我正在研究受UIPickerView启发的自定义值选择器.它看起来像这样:
正如您所看到的,此拾取器的主要特征之一是中央单元应该比其他单元更宽,以使其邻居在中央框架旁边可见.当您使用平移手势滚动选择器时,它应该动态更改中心值并根据上面的逻辑调整单元格.它的工作原理非常完美:
问题在于轻击手势.当用户通过点击它来选择选择器上的任何项目时,选择器试图滚动到该项目.但是,由于自定义布局UIScrollView滚动到错误的点,它的偏移被改变了.它看起来像这样:
当我尝试滚动到屏幕外单元格时,一切正常 – 该单元格不受布局的影响,并且它的坐标是正确的.这个问题仅针对可见细胞而上升.我完全没有任何关于如何解决这个问题的想法.你可以在这里找到整个项目:Carousel Collection View Test Project
请在下面找到一些重要的代码.
- // CarouselLayout.m
- - (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect {
- NSArray *array = [super layoutAttributesForElementsInRect:rect];
- CGRect visibleRect;
- visibleRect.origin = self.collectionView.contentOffset;
- visibleRect.size = self.collectionView.bounds.size;
- CGRect center = CGRectMake(CGRectGetMidX(visibleRect) - 1.0,0.0,2.0,CGRectGetHeight(visibleRect));
- CGFloat coreWidth = CGRectGetWidth(self.centralFrame) / 3.0;
- for (UICollectionViewLayoutAttributes *attributes in array) {
- if (CGRectIntersectsRect(attributes.frame,rect)){
- CGFloat distance = CGRectGetMidX(visibleRect) - attributes.center.x;
- CGFloat offset = 0.0;
- CGRect coreFrame = CGRectMake(attributes.center.x - (coreWidth / 2.0),coreWidth,CGRectGetHeight(self.centralFrame));
- if (CGRectIntersectsRect(center,coreFrame)) {
- if (attributes.indexPath.item % 2 == 0) {
- self.centralItemOffset = (CGRectGetWidth(self.centralFrame) - CGRectGetWidth(attributes.frame) - 4.0) / 2.0;
- if ([self.collectionView.delegate respondsToSelector:@selector(collectionView:layout:didChangeCentralItem:)]) {
- [(id <CarouselLayoutDelegate>)self.collectionView.delegate collectionView:self.collectionView layout:self didChangeCentralItem:attributes.indexPath];
- }
- }
- }
- offset = (distance > 0) ? -self.centralItemOffset : self.centralItemOffset;
- attributes.center = CGPointMake(attributes.center.x + offset,attributes.center.y);
- }
- }
- return array;
- }
- - (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset withScrollingVelocity:(CGPoint)velocity {
- CGFloat offsetAdjustment = MAXFLOAT;
- CGFloat horizontalCenter = proposedContentOffset.x + (CGRectGetWidth(self.collectionView.bounds) / 2.0);
- CGRect targetRectHorizontal = CGRectMake(proposedContentOffset.x,self.collectionView.bounds.size.width,self.collectionView.bounds.size.height);
- NSArray *array = [super layoutAttributesForElementsInRect:targetRectHorizontal];
- for (UICollectionViewLayoutAttributes *attributes in array) {
- if (attributes.indexPath.item % 2 == 1) {
- continue;
- }
- CGFloat itemHorizontalCenter = attributes.center.x;
- if (ABS(itemHorizontalCenter - horizontalCenter) < ABS(offsetAdjustment)) {
- offsetAdjustment = itemHorizontalCenter - horizontalCenter;
- }
- }
- return CGPointMake(proposedContentOffset.x + offsetAdjustment,proposedContentOffset.y);
- }
- // ViewController.m
- - (void)collectionView:(UICollectionView *)collectionView didHighlightItemAtIndexPath:(NSIndexPath *)indexPath {
- if (indexPath.item % 2 == 1) {
- return;
- }
- NSString *nextValue = [self valueAtIndexPath:indexPath];
- [self scrollToValue:nextValue animated:YES];
- self.currentValue = nextValue;
- }
- - (void)scrollToValue:(NSString *)value animated:(BOOL)animated {
- NSIndexPath *targetPath = nil;
- NSIndexPath *currentPath = nil;
- for (NSString *item in self.itemsArray) {
- if (!targetPath && [value isEqualToString:item]) {
- targetPath = [NSIndexPath indexPathForItem:([self.itemsArray indexOfObject:item] * 2) inSection:0];
- }
- if (!currentPath && [self.currentValue isEqualToString:item]) {
- currentPath = [NSIndexPath indexPathForItem:([self.itemsArray indexOfObject:item] * 2) inSection:0];
- }
- if (targetPath && currentPath) {
- break;
- }
- }
- if (targetPath && currentPath) {
- [self.itemsCollectionView scrollToItemAtIndexPath:targetPath atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:animated];
- }
- }
解决方法
在scrollToValue方法中更改:
- if (targetPath && currentPath) {
- [self.itemsCollectionView scrollToItemAtIndexPath:targetPath atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:animated];
- }
成:
- if (targetPath && currentPath) {
- if (targetPath.row < currentPath.row) {
- [self.itemsCollectionView scrollToItemAtIndexPath:[NSIndexPath indexPathForRow:self.itemsArray.count inSection:0] atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:animated];
- [self.itemsCollectionView scrollToItemAtIndexPath:targetPath atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:animated];
- } else {
- [self.itemsCollectionView scrollToItemAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:0] atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:animated];
- [self.itemsCollectionView scrollToItemAtIndexPath:targetPath atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:animated];
- }
- }
它会起作用.