Invoked periodically as the image is held within the destination area, allowing modification of the dragging operation or mouse-pointer position.
- macOS 10.0+
The object sending the message; use it to get details about the dragging operation.
For this to be invoked, the destination must have registered for the pasteboard data type involved in the drag operation. The messages continue until the image is either released or dragged out of the window or view.
This method provides the destination with an opportunity to modify the dragging operation depending on the position of the mouse pointer inside of the destination view or window object. For example, you may have several graphics or areas of text contained within the same view and wish to tailor the dragging operation, or to ignore the drag event completely, depending upon which object is underneath the mouse pointer at the time when the user releases the dragged image and the
perform method is invoked.
You typically examine the contents of the pasteboard in the
dragging method, where this examination is performed only once, rather than in the
dragging method, which is invoked multiple times.
Only one destination at a time receives a sequence of
dragging messages. If the mouse pointer is within the bounds of two overlapping views that are both valid destinations, the uppermost view receives these messages until the image is either released or dragged out.