如何使UICollectionViewFlowLayout itemSize动态适合屏幕大小 [英] How to make UICollectionViewFlowLayout itemSize dynamic for screen size

问题描述

我正在以编程方式工作(没有情节提要)，并且无法针对不同的屏幕尺寸动态设置layout.itemSize.我收到此错误消息:

I am working programmatically (no storyboard) and am having trouble making layout.itemSize dynamic for different screen sizes. I get this error message:

"UICollectionView必须使用非空布局参数初始化"

"UICollectionView must be initialised with a non-nil layout parameter"

在我的实现文件中包含以下代码:

with the following code in my implementation file:

- (instancetype)init 
{
    UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];

    CGSize size = self.collectionView.bounds.size;

    layout.itemSize = CGSizeMake(size.width, size.height);

    [layout setScrollDirection:UICollectionViewScrollDirectionVertical];

    layout.minimumLineSpacing = 100.0;

    layout.headerReferenceSize = CGSizeMake(0.0, 50.0);

    return (self = [super initWithCollectionViewLayout:layout]);
}

例如，对于 layout.itemSize 使用"100,100"，我不会收到错误消息.有办法使它动态吗?

I don't get the error message if I use "100,100" for example for layout.itemSize. Is there a way to make it dynamic though?

我是Objective-C的新手，所以很感谢我对我做错的事情的帮助.

I am new to Objective-C so would appreciate any help on what I am doing incorrectly.

推荐答案

需要使用流委托方法:

- (CGSize)collectionView:(UICollectionView *)collectionView
                  layout:(UICollectionViewLayout *)collectionViewLayout
  sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    CGSize cellSize = CGSizeMake(width, height);

    return cellSize;
}

您可以将宽度和高度浮点值指定为所需的任何值.

You specify the width and height float values to whatever you want.

例如，假设您的CollectionView是垂直的，并且您想要一个短的页眉视图，一个大的中间视图和一个小的页脚视图，那么您可以执行以下操作:

For example, lets say your CollectionView is vertical and you want a short header view, a big middle view and a small footer view, then you could do something like:

- (CGSize)collectionView:(UICollectionView *)collectionView
                  layout:(UICollectionViewLayout *)collectionViewLayout
  sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    CGSize cellSize;

    cellSize.width = self.view.bounds.size.width;

    if(indexPath.row == 0)
    {
        // header view height
        cellSize.height = 100;
    }
    else if(indexPath.row == 1)
    {
        // body view height
        cellSize.height = 500;
    }
    else
    {
        // assuming number of items is 3, then footer view is last view
        // footer view height
        cellSize.height = 100;
    }

    return cellSize;
}

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