drag and drop of service_items works

src/main.rs

@@ -150,6 +150,7 @@ enum Message {
     AddServiceItem(usize, ServiceItem),
     AddServiceItemDrop(usize),
     AppendServiceItem(ServiceItem),
+    ReorderService(usize, usize),
     SearchFocus,
     Search(String),
     CloseSearch,
@@ -1061,6 +1062,12 @@ impl cosmic::Application for App {
                 self.presenter.update_items(self.service.clone());
                 Task::none()
             }
+            Message::ReorderService(index, target_index) => {
+                let item = self.service.remove(index);
+                self.service.insert(target_index, item);
+                self.presenter.update_items(self.service.clone());
+                Task::none()
+            }
             Message::Search(query) => {
                 self.search_query = query.clone();
                 self.search(query)
@@ -1457,6 +1464,8 @@ where
                         index,
                     )))
                     .on_exit(Message::HoveredServiceItem(None))
+                    .on_double_press(Message::None)
+                    .on_drag(Message::None)
                     .on_press(Message::ChangeServiceItem(index));
                 // let button = button::standard(item.title.clone())
                 //     .leading_icon({
@@ -1522,7 +1531,14 @@ where
                 .center()
                 .width(Length::Fill),
             iced::widget::horizontal_rule(1),
-            column(list).spacing(10),
+            ui::widgets::draggable::column::column(list).spacing(10).on_drag(|event| {
+                match event {
+                    ui::widgets::draggable::DragEvent::Picked { index } => Message::None,
+                    ui::widgets::draggable::DragEvent::Dropped { index, target_index, drop_position } => Message::ReorderService(index, target_index),
+                    ui::widgets::draggable::DragEvent::Canceled { index } => Message::None,
+                }
+            }),
+            // column(list).spacing(10),
             // service::service(&self.service),
             dnd_destination(
                 vertical_space().width(Length::Fill),

src/ui/widgets/draggable/column.rs

@@ -0,0 +1,865 @@
+//! Distribute draggable content vertically.
+// This widget is a modification of the original `Column` widget from [`iced`]
+//
+// [`iced`]: https://github.com/iced-rs/iced
+//
+// Copyright 2019 Héctor Ramón, Iced contributors
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy of
+// this software and associated documentation files (the "Software"), to deal in
+// the Software without restriction, including without limitation the rights to
+// use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+// the Software, and to permit persons to whom the Software is furnished to do so,
+// subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+// FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+// COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+// IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+// CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+use cosmic::iced::advanced::layout::{self, Layout};
+use cosmic::iced::advanced::widget::{tree, Operation, Tree, Widget};
+use cosmic::iced::advanced::{overlay, renderer, Clipboard, Shell};
+use cosmic::iced::alignment::{self, Alignment};
+use cosmic::iced::event::{self, Event};
+use cosmic::iced::{self, mouse, Transformation};
+use cosmic::iced::{
+    Background, Border, Color, Element, Length, Padding, Pixels,
+    Point, Rectangle, Size, Vector,
+};
+use cosmic::Theme;
+
+use super::{Action, DragEvent, DropPosition};
+
+pub fn column<'a, Message, Theme, Renderer>(
+    children: impl IntoIterator<
+        Item = Element<'a, Message, Theme, Renderer>,
+    >,
+) -> Column<'a, Message, Theme, Renderer>
+where
+    Renderer: renderer::Renderer,
+    Theme: Catalog,
+{
+    Column::with_children(children)
+}
+
+const DRAG_DEADBAND_DISTANCE: f32 = 5.0;
+
+/// A container that distributes its contents vertically.
+///
+/// # Example
+/// ```no_run
+/// # mod iced { pub mod widget { pub use iced_widget::*; } }
+/// # pub type State = ();
+/// # pub type Element<'a, Message> = iced_widget::core::Element<'a, Message, iced_widget::Theme, iced_widget::Renderer>;
+/// use iced::widget::{button, column};
+///
+/// #[derive(Debug, Clone)]
+/// enum Message {
+///     // ...
