Question

我在尝试创建类似于Spotify的播放器中的UICollectionView时遇到了很多困难：

a busy cat

问题对我来说有两个问题。

1）如何使细胞居中，以便您可以看到中间细胞以及左侧和右侧细胞。

如果我创建方形的单元格并在每个单元格之间添加间距，则单元格会正确显示但不居中。

2）使用pagingEnabled = YES，collectionview正确地从一个页面滑动到另一个页面。但是，如果没有单元格居中，它只是将集合视图移动到页面上，该页面是屏幕的宽度。所以问题是如何让页面移动，以便你获得上述效果。

3）如何移动细胞的大小动画

我不想太担心这件事。如果我能做到这一点就会很好，但更难的问题是1和2。

我目前的代码是一个简单的UICollectionView，它具有正常的委托设置和自定义的UICollectionview单元格。也许我需要继承子类UICollectionViewFlowLayout？或者我可能需要将pagingEnabled变为NO，然后使用自定义滑动事件？会喜欢任何帮助！

Answer 1

为了创建水平轮播布局，您必须继承UICollectionViewFlowLayout，然后覆盖targetContentOffset(forProposedContentOffset:withScrollingVelocity:)，layoutAttributesForElements(in:)和shouldInvalidateLayout(forBoundsChange:)。

以下Swift 4.1 - iOS 11完整代码显示了如何实现它们。

CollectionViewController.swift

import UIKit

class CollectionViewController: UICollectionViewController {

    let collectionDataSource = CollectionDataSource()
    let flowLayout = ZoomAndSnapFlowLayout()

    override func viewDidLoad() {
        super.viewDidLoad()

        title = "Zoomed & snapped cells"

        guard let collectionView = collectionView else { fatalError() }
        //collectionView.decelerationRate = .fast // uncomment if necessary
        collectionView.dataSource = collectionDataSource
        collectionView.collectionViewLayout = flowLayout
        collectionView.register(CollectionViewCell.self, forCellWithReuseIdentifier: "Cell")
    }

}

ZoomAndSnapFlowLayout.swift

import UIKit

class ZoomAndSnapFlowLayout: UICollectionViewFlowLayout {

    let activeDistance: CGFloat = 200
    let zoomFactor: CGFloat = 0.3

    override init() {
        super.init()

        scrollDirection = .horizontal
        minimumLineSpacing = 40
        itemSize = CGSize(width: 150, height: 150)
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func prepare() {
        guard let collectionView = collectionView else { fatalError() }
        let verticalInsets = (collectionView.frame.height - collectionView.adjustedContentInset.top - collectionView.adjustedContentInset.bottom - itemSize.height) / 2
        let horizontalInsets = (collectionView.frame.width - collectionView.adjustedContentInset.right - collectionView.adjustedContentInset.left - itemSize.width) / 2
        sectionInset = UIEdgeInsets(top: verticalInsets, left: horizontalInsets, bottom: verticalInsets, right: horizontalInsets)

        super.prepare()
    }

    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        guard let collectionView = collectionView else { return nil }
        let rectAttributes = super.layoutAttributesForElements(in: rect)!.map { $0.copy() as! UICollectionViewLayoutAttributes }
        let visibleRect = CGRect(origin: collectionView.contentOffset, size: collectionView.frame.size)

        // Make the cells be zoomed when they reach the center of the screen
        for attributes in rectAttributes where attributes.frame.intersects(visibleRect) {
            let distance = visibleRect.midX - attributes.center.x
            let normalizedDistance = distance / activeDistance

            if distance.magnitude < activeDistance {
                let zoom = 1 + zoomFactor * (1 - normalizedDistance.magnitude)
                attributes.transform3D = CATransform3DMakeScale(zoom, zoom, 1)
                attributes.zIndex = Int(zoom.rounded())
            }
        }

        return rectAttributes
    }

    override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint {
        guard let collectionView = collectionView else { return .zero }

