IDropAction

Properties

Base	number	write
Effect	number	read, write
Playlist	number	write
ToSelect	boolean	write

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://docs.microsoft.com/en-gb/windows/win32/com/dropeffect-constants

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:

Example

function on_drag_over(action, x, y, mask) {
    var ap = plman.ActivePlaylist;
    if (plman.PlaylistCount == 0 || ap == -1) {
        // no playlists or active playlist not set
        action.Effect = 0;
    } else if (plman.IsAutoPlaylist(ap)) {
        // autoplaylist, can't drop.
        action.Effect = 0;
    } else {
        // ok, we can drop here.
        action.Effect = 1;
    }
}

Note

The example above does not take in to account playlist locks that prevent the addition of items to playlists that are not autoplaylists. You can read more about that here.

When it comes to handling the dropped files inside on_drag_drop, we make use of the Base, Playlist and ToSelect properties listed above.

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.

Example

function on_drag_drop(action, x, y, mask) {
    var ap = plman.ActivePlaylist;
    if (plman.PlaylistCount == 0 || ap == -1) {
        // no playlists or active playlist not set
        action.Effect = 0;
    } else if (plman.IsAutoPlaylist(ap)) {
        // autoplaylist, can't drop.
        action.Effect = 0;
    } else {
        // use extra properties here
        action.Playlist = ap;
        // append to end
        action.Base = plman.GetPlaylistItemCount(ap);
        action.ToSelect = true;
        action.Effect = 1;
    }
}