+/// }
+///
+/// fn view(state: &State) -> Element<'_, Message> {
+///     column![
+///         "I am on top!",
+///         button("I am in the center!"),
+///         "I am below.",
+///     ].into()
+/// }
+/// ```
+#[allow(missing_debug_implementations)]
+pub struct Column<
+    'a,
+    Message,
+    Theme = cosmic::Theme,
+    Renderer = iced::Renderer,
+> where
+    Theme: Catalog,
+{
+    spacing: f32,
+    padding: Padding,
+    width: Length,
+    height: Length,
+    max_width: f32,
+    align: Alignment,
+    clip: bool,
+    deadband_zone: f32,
+    children: Vec<Element<'a, Message, Theme, Renderer>>,
+    on_drag: Option<Box<dyn Fn(DragEvent) -> Message + 'a>>,
+    class: Theme::Class<'a>,
+}
+
+impl<'a, Message, Theme, Renderer>
+    Column<'a, Message, Theme, Renderer>
+where
+    Renderer: renderer::Renderer,
+    Theme: Catalog,
+{
+    /// Creates an empty [`Column`].
+    pub fn new() -> Self {
+        Self::from_vec(Vec::new())
+    }
+
+    /// Creates a [`Column`] with the given capacity.
+    pub fn with_capacity(capacity: usize) -> Self {
+        Self::from_vec(Vec::with_capacity(capacity))
+    }
+
+    /// Creates a [`Column`] with the given elements.
+    pub fn with_children(
+        children: impl IntoIterator<
+            Item = Element<'a, Message, Theme, Renderer>,
+        >,
+    ) -> Self {
+        let iterator = children.into_iter();
+
+        Self::with_capacity(iterator.size_hint().0).extend(iterator)
+    }
+
+    /// Creates a [`Column`] from an already allocated [`Vec`].
+    ///
+    /// Keep in mind that the [`Column`] will not inspect the [`Vec`], which means
+    /// it won't automatically adapt to the sizing strategy of its contents.
+    ///
+    /// If any of the children have a [`Length::Fill`] strategy, you will need to
+    /// call [`Column::width`] or [`Column::height`] accordingly.
+    pub fn from_vec(
+        children: Vec<Element<'a, Message, Theme, Renderer>>,
+    ) -> Self {
+        Self {
+            spacing: 0.0,
+            padding: Padding::ZERO,
+            width: Length::Shrink,
+            height: Length::Shrink,
+            max_width: f32::INFINITY,
+            align: Alignment::Start,
+            clip: false,
+            deadband_zone: DRAG_DEADBAND_DISTANCE,
+            children,
+            class: Theme::default(),
+            on_drag: None,
+        }
+    }
+
+    /// Sets the vertical spacing _between_ elements.
+    ///
+    /// Custom margins per element do not exist in iced. You should use this
+    /// method instead! While less flexible, it helps you keep spacing between
+    /// elements consistent.
+    pub fn spacing(mut self, amount: impl Into<Pixels>) -> Self {
+        self.spacing = amount.into().0;
+        self
+    }
+
+    /// Sets the [`Padding`] of the [`Column`].
+    pub fn padding<P: Into<Padding>>(mut self, padding: P) -> Self {
+        self.padding = padding.into();
+        self
+    }
+
+    /// Sets the width of the [`Column`].
+    pub fn width(mut self, width: impl Into<Length>) -> Self {
+        self.width = width.into();
+        self
+    }
+
+    /// Sets the height of the [`Column`].
+    pub fn height(mut self, height: impl Into<Length>) -> Self {
+        self.height = height.into();
+        self
+    }
+
+    /// Sets the maximum width of the [`Column`].
+    pub fn max_width(mut self, max_width: impl Into<Pixels>) -> Self {
+        self.max_width = max_width.into().0;
+        self
+    }
+
+    /// Sets the horizontal alignment of the contents of the [`Column`] .