        // Add some snapping behaviour so that the zoomed cell is always centered
        let targetRect = CGRect(x: proposedContentOffset.x, y: 0, width: collectionView.frame.width, height: collectionView.frame.height)
        guard let rectAttributes = super.layoutAttributesForElements(in: targetRect) else { return .zero }

        var offsetAdjustment = CGFloat.greatestFiniteMagnitude
        let horizontalCenter = proposedContentOffset.x + collectionView.frame.width / 2

        for layoutAttributes in rectAttributes {
            let itemHorizontalCenter = layoutAttributes.center.x
            if (itemHorizontalCenter - horizontalCenter).magnitude < offsetAdjustment.magnitude {
                offsetAdjustment = itemHorizontalCenter - horizontalCenter
            }
        }

        return CGPoint(x: proposedContentOffset.x + offsetAdjustment, y: proposedContentOffset.y)
    }

    override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
        // Invalidate layout so that every cell get a chance to be zoomed when it reaches the center of the screen
        return true
    }

    override func invalidationContext(forBoundsChange newBounds: CGRect) -> UICollectionViewLayoutInvalidationContext {
        let context = super.invalidationContext(forBoundsChange: newBounds) as! UICollectionViewFlowLayoutInvalidationContext
        context.invalidateFlowLayoutDelegateMetrics = newBounds.size != collectionView?.bounds.size
        return context
    }

}

CollectionDataSource.swift

import UIKit

class CollectionDataSource: NSObject, UICollectionViewDataSource {

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 9
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! CollectionViewCell
        return cell
    }

}

CollectionViewCell.swift

import UIKit

class CollectionViewCell: UICollectionViewCell {

    override init(frame: CGRect) {
        super.init(frame: frame)

        contentView.backgroundColor = .green
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

}

预期结果：

来源：

WWDC 2012 session 219 - "Advanced Collection Views and Building Custom Layouts"

Answer 2

好吧，我昨天让UICollectionview像这样移动。

我可以与您分享我的代码：）

这是我的故事板

确保取消选中“已启用分页”

这是我的代码。

@interface FavoriteViewController () <UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout>
{
    NSMutableArray * mList;

    CGSize cellSize;
}

@property (weak, nonatomic) IBOutlet UICollectionView *cv;
@end

@implementation FavoriteViewController

- (void) viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];

    // to get a size.
    [self.view setNeedsLayout];
    [self.view layoutIfNeeded];

    CGRect screenFrame = [[UIScreen mainScreen] bounds];
    CGFloat width = screenFrame.size.width*self.cv.frame.size.height/screenFrame.size.height;
    cellSize = CGSizeMake(width, self.cv.frame.size.height);
    // if cell's height is exactly same with collection view's height, you get an warning message.
    cellSize.height -= 1;

    [self.cv reloadData];

    // setAlpha is for hiding looking-weird at first load
    [self.cv setAlpha:0];
}

- (void) viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];

    [self scrollViewDidScroll:self.cv];
    [self.cv setAlpha:1];
}

#pragma mark - scrollview delegate
- (void) scrollViewDidScroll:(UIScrollView *)scrollView
{
    if(mList.count > 0)
    {
        const CGFloat centerX = self.cv.center.x;
        for(UICollectionViewCell * cell in [self.cv visibleCells])
        {
            CGPoint pos = [cell convertPoint:CGPointZero toView:self.view];
            pos.x += cellSize.width/2.0f;
            CGFloat distance = fabs(centerX - pos.x);

// If you want to make side-cell's scale bigger or smaller,
// change the value of '0.1f'
            CGFloat scale = 1.0f - (distance/centerX)*0.1f;
            [cell setTransform:CGAffineTransformMakeScale(scale, scale)];
        }
    }
}

- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset
{ // for custom paging
    CGFloat movingX = velocity.x * scrollView.frame.size.width;
    CGFloat newOffsetX = scrollView.contentOffset.x + movingX;

    if(newOffsetX < 0)
    {
        newOffsetX = 0;
    }
    else if(newOffsetX > cellSize.width * (mList.count-1))
    {
        newOffsetX = cellSize.width * (mList.count-1);
    }
    else
    {
        NSUInteger newPage = newOffsetX/cellSize.width + ((int)newOffsetX%(int)cellSize.width > cellSize.width/2.0f ? 1 : 0);
        newOffsetX = newPage*cellSize.width;
    }

    targetContentOffset->x = newOffsetX;
}

#pragma mark - collectionview delegate
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    return mList.count;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewCell * cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"list" forIndexPath:indexPath];

