Drag and Drop Caches the Background Bitmap
One of the Newton 2.x OS Q&As
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This document was exported on 7/23/97.
Drag and Drop Caches the Background Bitmap (7/15/96)
- Q: I am trying to implement drag scrolling. Although I can scroll the contents of the window, when I drag the item back into the window, it strips away the updated (scrolled) contents and leaves the original (unscrolled) contents behind. How can I get this to work?
A: Unfortunately, you have hit a design limitation of the Drag and Drop implementation. When you send the DragAndDrop message to a view, the bitmap for the pre-drag state is cached. Once the drag loop starts, you can not update that cached bitmap. When you "scroll" the view (probably using RefreshViews), you update the screen, but the cached bitmap is still there and is used by the DragAndDrop routine to update the screen as the dragged item is moved.