+    pub fn align_x(
+        mut self,
+        align: impl Into<alignment::Horizontal>,
+    ) -> Self {
+        self.align = Alignment::from(align.into());
+        self
+    }
+
+    /// Sets whether the contents of the [`Column`] should be clipped on
+    /// overflow.
+    pub fn clip(mut self, clip: bool) -> Self {
+        self.clip = clip;
+        self
+    }
+
+    /// Sets the drag deadband zone of the [`Column`].
+    pub fn deadband_zone(mut self, deadband_zone: f32) -> Self {
+        self.deadband_zone = deadband_zone;
+        self
+    }
+
+    /// Adds an element to the [`Column`].
+    pub fn push(
+        mut self,
+        child: impl Into<Element<'a, Message, Theme, Renderer>>,
+    ) -> Self {
+        let child = child.into();
+        let child_size = child.as_widget().size_hint();
+
+        self.width = self.width.enclose(child_size.width);
+        self.height = self.height.enclose(child_size.height);
+
+        self.children.push(child);
+        self
+    }
+
+    /// Adds an element to the [`Column`], if `Some`.
+    pub fn push_maybe(
+        self,
+        child: Option<
+            impl Into<Element<'a, Message, Theme, Renderer>>,
+        >,
+    ) -> Self {
+        if let Some(child) = child {
+            self.push(child)
+        } else {
+            self
+        }
+    }
+
+    /// Sets the style of the [`Column`].
+    #[must_use]
+    pub fn style(
+        mut self,
+        style: impl Fn(&Theme) -> Style + 'a,
+    ) -> Self
+    where
+        Theme::Class<'a>: From<StyleFn<'a, Theme>>,
+    {
+        self.class = (Box::new(style) as StyleFn<'a, Theme>).into();
+        self
+    }
+
+    /// Sets the style class of the [`Column`].
+    #[must_use]
+    pub fn class(
+        mut self,
+        class: impl Into<Theme::Class<'a>>,
+    ) -> Self {
+        self.class = class.into();
+        self
+    }
+
+    /// Extends the [`Column`] with the given children.
+    pub fn extend(
+        self,
+        children: impl IntoIterator<
+            Item = Element<'a, Message, Theme, Renderer>,
+        >,
+    ) -> Self {
+        children.into_iter().fold(self, Self::push)
+    }
+
+    /// The message produced by the [`Column`] when a child is dragged.
+    pub fn on_drag(
+        mut self,
+        on_reorder: impl Fn(DragEvent) -> Message + 'a,
+    ) -> Self {
+        self.on_drag = Some(Box::new(on_reorder));
+        self
+    }
+
+    // Computes the index and position where a dragged item should be dropped.
+    fn compute_target_index(
+        &self,
+        cursor_position: Point,
+        layout: Layout<'_>,
+        dragged_index: usize,
+    ) -> (usize, DropPosition) {
+        let cursor_y = cursor_position.y;
+
+        for (i, child_layout) in layout.children().enumerate() {
+            let bounds = child_layout.bounds();
+            let y = bounds.y;
+            let height = bounds.height;
+
+            if cursor_y >= y && cursor_y <= y + height {
+                if i == dragged_index {
+                    // Cursor is over the dragged item itself
+                    return (i, DropPosition::Swap);
+                }
+
+                let thickness = height / 4.0;
+                let top_threshold = y + thickness;
+                let bottom_threshold = y + height - thickness;
+
+                if cursor_y < top_threshold {
+                    // Near the top edge - insert above
+                    return (i, DropPosition::Before);
+                } else if cursor_y > bottom_threshold {
+                    // Near the bottom edge - insert below
+                    return (i + 1, DropPosition::After);
+                } else {
+                    // Middle area - swap
+                    return (i, DropPosition::Swap);
+                }
+            } else if cursor_y < y {
+                // Cursor is above this child
+                return (i, DropPosition::Before);
+            }
+        }
+
+        // Cursor is below all children
+        (self.children.len(), DropPosition::After)
+    }
+}
+
+impl<'a, Message, Renderer> Default
+    for Column<'a, Message, Theme, Renderer>
+where
+    Renderer: renderer::Renderer,
+    Theme: Catalog,
+{
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<'a, Message, Theme, Renderer: renderer::Renderer>
+    FromIterator<Element<'a, Message, Theme, Renderer>>
+    for Column<'a, Message, Theme, Renderer>
+where
+    Theme: Catalog,
+{
+    fn from_iter<
+        T: IntoIterator<Item = Element<'a, Message, Theme, Renderer>>,
+    >(
+        iter: T,
+    ) -> Self {
+        Self::with_children(iter)
+    }
+}
+
+impl<'a, Message, Theme, Renderer> Widget<Message, Theme, Renderer>
