从 UICollectionView 获取单元格的屏幕位置 [英] Getting the screen location of a cell from a UICollectionView

问题描述

这与其说是一个问题，不如说是对如何解决这个问题的解释.

This isn't so much a question as an explanation of how to solve this problem.

首先要意识到 UICollectionView 确实继承自 UIScrollView - 因此使用滚动视图的内容进行标准查找是最好的解决方案.

The first thing to realize is that the UICollectionView does inherit from a UIScrollView - so doing a standard lookup with a scroll view's content is the best solution.

这是我要解决的问题:

我有一个 UICollectionView，每个单元格中都有不同的项目 - 以及不同类型的单元格.我需要选择一个单元格以使单元格中的图像看起来扩大并占据整个屏幕.我如何进行扩展是另一篇文章.

I had a UICollectionView that had differing items in each cell - along with differing types of cells. I need the selection of a cell to cause an effect of the image in the cell to appear to expand and take over the whole screen. How I did the expansion is for another post.

挑战在于获得单元格在屏幕上的位置，以便动画部分有一个从哪里开始的参考点.

The challenge was getting the cell's position on the screen so that the animating section would have a reference point from where to start.

因此，为了便于获取此信息 - 请考虑以下代码:

So, to facilitate getting this information - consider the following code:

第一注:

UICollectionView *picturesCollectionView;
DrawingCell cell; // -> instanceof UICollectionViewCell with custom items.

// first, get the list of cells that are visible on the screen - you must do this every time
// since the items can change...  This is a CRITICAL fact.  You do not go through the
// entire list of cells - only those the collectionView indicates are visible.  Note 
// there are some things to watch out for - the visibles array does not match the indexPath.item
// number - they are independent.  The latter is the item number overall the cells, while
// the visibles array may have only 2 entries - so there is NOT a 1-to-1 mapping - keep
// that in mind.

NSArray *visibles = [self.picturesCollectionView visibleCells];

// now, cycle through the times and find the one that matches some criteria.  In my
// case, check that the cell for the indexPath passed matches the cell's imageView...
// The indexPath was passed in for the method call - note that the indexPath will point
// to the number in your datasource for the particular item - this is crucial.

for (int i=0; i<visibles.count; i++) {
    DrawingCell *cell = (DrawingCell *)visibles[i];
    if (cell.imageView.image == (UIImage *)images[indexPath.item]) {

        // at this point, we've found the correct cell - now do the translation to determine
        // what is it's location on the current screen...  You do this by getting the contentOffset
        // from the collectionView subtracted from the cell's origin - and adding in (in my case)
        // the frame offset for the position of the item I wish to animate (in my case the
        // imageView contained within my custom collection cell...

        CGFloat relativeX = cell.frame.origin.x - self.picturesCollectionView.contentOffset.x + cell.imageView.frame.origin.x;
        CGFloat relativeY = cell.frame.origin.y - self.picturesCollectionView.contentOffset.y + cell.imageView.frame.origin.y;

        // I now have the exact screen coordinates of the imageView - so since I need this
        // to perform animations, I save it off in a CGRect - in my case, I set the size
        // exactly to the size of the imageView - so say you were doing a Flicker display
        // where you wanted to grow a selected image, you get the coordinates of the image
        // in the cell and the size from the displayed image...

        UIImageView *image = cell.imageView;

        // selectedCell is a CGRect that's global for the sake of this code...

        selectedCell = cell.frame;
        selectedCell.origin.x = relativeX;
        selectedCell.origin.y = relativeY;
        selectedCell.size.width = cell.imageView.frame.size.width;
        selectedCell.size.height = cell.imageView.frame.size.height;
    }
}

// done.  I have my coordinates and the size of the imageView I wish to animate and grow...

希望这可以帮助其他试图弄清楚如何在单元格上以确切位置覆盖某些内容的人等...

Hopefully, this helps other folks that are trying to figure out how to say overlay something on the cell in an exact position, etc...

推荐答案

-(void)collectionView:(UICollectionView *)cv didSelectItemAtIndexPath:(NSIndexPath *)indexPath;
{

UICollectionViewLayoutAttributes *attributes = [cv layoutAttributesForItemAtIndexPath:indexPath];

CGRect cellRect = attributes.frame;

CGRect cellFrameInSuperview = [cv convertRect:cellRect toView:[cv superview]];

NSLog(@"%f",cellFrameInSuperview.origin.x);
}

对我有用.你可以自己试试

It work for me.You can try yourself

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