Bevy Version: | 0.14 | (outdated!) |
---|
As this page is outdated, please refer to Bevy's official migration guides while reading, to cover the differences: 0.14 to 0.15.
I apologize for the inconvenience. I will update the page as soon as I find the time.
Drag-and-Drop (Files)
Relevant official examples:
drag_and_drop
.
Bevy supports the Drag-and-Drop gesture common on most desktop operating systems, but only for files, not arbitrary data / objects.
If you drag a file (say, from the file manager app) into a Bevy app, Bevy
will produce a FileDragAndDrop
event, containing the path
of the file that was dropped in.
fn file_drop(
mut evr_dnd: EventReader<FileDragAndDrop>,
) {
for ev in evr_dnd.read() {
if let FileDragAndDrop::DroppedFile { window, path_buf } = ev {
println!("Dropped file with path: {:?}, in window id: {:?}", path_buf, window);
}
}
}
Detecting the Position of the Drop
You may want to do different things depending on where the cursor was when the drop gesture ended. For example, add the file to some collection, if it was dropped over a specific UI element/panel.
Unfortunately, this is currently somewhat tricky to implement, due to winit
bug #1550. Bevy does not get CursorMoved
events
while the drag gesture is ongoing, and therefore does not respond to the
mouse cursor. Bevy completely loses track of the cursor position.
Checking the cursor position from the Window
will also not work.
Systems that use cursor events to respond to cursor movements will not work
during a drag gesture. This includes Bevy UI's Interaction
detection,
which is the usual way of detecting when a UI element is hovered over.
Workaround
The only way to workaround this issue is to store the file path somewhere
temporarily after receiving the drop event. Then, wait until the next
CursorMoved
event, and then process the file.
Note that this might not even be on the next frame update. The next cursor update will happen whenever the user moves the cursor. If the user does not immediately move the mouse after dropping the file and leaves the cursor in the same place for a while, there will be no events and your app will have no way of knowing the cursor position.