+    for Column<'a, Message, Theme, Renderer>
+where
+    Renderer: renderer::Renderer,
+    Theme: Catalog,
+{
+    fn tag(&self) -> tree::Tag {
+        tree::Tag::of::<Action>()
+    }
+
+    fn state(&self) -> tree::State {
+        tree::State::new(Action::Idle)
+    }
+
+    fn children(&self) -> Vec<Tree> {
+        self.children.iter().map(Tree::new).collect()
+    }
+
+    fn diff(&mut self, tree: &mut Tree) {
+        tree.diff_children(&mut self.children);
+    }
+
+    fn size(&self) -> Size<Length> {
+        Size {
+            width: self.width,
+            height: self.height,
+        }
+    }
+
+    fn layout(
+        &self,
+        tree: &mut Tree,
+        renderer: &Renderer,
+        limits: &layout::Limits,
+    ) -> layout::Node {
+        let limits = limits.max_width(self.max_width);
+
+        layout::flex::resolve(
+            layout::flex::Axis::Vertical,
+            renderer,
+            &limits,
+            self.width,
+            self.height,
+            self.padding,
+            self.spacing,
+            self.align,
+            &self.children,
+            &mut tree.children,
+        )
+    }
+
+    fn operate(
+        &self,
+        tree: &mut Tree,
+        layout: Layout<'_>,
+        renderer: &Renderer,
+        operation: &mut dyn Operation,
+    ) {
+        operation.container(
+            None,
+            layout.bounds(),
+            &mut |operation| {
+                self.children
+                    .iter()
+                    .zip(&mut tree.children)
+                    .zip(layout.children())
+                    .for_each(|((child, state), layout)| {
+                        child.as_widget().operate(
+                            state, layout, renderer, operation,
+                        );
+                    });
+            },
+        );
+    }
+
+    fn on_event(
+        &mut self,
+        tree: &mut Tree,
+        event: Event,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        renderer: &Renderer,
+        clipboard: &mut dyn Clipboard,
+        shell: &mut Shell<'_, Message>,
+        viewport: &Rectangle,
+    ) -> event::Status {
+        let mut event_status = event::Status::Ignored;
+
+        let action = tree.state.downcast_mut::<Action>();
+
+        match event {
+            Event::Mouse(mouse::Event::ButtonPressed(
+                mouse::Button::Left,
+            )) => {
+                if let Some(cursor_position) =
+                    cursor.position_over(layout.bounds())
+                {
+                    for (index, child_layout) in
+                        layout.children().enumerate()
+                    {
+                        if child_layout
+                            .bounds()
+                            .contains(cursor_position)
+                        {
+                            *action = Action::Picking {
+                                index,
+                                origin: cursor_position,
+                            };
+                            event_status = event::Status::Captured;
+                            break;
+                        }
+                    }
+                }
+            }
+            Event::Mouse(mouse::Event::CursorMoved { .. }) => {
+                match *action {
+                    Action::Picking { index, origin } => {
+                        if let Some(cursor_position) =
+                            cursor.position()
+                        {
+                            if cursor_position.distance(origin)
+                                > self.deadband_zone
+                            {
+                                // Start dragging
+                                *action = Action::Dragging {
+                                    index,
+                                    origin,
+                                    last_cursor: cursor_position,
+                                };
+                                if let Some(on_reorder) =
+                                    &self.on_drag
+                                {
+                                    shell.publish(on_reorder(
+                                        DragEvent::Picked { index },
+                                    ));
+                                }
+                                event_status =
+                                    event::Status::Captured;
+                            }
+                        }
+                    }
+                    Action::Dragging { origin, index, .. } => {
+                        if let Some(cursor_position) =
+                            cursor.position()
