Drag and Drop works ok now.

The main functionality works but only in cosmic desktop. So there are
some issues that need to be worked out yet in regards to libcosmic.

src/main.rs

@@ -15,7 +15,8 @@ use cosmic::widget::nav_bar::nav_bar_style;
 use cosmic::widget::segmented_button::Entity;
 use cosmic::widget::tooltip::Position as TPosition;
 use cosmic::widget::{
-    button, nav_bar, text, tooltip, DndSource, Id, Space,
+    button, nav_bar, text, tooltip, DndDestination, DndSource, Id,
+    Space,
 };
 use cosmic::widget::{icon, slider};
 use cosmic::{executor, Application, ApplicationExt, Element};
@@ -28,6 +29,7 @@ use std::path::PathBuf;
 use tracing::{debug, level_filters::LevelFilter};
 use tracing::{error, warn};
 use tracing_subscriber::EnvFilter;
+use ui::editor::SongEditor;
 use ui::library::{self, Library};
 
 pub mod core;
@@ -96,12 +98,14 @@ struct App {
     library: Option<Library>,
     library_open: bool,
     library_width: f32,
+    song_editor: SongEditor,
 }
 
 #[derive(Debug, Clone)]
 enum Message {
     Present(presenter::Message),
     Library(library::Message),
+    SongEditor(editor::Message),
     File(PathBuf),
     DndEnter(Entity, Vec<String>),
     DndDrop(Entity, Option<ServiceItem>, DndAction),
@@ -165,6 +169,7 @@ impl cosmic::Application for App {
         let presenter = Presenter::with_items(items.clone());
         let slides = items.to_slides().unwrap_or_default();
         let current_slide = slides[0].clone();
+        let song_editor = SongEditor::new();
 
         for item in items.iter() {
             nav_model.insert().text(item.title()).data(item.clone());
@@ -174,6 +179,7 @@ impl cosmic::Application for App {
 
         let mut app = App {
             presenter,
+            song_editor,
             core,
             nav_model,
             file: PathBuf::default(),
@@ -221,15 +227,12 @@ impl cosmic::Application for App {
                 cosmic::app::cosmic::Message::NavBar(id),
             )
         })
-        .on_dnd_drop(|entity, data, action| {
-            cosmic::app::Message::App(Message::DndDrop(
-                entity, data, action,
-            ))
-        })
         .on_dnd_enter(|entity, data| {
+            debug!("entered");
             cosmic::app::Message::App(Message::DndEnter(entity, data))
         })
         .on_dnd_leave(|entity| {
+            debug!("left");
             cosmic::app::Message::App(Message::DndLeave(entity))
         })
         .drag_id(DragId::new())
@@ -238,6 +241,12 @@ impl cosmic::Application for App {
                 cosmic::app::cosmic::Message::NavBarContext(id),
             )
         })
+        .on_dnd_drop::<ServiceItem>(|entity, data, action| {
+            debug!("dropped");
+            cosmic::app::Message::App(Message::DndDrop(
+                entity, data, action,
+            ))
+        })
         .context_menu(None)
         .into_container()
         // XXX both must be shrink to avoid flex layout from ignoring it
@@ -248,6 +257,14 @@ impl cosmic::Application for App {
             nav = nav.max_width(280);
         }
 
+        // let dnd = DndDestination::new(
+        //     nav,
+        //     vec!["application/service-item".to_string().into()],
+        // )
+        // .data_received_for(|item| {
+        //     cosmic::app::Message::App(Message::DndDrop(item))
+        // });
+
         let column = column![
             text::heading("Service List").center().width(280),
             nav
@@ -423,6 +440,9 @@ impl cosmic::Application for App {
                     _ => Task::none(),
                 }
             }
+            Message::SongEditor(message) => {
+                todo!()
+            }
             Message::Present(message) => {
                 // debug!(?message);
                 if self.presentation_open {
@@ -523,8 +543,8 @@ impl cosmic::Application for App {
             }
             Message::DndDrop(entity, service_item, action) => {
                 debug!(?entity);
-                debug!(?service_item);
                 debug!(?action);
+                debug!(?service_item);
                 Task::none()
             }
             Message::AddLibrary(library) => {
@@ -614,6 +634,9 @@ impl cosmic::Application for App {
             })
             .style(nav_bar_style)
             .center(Length::Fill);
+
+        let song_editor =
+            self.song_editor.view().map(|m| Message::SongEditor(m));
         // let dnd_source: DndSource<Message, _> = DndSource::with_id(
         //     drag_item.expect("errors").map(|m| Message::Library(m)),
         //     Id::new("item"),