    NSDictionary * dic = mList[indexPath.row];

    UIImageView * iv = (UIImageView *)[cell.contentView viewWithTag:1];
    UIImage * img = [UIImage imageWithData:[dic objectForKey:kKeyImg]];
    [iv setImage:img];

    return cell;
}

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    return cellSize;
}
- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section
{
    CGFloat gap = (self.cv.frame.size.width - cellSize.width)/2.0f;
    return UIEdgeInsetsMake(0, gap, 0, gap);
}
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section
{
    return 0;
}
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section
{
    return 0;
}

以make cell为中心的密钥代码是

scrollViewWillEndDragging
insetForSectionAtIndex

动画大小的关键代码是

scrollviewDidScroll

我希望这可以帮助你

P.S。如果您想像上传的图像一样更改alpha，请在scrollViewDidScroll中添加[cell setalpha]

Answer 3

正如您在Objective-c代码中所说的那样，有一个非常有名的库iCarousel可以帮助您完成您的需求。链接：https://github.com/nicklockwood/iCarousel

您可以使用＆＃39; Rotary＆＃39;或者＆＃39;线性＆＃39;或其他一些很少或没有修改的样式来实现自定义视图

要实现它，你只实现了它的一些委托方法，并且它为ex工作：

//specify the type you want to use in viewDidLoad
_carousel.type = iCarouselTypeRotary;

//Set the following delegate methods
- (NSInteger)numberOfItemsInCarousel:(iCarousel *)carousel
{
    //return the total number of items in the carousel
    return [_items count];
}

- (UIView *)carousel:(iCarousel *)carousel viewForItemAtIndex:(NSInteger)index reusingView:(UIView *)view
{
    UILabel *label = nil;

    //create new view if no view is available for recycling
    if (view == nil)
    {
        //don't do anything specific to the index within
        //this `if (view == nil) {...}` statement because the view will be
        //recycled and used with other index values later
        view = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 200.0f, 200.0f)];
        ((UIImageView *)view).image = [UIImage imageNamed:@"page.png"];
        view.contentMode = UIViewContentModeCenter;

        label = [[UILabel alloc] initWithFrame:view.bounds];
        label.backgroundColor = [UIColor clearColor];
        label.textAlignment = NSTextAlignmentCenter;
        label.font = [label.font fontWithSize:50];
        label.tag = 1;
        [view addSubview:label];
    }
    else
    {
        //get a reference to the label in the recycled view
        label = (UILabel *)[view viewWithTag:1];
    }

    //set item label
    label.text = [_items[index] stringValue];

    return view;
}

- (CGFloat)carousel:(iCarousel *)carousel valueForOption:(iCarouselOption)option withDefault:(CGFloat)value
{
    if (option == iCarouselOptionSpacing)
    {
        return value * 1.1;
    }
    return value;
}

您可以查看来自＆＃39; Examples/Basic iOS Example＆＃39;的完整工作演示。它包含在Github存储库链接

中

由于它很老而且很流行，你可以找到一些相关的教程，它也会比自定义代码实现更稳定

Answer 4

一段时间后我想要类似的行为，在@Mike_M的帮助下，我能够弄明白。虽然有很多很多方法可以做到这一点，但这个特殊的实现是创建一个自定义的UICollectionViewLayout。

以下代码（可在此处找到要点：https://gist.github.com/mmick66/9812223）

现在设置以下内容非常重要：*yourCollectionView*.decelerationRate = UIScrollViewDecelerationRateFast，这可以防止快速滑动跳过单元格。

这应该涵盖第1部分和第2部分。现在，对于第3部分，您可以通过不断地进行无效和更新将其合并到自定义collectionView中，但如果您问我，这有点麻烦。因此，另一种方法是在CGAffineTransformMakeScale( , )中设置UIScrollViewDidScroll，您可以根据距离屏幕中心的距离动态更新单元格的大小。

您可以使用[*youCollectionView indexPathsForVisibleItems]获取collectionView的可见单元格的indexPaths，然后获取这些indexPath的单元格。对于每个单元格，计算其中心到 yourCollectionView 的中心的距离