+                        {
+                            *action = Action::Dragging {
+                                last_cursor: cursor_position,
+                                origin,
+                                index,
+                            };
+                            event_status = event::Status::Captured;
+                        }
+                    }
+                    _ => {}
+                }
+            }
+            Event::Mouse(mouse::Event::ButtonReleased(
+                mouse::Button::Left,
+            )) => {
+                match *action {
+                    Action::Dragging { index, .. } => {
+                        if let Some(cursor_position) =
+                            cursor.position()
+                        {
+                            let bounds = layout.bounds();
+                            if bounds.contains(cursor_position) {
+                                let (target_index, drop_position) =
+                                    self.compute_target_index(
+                                        cursor_position,
+                                        layout,
+                                        index,
+                                    );
+
+                                if let Some(on_reorder) =
+                                    &self.on_drag
+                                {
+                                    shell.publish(on_reorder(
+                                        DragEvent::Dropped {
+                                            index,
+                                            target_index,
+                                            drop_position,
+                                        },
+                                    ));
+                                    event_status =
+                                        event::Status::Captured;
+                                }
+                            } else if let Some(on_reorder) =
+                                &self.on_drag
+                            {
+                                shell.publish(on_reorder(
+                                    DragEvent::Canceled { index },
+                                ));
+                                event_status =
+                                    event::Status::Captured;
+                            }
+                        }
+                        *action = Action::Idle;
+                    }
+                    Action::Picking { .. } => {
+                        // Did not move enough to start dragging
+                        *action = Action::Idle;
+                    }
+                    _ => {}
+                }
+            }
+            _ => {}
+        }
+
+        let child_status = self
+            .children
+            .iter_mut()
+            .zip(&mut tree.children)
+            .zip(layout.children())
+            .map(|((child, state), layout)| {
+                child.as_widget_mut().on_event(
+                    state,
+                    event.clone(),
+                    layout,
+                    cursor,
+                    renderer,
+                    clipboard,
+                    shell,
+                    viewport,
+                )
+            })
+            .fold(event::Status::Ignored, event::Status::merge);
+
+        event::Status::merge(event_status, child_status)
+    }
+
+    fn mouse_interaction(
+        &self,
+        tree: &Tree,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        viewport: &Rectangle,
+        renderer: &Renderer,
+    ) -> mouse::Interaction {
+        let action = tree.state.downcast_ref::<Action>();
+
+        if let Action::Dragging { .. } = *action {
+            return mouse::Interaction::Grabbing;
+        }
+
+        self.children
+            .iter()
+            .zip(&tree.children)
+            .zip(layout.children())
+            .map(|((child, state), layout)| {
+                child.as_widget().mouse_interaction(
+                    state, layout, cursor, viewport, renderer,
+                )
+            })
+            .max()
+            .unwrap_or_default()
+    }
+
+    fn draw(
+        &self,
+        tree: &Tree,
+        renderer: &mut Renderer,
+        theme: &Theme,
+        defaults: &renderer::Style,
+        layout: Layout<'_>,
+        cursor: mouse::Cursor,
+        viewport: &Rectangle,
+    ) {
+        let action = tree.state.downcast_ref::<Action>();
+        let style = theme.style(&self.class);
+
+        match action {
+            Action::Dragging {
+                index,
+                last_cursor,
+                origin,
+                ..
