When the user starts a drag-and-drop operation and the sidebar needs
to ask the application for which drag action to perform, then the
sidebar will emit this signal.
The application can evaluate the @context for customary actions, or
it can check the type of the files indicated by @source_file_list against the
possible actions for the destination @dest_file.
The drag action to use must be the return value of the signal handler.
The drag action to use, for example, #GDK_ACTION_COPY
or #GDK_ACTION_MOVE, or 0 if no action is allowed here (i.e. drops
are not allowed in the specified @dest_file).
When the user starts a drag-and-drop operation and the sidebar needs to ask the application for which drag action to perform, then the sidebar will emit this signal.
The application can evaluate the @context for customary actions, or it can check the type of the files indicated by @source_file_list against the possible actions for the destination @dest_file.
The drag action to use must be the return value of the signal handler.