可以使用这个漂亮的方法找到collectionView的中心：CGPoint point = [self.view convertPoint:*yourCollectionView*.center toView:*yourCollectionView];

现在设置一条规则，即如果单元格的中心距离x不远，则单元格的大小例如是“正常大小”，称之为“1”。它到达中心，越接近正常尺寸2的两倍。

然后你可以使用以下if / else想法：

 if (distance > x) {
        cell.transform = CGAffineTransformMakeScale(1.0f, 1.0f);
 } else if (distance <= x) {

        float scale = MIN(distance/x) * 2.0f;
        cell.transform = CGAffineTransformMakeScale(scale, scale);
 }

细胞的大小将完全跟随您的触摸。如果您有任何其他问题，请告诉我，因为我将大部分内容写成了我的头脑。）

- (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)offset 
                             withScrollingVelocity:(CGPoint)velocity {

CGRect cvBounds = self.collectionView.bounds;
CGFloat halfWidth = cvBounds.size.width * 0.5f;
CGFloat proposedContentOffsetCenterX = offset.x + halfWidth;

NSArray* attributesArray = [self layoutAttributesForElementsInRect:cvBounds];

UICollectionViewLayoutAttributes* candidateAttributes;
for (UICollectionViewLayoutAttributes* attributes in attributesArray) {

    // == Skip comparison with non-cell items (headers and footers) == //
    if (attributes.representedElementCategory != 
        UICollectionElementCategoryCell) {
        continue;
    }

    // == First time in the loop == //
    if(!candidateAttributes) {
        candidateAttributes = attributes;
        continue;
    }

    if (fabsf(attributes.center.x - proposedContentOffsetCenterX) < 
        fabsf(candidateAttributes.center.x - proposedContentOffsetCenterX)) {
        candidateAttributes = attributes;
    }
}

return CGPointMake(candidateAttributes.center.x - halfWidth, offset.y);

}

Answer 5

不应启用

pagingEnabled，因为它需要每个单元格都是您查看的宽度，因为您需要查看其他单元格的边缘。对于你的第1点和第2点。我想你会从我最近的一个问题的答案中找到你需要的here。

单元格大小的动画可以通过继承UIcollectionviewFlowLayout并覆盖layoutAttributesForItemAtIndexPath:来实现，修改首先调用super提供的布局属性，然后根据与窗口相关的位置修改布局属性大小中央。

希望这会有所帮助。

Answer 6

如果您希望单元格之间的间距一致，您可以替换 Imanou Petit 解决方案中 ZoomAndSnapFlowLayout 中的以下方法：

override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
    guard let collectionView = collectionView else { return nil }
    let rectAttributes = super.layoutAttributesForElements(in: rect)!.map { $0.copy() as! UICollectionViewLayoutAttributes }
    let visibleRect = CGRect(origin: collectionView.contentOffset, size: collectionView.frame.size)
    let visibleAttributes = rectAttributes.filter { $0.frame.intersects(visibleRect) }

    // Keep the spacing between cells the same.
    // Each cell shifts the next cell by half of it's enlarged size.
    // Calculated separately for each direction.
    func adjustXPosition(_ toProcess: [UICollectionViewLayoutAttributes], direction: CGFloat, zoom: Bool = false) {
        var dx: CGFloat = 0

        for attributes in toProcess {
            let distance = visibleRect.midX - attributes.center.x
            attributes.frame.origin.x += dx

            if distance.magnitude < activeDistance {
                let normalizedDistance = distance / activeDistance
                let zoomAddition = zoomFactor * (1 - normalizedDistance.magnitude)
                let widthAddition = attributes.frame.width * zoomAddition / 2
                dx = dx + widthAddition * direction

                if zoom {
                    let scale = 1 + zoomAddition
                    attributes.transform3D = CATransform3DMakeScale(scale, scale, 1)
                }
            }
        }
    }

    // Adjust the x position first from left to right.
    // Then adjust the x position from right to left.
    // Lastly zoom the cells when they reach the center of the screen (zoom: true).
    adjustXPosition(visibleAttributes, direction: +1)
    adjustXPosition(visibleAttributes.reversed(), direction: -1, zoom: true)

    return rectAttributes
}

如何在Spotify的播放器中创建居中的UICollectionView

6 个答案: