如何在Spotify的Player中创建居中的UICollectionView

2020/12/08 00:21 · ios ·  · 0评论

我在尝试创建像这样的Spotify的Player中的UICollectionView时遇到很多困难:

忙碌的猫

我的问题有两个。

1)如何将单元格居中,以便您可以看到中间单元格以及左右单元格之一。

  • 如果创建正方形的单元格并在每个单元格之间添加间距,则这些单元格将正确显示,但不会居中。

2)使用pageingEnabled = YES,collectionview可以从一页正确滑动到另一页。但是,如果不将单元格居中放置,它只会将集合视图移动到整个页面(即屏幕的宽度)上。因此,问题是如何使页面移动,从而获得上述效果。

3)当细胞移动时,如何对它们的大小进行动画处理

  • 我不想为此担心太多。如果我可以解决这个问题,那将很棒,但更难的问题是1和2。

我当前拥有的代码是一个简单的UICollectionView,具有常规的委托设置和自定义的UICollectionview单元格(正方形)。也许我需要将UICollectionViewFlowLayout子类化吗?还是我需要将pageEnabled设置为NO,然后使用自定义滑动事件?希望有任何帮助!

正如您在评论中所说的那样,您希望在Objective-c代码中有一个非常著名的库,名为iCarousel,可以帮助您满足需求。链接:https//github.com/nicklockwood/iCarousel

您可以使用'Rotary'或'Linear'或其他样式,只需很少或不做任何修改即可实现自定义视图

要实现它,您仅实现了它的一些委托方法,并且它适用于ex:

//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;
}

您可以从Github存储库链接中随附的Examples / Basic iOS Example ”中查看完整的演示示例

由于它已经很老了并且很流行,所以您可以找到一些相关的教程,并且它比自定义代码实现要稳定得多。

为了创建一个旋转木马的水平布局,你得子类UICollectionViewFlowLayout,然后覆盖targetContentOffset(forProposedContentOffset:withScrollingVelocity:)layoutAttributesForElements(in:)shouldInvalidateLayout(forBoundsChange:)

以下Swift 5 / iOS 12.2完整代码展示了如何实现它们。


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.contentInsetAdjustmentBehavior = .always
        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:

在此处输入图片说明


资源:

好吧,昨天我使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“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;
}

使单元居中的关键代码是

  1. scrollViewWillEndDragging

  2. insetForSectionAtIndex

动画大小的关键码是

  1. scrollviewDidScroll

希望对您有帮助

PS:如果您想要像上载的图像一样更改Alpha,请在scrollViewDidScroll中添加[cell setalpha]

不久前,我想要类似的行为,在@Mike_M的帮助下,我得以弄清楚了。尽管有很多方法可以执行此操作,但是此特定实现是创建自定义UICollectionViewLayout。

下面的代码(可以在这里找到要点:https : //gist.github.com/mmick66/9812223

现在,重要的是设置以下各项:*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,但是如果您问我,这有点麻烦。因此,另一种方法是在中设置一个,您可以CGAffineTransformMakeScale( , )UIScrollViewDidScroll其中根据距屏幕中心的距离动态更新单元格的大小。

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

使用以下方法可以找到collectionView的中心: CGPoint point = [self.view convertPoint:*yourCollectionView*.center toView:*yourCollectionView];

现在设置一个规则,如果像元的中心距离x远,则像元的大小为“正常大小”,将其称为1。越靠近中心,则越接近两倍正常尺寸2。

那么您可以使用以下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);
 }

发生的情况是单元格的大小将完全按照您的触摸。让我知道您是否还有其他问题,因为我大部分都是在脑海中写的。

- (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);

}

pagingEnabled不应启用,因为它需要将每个单元格设置为视图的宽度,这对您不起作用,因为您需要查看其他单元格的边缘。为了您的点1和2,我想你会发现你所需要的在这里从我已故的回答另一个问题之一。

可以通过将UIcollectionviewFlowLayout子类化并覆盖layoutAttributesForItemAtIndexPath:其中,从而修改单元格大小的动画,该方法通过首先调用super来修改布局属性,然后根据与窗口中心相关的位置来修改布局属性的大小。

希望这会有所帮助。

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