NSCollectionView-拖动显示一个“空" -希望它看起来像Finder [英] NSCollectionView - dragging shows a "hole" - want it to look lke the Finder

问题描述

我有一个NSCollectionView.当我拖动项目时(在视图周围或视图外部)，我得到了正确的外观，但是在发生拖动时该单元格为空(请参见下面的动画GIF).所需的行为就像Finder一样-也就是说，图标应保留在原处，并且已拖动的图像也将显示在其中.

I have an NSCollectionView. When I drag items (around the view, or outside of the view), I get the right appearance, but the cell is empty while the dragging occurs (see animated GIF below). The desired behavior is to be like the Finder - that is, the icon should remain in place and the dragged image appears in addition to it.

我尝试了各种各样的事情都徒劳无功.例如，我尝试将拖动操作设置为sourceOperationMaskForDraggingContext中的Copy.不记得其他人了-他们失败了，所以我删除了实验.拖动完成后，所有内容都会正确更新，但是在拖动过程中，它看起来是错误的.

I have tried a variety of things to no avail. For example, I tried setting the drag operation to Copy in sourceOperationMaskForDraggingContext. Can't remember the other ones - they failed so I deleted the experiments. When the drag completes, everything updates properly, but during the drag it looks wrong.

是否有一种(希望很简单的方法)使NSCollectionView在拖动时更像Finder?谢谢.

Is there a (hopefully easy) way to get NSCollectionView to act more like the Finder when dragging? Thanks.

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推荐答案

这似乎与

我最初的解决方案是对集合视图项使用自定义视图.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在更改布局时也会隐藏项目视图.

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)在我的应用程序中运行良好.开始拖动时，我将取消隐藏项目视图.

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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