防止在拖动过程中NSCollectionView提起项目 [英] Prevent NSCollectionView 'lifting' an item during drag

问题描述

我知道如何在 NSCollectionView 中进行拖放，但是我似乎无法阻止它将项目从视图中移出。

I understand how to get drag and drop working for NSCollectionView but I can't seem to stop it 'lifting' the items off the view.

我当前的解决方案是不实施

My current solution is to not implement

func collectionView(_ collectionView: NSCollectionView, pasteboardWriterForItemAt indexPath: IndexPath) -> NSPasteboardWriting?

来自 NSCollectionViewDelegate ，以确保

func collectionView(_ collectionView: NSCollectionView, draggingImageForItemsAt indexPaths: Set<IndexPath>, with event: NSEvent, offset dragImageOffset: NSPointPointer) -> NSImage

IS ，我可以在其中提供自己的拖动图像。但是，这些不会聚集或提供显示正在拖动多少项目的图标。

IS called, where I can provide my own dragging images. However, these do not flock or provide the icon showing how many items are being dragged.

问题是，当我实现前一种方法时，我似乎无能为力（包括覆盖NSCollectionViewItem的 draggingImageComponents ）似乎可以防止将项目从集合视图中拖动出来，留下一个空白。

The problem is that when I implement the former method, nothing I seem to do (including overriding the NSCollectionViewItem's draggingImageComponents) seems to prevent the drag 'lifting' the item off the collection view, leaving behind an empty space.

拖动Photos.app中的图像和Finder.app中的文件（图标视图）不会抬起该项目，因此希望可以这样做。

Dragging images in Photos.app and files in Finder.app (icon view) do not lift the item so hopefully this is possible.

推荐答案

这似乎与 NSCollectionView-拖动显示一个洞-希望它看起来像Finder

我最初的解决方案是对集合视图使用自定义视图项目。在我的子类中，我重写了 setHidden：，以防止在拖动项目时集合视图隐藏我的项目视图。这有一些不良的副作用。看起来NSCollectionView在更改布局时也隐藏了项目视图。

My initial solution was to use a custom view for the collection view item. In my subclass I override setHidden: to prevent the collection view from hiding my item view while the item is being dragged. This had some undesirable side-effects. It appears that NSCollectionView also hides item views when changing the layout.

下一个想法（到目前为止）在我的应用程序中很好用。

The next idea (so far) works fine in my application. I un-hide the item views when dragging starts.

@interface HGImagesCollectionViewDelegate : NSObject <NSCollectionViewDelegate>

@end

@implementation HGImagesCollectionViewDelegate

- (void)collectionView:(NSCollectionView *)collectionView
       draggingSession:(NSDraggingSession *)session
      willBeginAtPoint:(NSPoint)screenPoint
  forItemsAtIndexPaths:(NSSet<NSIndexPath *> *)indexPaths
{
    //  Prevent item from being hidden (creating a hole in the grid) while being dragged
    for (NSIndexPath *indexPath in indexPaths) {
        [[[collectionView itemAtIndexPath:indexPath] view] setHidden:NO];
    }

    // …

}  

@end

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