Drag and Drop

• This is a topic for advanced users who are capable of writing their own playlist/library viewers!

Incoming

To handle incoming files from other panels or Windows Explorer, there are 4 callbacks.

function on_drag_drop(action, x, y, mask) {}
function on_drag_enter(action, x, y, mask) {}
function on_drag_leave() {}
function on_drag_over(action, x, y, mask) {}

First we’ll look at the action.Effect property which is documented here.

https://msdn.microsoft.com/en-us/library/windows/desktop/ms693457.aspx

• Rather than set variables for DROPEFFECT_NONE and DROPEFFECT_COPY, I’ll just use 0 and 1 in the examples below.

When used inside the on_drag_over callback, it can be used to provide feedback to the user as to whether you can drop files there or not. If you set the value to 0, the mouse pointer will change to show that dropping files is prohibited. To show that dropping files is allowed, we would use the value of 1.

If you had a playlist viewer script, usage could be as simple as this:

function on_drag_over(action, x, y, mask) {
	if (plman.PlaylistCount == 0) {
		// no playlists, can't drop.
		action.Effect = 0;
	} else if (plman.IsPlaylistLocked(plman.ActivePlaylist)) {
		// autoplaylist or playlist is set to read-only with foo_utils, can't drop.
		action.Effect = 0;
	} else {
		// ok, we can drop here.
		action.Effect = 1;
	}
}

When it comes to handling the dropped files inside on_drag_drop, there are 3 extra properties we need to use:

• Playlist number
• Base number
• ToSelect boolean (if true, select files and set focus to first new file)

We can use the exact same logic as before to set action.Effect as we need to do this so the source of our files gets notified of our intent. We should only ever use values of 0 or 1.

function on_drag_drop(action, x, y, mask) {
	if (plman.PlaylistCount == 0) {
		// no playlists, can't drop.
		action.Effect = 0;
	} else if (plman.IsPlaylistLocked(plman.ActivePlaylist)) {
 		// autoplaylist or playlist is set to read-only with foo_utils, can't drop.
		action.Effect = 0;
	} else {
		// use extra properties here
		action.Playlist = plman.ActivePlaylist;
		 // append to end
		action.Base = plman.PlaylistItemCount(plman.ActivePlaylist);
		action.ToSelect = true;
		action.Effect = 1;
	}
}

Outgoing

• Sorry if this is vague but I barely understand the basic concepts myself and don’t have much clue when it comes to working examples!

There is a new fb.DoDragDrop method which allows you to drag a handle list to external panels/Windows Explorer. It takes 2 arguments: a handle list and allowed effect. It also returns effect which notifies you what the destination did with the files.

Your mouse button should be down when calling the method but you typically won’t do it inside the on_mouse_lbtn_down callback - you might call it inside on_mouse_move when you know the mouse button is down and the mouse has moved a certain distance from the original click point.

var items = plman.GetPlaylistSelectedItems(plman.ActivePlaylist);
// effects can be combined
var effect = fb.DoDragDrop(items, 0|1);
// nothing happens here until the mouse button is released
items.Dispose();

If your script is a library viewer with no incoming files support, you really don’t need to know or care about the returned effect - it’s entirely up to the destination to handle the dropped files.

Things can be more complicated if you have a playlist viewer and you’re not sure if you’re doing to be dropping the files externally or within your own panel to move a selection within a playlist. For now, check this comment…

https://github.com/marc2k3/foo_jscript_panel/pull/19#issuecomment-371827355