+            } => {
+                let child_count = self.children.len();
+
+                // Determine the target index based on cursor position
+                let target_index = if cursor.position().is_some() {
+                    let (target_index, _) = self
+                        .compute_target_index(
+                            *last_cursor,
+                            layout,
+                            *index,
+                        );
+                    target_index.min(child_count - 1)
+                } else {
+                    *index
+                };
+
+                // Store the width of the dragged item
+                let drag_bounds =
+                    layout.children().nth(*index).unwrap().bounds();
+                let drag_height = drag_bounds.height + self.spacing;
+
+                // Draw all children except the one being dragged
+                let mut translations = 0.0;
+                for i in 0..child_count {
+                    let child = &self.children[i];
+                    let state = &tree.children[i];
+                    let child_layout =
+                        layout.children().nth(i).unwrap();
+
+                    // Draw the dragged item separately
+                    // TODO: Draw a shadow below the picked item to enhance the
+                    // floating effect
+                    if i == *index {
+                        let scaling =
+                            Transformation::scale(style.scale);
+                        let translation =
+                            *last_cursor - *origin * scaling;
+                        renderer.with_translation(
+                            translation,
+                            |renderer| {
+                                renderer.with_transformation(
+                                    scaling,
+                                    |renderer| {
+                                        renderer.with_layer(
+                                            child_layout.bounds(),
+                                            |renderer| {
+                                                child
+                                                    .as_widget()
+                                                    .draw(
+                                                        state,
+                                                        renderer,
+                                                        theme,
+                                                        defaults,
+                                                        child_layout,
+                                                        cursor,
+                                                        viewport,
+                                                    );
+                                            },
+                                        );
+                                    },
+                                );
+                            },
+                        );
+                    } else {
+                        let offset: i32 =
+                            match target_index.cmp(index) {
+                                std::cmp::Ordering::Less
+                                    if i >= target_index
+                                        && i < *index =>
+                                {
+                                    1
+                                }
+                                std::cmp::Ordering::Greater
+                                    if i > *index
+                                        && i <= target_index =>
+                                {
+                                    -1
+                                }
+                                _ => 0,
+                            };
+
+                        let translation = Vector::new(
+                            0.0,
+                            offset as f32 * drag_height,
+                        );
+                        renderer.with_translation(
+                            translation,
+                            |renderer| {
+                                child.as_widget().draw(
+                                    state,
+                                    renderer,
+                                    theme,
+                                    defaults,
+                                    child_layout,
+                                    cursor,
+                                    viewport,
+                                );
+                                // Draw an overlay if this item is being moved
+                                // TODO: instead of drawing an overlay, it would be nicer to
+                                // draw the item with a reduced opacity, but that's not possible today
+                                if offset != 0 {
+                                    renderer.fill_quad(
+                                        renderer::Quad {
+                                            bounds: child_layout
+                                                .bounds(),
+                                            ..renderer::Quad::default(
+                                            )
+                                        },
+                                        style.moved_item_overlay,
+                                    );
+
+                                    // Keep track of the total translation so we can
+                                    // draw the "ghost" of the dragged item later
+                                    translations -= (child_layout
+                                        .bounds()
+                                        .height
+                                        + self.spacing)
+                                        * offset.signum() as f32;
+                                }
+                            },
+                        );
+                    }
+                }
+                // Draw a ghost of the dragged item in its would-be position
+                let ghost_translation =
+                    Vector::new(0.0, translations);
+                renderer.with_translation(
+                    ghost_translation,
+                    |renderer| {
+                        renderer.fill_quad(
+                            renderer::Quad {
+                                bounds: drag_bounds,
+                                border: style.ghost_border,
+                                ..renderer::Quad::default()
+                            },
+                            style.ghost_background,
+                        );
+                    },
+                );
+            }
+            _ => {
+                // Draw all children normally when not dragging
+                for ((child, state), layout) in self
+                    .children
+                    .iter()
+                    .zip(&tree.children)
+                    .zip(layout.children())
+                {
+                    child.as_widget().draw(
+                        state, renderer, theme, defaults, layout,
+                        cursor, viewport,
+                    );
+                }
+            }
+        }
+    }
+
+    fn overlay<'b>(
+        &'b mut self,
+        tree: &'b mut Tree,
+        layout: Layout<'_>,
+        renderer: &Renderer,
+        translation: Vector,
+    ) -> Option<overlay::Element<'b, Message, Theme, Renderer>> {
+        overlay::from_children(
+            &mut self.children,
+            tree,
+            layout,
+            renderer,
+            translation,
+        )
+    }
+}
+
+impl<'a, Message, Theme, Renderer>
+    From<Column<'a, Message, Theme, Renderer>>
+    for Element<'a, Message, Theme, Renderer>
+where
+    Message: 'a,
+    Theme: Catalog + 'a,
+    Renderer: renderer::Renderer + 'a,
+{
+    fn from(column: Column<'a, Message, Theme, Renderer>) -> Self {
+        Self::new(column)
+    }
+}
+
+/// The theme catalog of a [`Column`].
