设置节插入时，带有FlowLayout的UICollectionView不会滚动 [英] UICollectionView with FlowLayout not scrolling when setting section insets

问题描述

我正在以编程方式使用UICollectionView。

I am using a UICollectionView programmatically.

我将其框架设置如下：

UICollectionView *collectionView = [[UICollectionView alloc] initWithFrame:CGRectMake(0, 100, self.view.frame.size.width, 3000) collectionViewLayout:flowLayout];

我的 UICollectionViewFlowLayout 将部分插入设置为：

My UICollectionViewFlowLayout has a section inset set as:

flowLayout.sectionInset = UIEdgeInsetsMake(20.0, 20.0, 100.0, 20.0);

我也只有1个部分。

我已将高度设置为3,000，以查看集合视图是否会滚动但不会。我设置它，因为当我插入新项目时，集合视图似乎没有向上或向下滚动。

I've set the height to be 3,000 to see if the collection view would scroll but it doesn't. I am setting it to that since the collection view doesn't seem to scroll up or down when I insert new items.

UICollectionView 是 UIScrollView 的子类，这意味着我可以继续重置滚动视图的内容大小。这项工作是否正常？

UICollectionView is subclassed from a UIScrollView, which means I can keep resetting the scroll view content size. Would this work properly?

唯一的问题是，如果我知道所有项目的大小，包括每行有多少项，这将有效。

The only issue is that this would work if I know the sizes of all items including how many items are on each row.

如果每个项目的大小不同，我如何找出每行的大小？我需要添加所有行大小并增加 self.collectionView 的内容大小高度。

If each item had a different size, how would I find out the size of each row? I would need that to add all row sizes and increase the content size height of self.collectionView.

编辑

即使我上面的建议，重置内容大小，也无法正常工作！我在更新集合视图时尝试了以下操作：

Even my suggestion above, resetting the content size, does not work properly! I tried the following when updating my collection view:

 int numberOfRows = self.dataArray.count / 3;
self.collectionView.contentSize = CGSizeMake(self.view.frame.size.width, (numberOfRows * 200) + 300);

但这非常难看。这是因为它假设我的所有图像大小为200x200px，每行适合3个图像（因此除以3）。

This is very ugly though. This is because it assumes all my images are of size 200x200px, which fits 3 images per row (hence the division by 3).

此外，即使我拥有+300，最后一行我只能看到3/4而不是全部。我必须滚动更多，我将能够看到它，但它再次回到3/4。它有点像滚动刷新，如果你拖动它，视图只会移动，当你离开它时它会回到原来的位置。为什么会这样？只是Apple设计 UICollectionView 这么差吗？这有点荒谬...... UITableViews会根据自己的内容自动调整滚动。

Furthermore, even with the +300 that I have, the last row I can only see about 3/4 of it and not all of it. I have to scroll more and I will be able to see it but it goes back up again to 3/4. Its kind of like the scroll to refresh, where the view only moves if you drag it and when you leave it bumps back to where it was. Why is this happening? Is it just that Apple designed UICollectionView so poorly? This is a little ridiculous... UITableViews adjust their scroll according to their content automatically.

推荐答案

回答其他一些问题关于UICollectionView，我创建了这个演示项目，它滚动得很好，所以我不知道你有什么问题。我需要做的唯一事情是使最后一行完全可见是将底部插入的大小增加到90.我还为performBatchUpdates添加了一个完成方法：完成：自动滚动以便最后添加的项目可见（请注意，我使用performSelector; withObject：afterDelay :)添加了一些额外的项目。我的图像是48x48，我只是将我的集合视图设置为控制器视图的边界。下面是代码，您可以将它与您拥有的代码进行比较：

In answering some of your other questions about UICollectionView, I created this demo project, and it scrolls just fine, so I don't know what problem you're having. The only thing I needed to do to make the last row wholly visible was to increase the size of the bottom inset to 90. I also added a completion method to the performBatchUpdates:completion: to automatically scroll so that the last added item is visible (notice that I add some extra items by using performSelector;withObject:afterDelay:). My images are 48x48, and I just set my collection view to the bounds of my controller's view. Here is the code so you can compare it to what you have:

@interface ViewController () <UICollectionViewDataSource, UICollectionViewDelegateFlowLayout> {
NSMutableArray *newData;
}
 @property (nonatomic, retain) UICollectionView *collectionView;
 @property (nonatomic, retain) NSMutableArray *results;
 @end

@implementation ViewController

- (void)viewDidLoad {
    self.results = [NSMutableArray array];
    int i = 11;
    while (i<91) {
        UIImage *image = [UIImage imageNamed:[NSString stringWithFormat:@"New_PICT00%d.jpg",i]];
        [self.results addObject:image];
        i++;
    }

    UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init];
    //flowLayout.scrollDirection =  UICollectionViewScrollDirectionHorizontal;

    self.collectionView = [[UICollectionView alloc] initWithFrame:self.view.bounds collectionViewLayout:flowLayout];
    self.collectionView.dataSource = self;
    self.collectionView.delegate = self;
    self.view.backgroundColor = [UIColor blackColor];
    [self.view addSubview:self.collectionView];
    [self.collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"Cell"];
    //[self.collectionView registerClass:[RDCell class] forCellWithReuseIdentifier:@"myCell"];
    [self.collectionView reloadData];

    [self performSelector:@selector(addNewImages:) withObject:nil afterDelay:3];
}

-(void)addNewImages:(id)sender {
    newData = [NSMutableArray array];
    int i = 102;
    while (i<111) {
        UIImage *image = [UIImage imageNamed:[NSString stringWithFormat:@"New_PICT0%d.jpg",i]];
        [newData addObject:image];
        i++;
    }
    [self addNewCells];
}

-(void)addNewCells {
    NSMutableArray *arrayWithIndexPaths = [NSMutableArray array];
    [self.collectionView performBatchUpdates:^{
        int resultsSize = [self.results count];
        [self.results addObjectsFromArray:newData];
        for (int i = resultsSize; i < resultsSize + newData.count; i++)
            [arrayWithIndexPaths addObject:[NSIndexPath indexPathForRow:i inSection:0]];
        [self.collectionView insertItemsAtIndexPaths:arrayWithIndexPaths];
    }
    completion: ^(BOOL finished){
        [self.collectionView scrollToItemAtIndexPath:arrayWithIndexPaths.lastObject atScrollPosition:UICollectionViewScrollPositionCenteredVertically animated:YES];
    }];
}


- (NSInteger)collectionView:(UICollectionView *)view numberOfItemsInSection:(NSInteger)section {
    return [self.results count];
}

- (NSInteger)numberOfSectionsInCollectionView: (UICollectionView *)collectionView {
    return 1;
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"Cell" forIndexPath:indexPath];
    //cell.iv.image = [self.results objectAtIndex:indexPath.row];
    cell.backgroundColor = [UIColor colorWithPatternImage:[self.results objectAtIndex:indexPath.row]];
    return cell;
}


- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
    UIImage *image = [self.results objectAtIndex:indexPath.row];
    return CGSizeMake(image.size.width, image.size.height);
}

- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section {
    return UIEdgeInsetsMake(10, 10, 90, 10);
}

- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath {
    NSLog(@"Selected Image is Item %d",indexPath.row);
}

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