDidEndDecelerating:
- (void)scrollViewWillBeginDragging:(UIScrollView *)aScrollView
{
isScrolling = YES;
}
- (void)scrollViewDidEndDecelerating:(UIScrollView *)aScrollView
{
isScrolling = NO;
// Here we load the page that was prepared when the user was scrolling
if (needDisplay > -1) {
//NSLog(@"Loading queued page %d", needDisplay);
[self loadScrollViewWithPage:needDisplay forceAddToSuperview:NO animated:YES];
needDisplay = -1;
}
// minLoadedPageIndex - index of the first loaded page.
int selectedIndex = MIN(floor((aScrollView.contentOffset.x - pageWidth/2)/pageWidth) + 1 + minLoadedPageIndex, [photoItems count] - 1);
[self loadScrollViewWithPage:selectedIndex - 1 forceAddToSuperview:NO animated:YES];
[self loadScrollViewWithPage:selectedIndex forceAddToSuperview:NO animated:YES];
[self loadScrollViewWithPage:selectedIndex + 1 forceAddToSuperview:NO animated:YES];
}
在loadScrollViewWithPage我创造它加载的页面视图控制器来自服务器的数据在后台。直到它从服务器加载数据之前,我不会将视图添加到滚动视图。
- (void)loadScrollViewWithPage:(int)page forceAddToSuperview:(BOOL)value animated:(BOOL)animated
{
DetailController *controller = page >= viewControllers.count ? [NSNull null] :[viewControllers objectAtIndex:page];
if ((NSNull *)controller == [NSNull null])
{
controller = [[DetailController alloc] initWithNibName:@"DetailController" bundle:nil];
controller.delegate = self;
controller.view.hidden = NO; //this will call viewDidLoad.
if (page >= viewControllers.count) {
[viewControllers addObject:controller];
}
else {
[viewControllers replaceObjectAtIndex:page withObject:controller];
}
[controller release];
}
// add the controller's view to the scroll view
if (controller.view && controller.view.superview == nil && (controller.isLoadedOrFailed || value)) {
[self setNumberOfVisiblePages:visiblePagesCount+1];
if (page < selectedIndex) {
// We are adding the page to the left of the current page,
// so we need to adjust the content offset.
CGFloat offset = (int)scrollView.contentOffset.x % (int)scrollView.frame.size.width;
offset = scrollView.frame.size.width * (selectedIndex - minLoadedPageIndex) + offset;
[scrollView setContentOffset:CGPointMake(offset, 0.0) animated:animated];
}
CGRect frame = scrollView.frame;
frame.origin.x = frame.size.width * (page - minLoadedPageIndex);
frame.origin.y = 0;
controller.view.frame = frame;
[scrollView addSubview:controller.view];
[controller viewWillAppear:NO];
}
}
另外我有一个detailControllerDidFinishDownload方法当用于页面视图控制器数据已经加载被调用。
- (void)detailControllerDidFinishDownload:(DetailController *)controller
{
... //here I calculate new minLoadedPageIndex value
// reset pages frames
if (minLoadedPageIndex < oldMinPage) {
for(int i=oldMinPage;i < [viewControllers count]; i++) {
DetailController *detailsController = [viewControllers objectAtIndex:i];
if ((NSNull *)detailsController != [NSNull null]) {
CGRect frame = scrollView.frame;
frame.origin.x = frame.size.width * (i - minLoadedPageIndex);
frame.origin.y = 0;
[detailsController.view setFrame:frame];
}
}
}
// load the page now or delay load until the scrolling will be finished
if (!isScrolling) {
[self loadScrollViewWithPage:[photoItems indexOfObject:controller.photoItem] forceAddToSuperview:NO animated:NO];
}
else {
needDisplay = [photoItems indexOfObject:controller.photoItem];
//NSLog(@"pageControlUsed is used!!! %d", [photoItems indexOfObject:controller.photoItem]);
}
}
我现在的问题是,有时在页面的中间(或接近中间的某个位置)滚动stucks,它不会去最近的页面反弹,直到我稍微它。我的测试表明,如果我滚动出内容视图框架(滚动视图已弹起)并等待加载新页面,则会发生这种情况。在10次滚动时间中的1次。
谢谢米哈伊尔!
我不再需要在加载页面时停止滚动用户;显示进度指示器似乎更加用户友好,并且不需要中断UIScrollView的行为。 –
我的客户想要它,我无法劝他放弃它:( – MrZoidberg