API proposal: drag view

Richard Bair richard.bair at oracle.com
Mon Jan 14 11:09:22 PST 2013

HI Pavel!

Overall great. I don't see why you can't have a getter. The only way to set the drag view is via an API we control so it seems pretty easy to implement the getter as well. You could either have a DragView class which encapsulates the node/image and the offsetX and offsetY, or you could just break it out into three properties on the DragBoard and save yourself the extra class.

I think you should just have an image based dragImage property and dragImageOffsetX and dragImageOffsetY properties. We shouldn't by default put anything in as the drag image, except for a few UI controls. We'll want a ListView, TreeView, TableView, TreeTableView to automatically pre-populate the DragBoard before the onDragDetected code is called, so that those control give you a nice drag image for free but the developer is free to replace it or clear it as they see fit.

The developer could use the synchronous version of snapshot. But I think either snapshot should be fixed to be transparent by default instead of a white fill by default or add another snapshot method which produces a transparent fill by default. Basically:

source.setOnDragDetected(new EventHandler<MouseEvent>() {
    public void handle(MouseEvent event) {
        DragBoard db = source.startDragAndDrop(TransferMode.ANY);

Maybe also have a convenience method on DragBoard:

    db.updateDragImage(node, x, y);

which then just calls the 3 setters as appropriate.


On Jan 13, 2013, at 11:59 PM, Pavel Safrata <pavel.safrata at oracle.com> wrote:

> Hello,
> this is a proposal of an API allowing to specify the image floating with mouse cursor during a drag&drop operation.
> Jira: http://javafx-jira.kenai.com/browse/RT-14730
> I propose to add two methods to DragBoard:
> setDragView(Image image, double offsetX, double offsetY)
> setDragView(Node node, double offsetX, double offsetY)
> The first one simply uses the given image for the drag view with the offsetX and offsetY specifying cursor position over the image. The second one renders the given node to an image and uses the result (the coordinates being in the node's local space).
> The typical usage will look like this:
>        sourceNode.setOnDragDetected(new EventHandler<MouseEvent>() {
>            public void handle(MouseEvent event) {
>                Dragboard db = source.startDragAndDrop(TransferMode.ANY);
>                ClipboardContent content = ...
>                db.setContent(content);
>                db.setDragView(sourceNode, event.getX(), event.getY()); // that's it
>                event.consume();
>            }
>        });
> This API is meant for telling the operating system what visual cues to provide, I don't think it is useful (and I'm not sure it is even possible) to provide getters.
> There is a possibility to provide default drag view - if none of those methods is called, the default drag view would be an image of the drag gesture source. This should work nice most of the times. However, it may cause inconveniences to some existing apps - for instance a text editor node which puts the selected text on the DragBoard - after updating FX the application starts to show the entire editor in the drag view. For this reason I think the default behavior should remain unchanged.
> Thanks,
> Pavel

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