+pub trait Catalog {
+    /// The item class of the [`Catalog`].
+    type Class<'a>;
+
+    /// The default class produced by the [`Catalog`].
+    fn default<'a>() -> Self::Class<'a>;
+
+    /// The [`Style`] of a class with the given status.
+    fn style(&self, class: &Self::Class<'_>) -> Style;
+}
+
+/// The appearance of a [`Column`].
+#[derive(Debug, Clone, Copy)]
+pub struct Style {
+    /// The scaling to apply to a picked element while it's being dragged.
+    pub scale: f32,
+    /// The color of the overlay on items that are moved around
+    pub moved_item_overlay: Color,
+    /// The outline border of the dragged item's ghost
+    pub ghost_border: Border,
+    /// The background of the dragged item's ghost
+    pub ghost_background: Background,
+}
+
+/// A styling function for a [`Column`].
+pub type StyleFn<'a, Theme> = Box<dyn Fn(&Theme) -> Style + 'a>;
+
+impl Catalog for cosmic::Theme {
+    type Class<'a> = StyleFn<'a, Self>;
+
+    fn default<'a>() -> Self::Class<'a> {
+        Box::new(default)
+    }
+
+    fn style(&self, class: &Self::Class<'_>) -> Style {
+        class(self)
+    }
+}
+
+pub fn default(theme: &Theme) -> Style {
+    Style {
+        scale: 1.05,
+        moved_item_overlay: Color::from(theme.cosmic().primary.base)
+            .scale_alpha(0.2)
+            .into(),
+        ghost_border: Border {
+            width: 1.0,
+            color: theme.cosmic().secondary.base.into(),
+            radius: 0.0.into(),
+        },
+        ghost_background: Color::from(theme.cosmic().secondary.base)
+            .scale_alpha(0.2)
+            .into(),
+    }
+}

src/ui/widgets/draggable/mod.rs

@@ -0,0 +1,42 @@
+use cosmic::iced::Point;
+
+pub use self::column::column;
+pub use self::row::row;
+pub mod column;
+pub mod row;
+
+#[derive(Debug, Clone)]
+pub enum Action {
+    Idle,
+    Picking {
+        index: usize,
+        origin: Point,
+    },
+    Dragging {
+        index: usize,
+        origin: Point,
+        last_cursor: Point,
+    },
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum DropPosition {
+    Before,
+    Swap,
+    After,
+}
+
+#[derive(Debug, Clone)]
+pub enum DragEvent {
+    Picked {
+        index: usize,
+    },
+    Dropped {
+        index: usize,
+        target_index: usize,
+        drop_position: DropPosition,
+    },
+    Canceled {
+        index: usize,
+    },
+}

src/ui/widgets/mod.rs

@@ -1 +1,2 @@
 // pub mod slide_text;
+pub mod draggable;