Implement `delay` for `pop` widget :tada:

3 files changed, 50 insertions, 39 deletions

diff --git a/core/src/lib.rs b/core/src/lib.rs
index 03cc0632..e75ef2a7 100644
--- a/core/src/lib.rs
+++ b/core/src/lib.rs
@@ -144,9 +144,9 @@ impl<F, A, B, O> Function<A, B, O> for F
 where
     F: Fn(A, B) -> O,
     Self: Sized,
-    A: Copy,
+    A: Clone,
 {
     fn with(self, prefix: A) -> impl Fn(B) -> O {
-        move |result| self(prefix, result)
+        move |result| self(prefix.clone(), result)
     }
 }
diff --git a/examples/markdown/src/main.rs b/examples/markdown/src/main.rs
index 512d4b44..c6360359 100644
--- a/examples/markdown/src/main.rs
+++ b/examples/markdown/src/main.rs
@@ -3,14 +3,15 @@ mod icon;
 use iced::animation;
 use iced::clipboard;
 use iced::highlighter;
-use iced::task;
 use iced::time::{self, milliseconds, Instant};
 use iced::widget::{
     self, button, center_x, container, horizontal_space, hover, image,
     markdown, pop, right, row, scrollable, text_editor, toggler,
 };
 use iced::window;
-use iced::{Animation, Element, Fill, Font, Subscription, Task, Theme};
+use iced::{
+    Animation, Element, Fill, Font, Function, Subscription, Task, Theme,
+};
 
 use std::collections::HashMap;
 use std::io;
@@ -39,9 +40,7 @@ enum Mode {
 }
 
 enum Image {
-    Loading {
-        _download: task::Handle,
-    },
+    Loading,
     Ready {
         handle: image::Handle,
         fade_in: Animation<bool>,
@@ -89,9 +88,6 @@ impl Markdown {
                 if is_edit {
                     self.content = markdown::Content::parse(&self.raw.text());
                     self.mode = Mode::Preview;
-
-                    let images = self.content.images();
-                    self.images.retain(|url, _image| images.contains(url));
                 }
 
                 Task::none()
@@ -107,27 +103,12 @@ impl Markdown {
                     return Task::none();
                 }
 
-                let (download_image, handle) = Task::future({
-                    let url = url.clone();
-
-                    async move {
-                        // Wait half a second for further editions before attempting download
-                        tokio::time::sleep(milliseconds(500)).await;
-                        download_image(url).await
-                    }
-                })
-                .abortable();
+                let _ = self.images.insert(url.clone(), Image::Loading);
 
-                let _ = self.images.insert(
-                    url.clone(),
-                    Image::Loading {
-                        _download: handle.abort_on_drop(),
-                    },
-                );
-
-                download_image.map(move |result| {
-                    Message::ImageDownloaded(url.clone(), result)
-                })
+                Task::perform(
+                    download_image(url.clone()),
+                    Message::ImageDownloaded.with(url),
+                )
             }
             Message::ImageDownloaded(url, result) => {
                 let _ = self.images.insert(
@@ -286,6 +267,7 @@ impl<'a> markdown::Viewer<'a, Message> for CustomViewer<'a> {
         } else {
             pop(horizontal_space())
                 .key(url.as_str())
+                .delay(milliseconds(500))
                 .on_show(|_size| Message::ImageShown(url.clone()))
                 .into()
         }
diff --git a/widget/src/pop.rs b/widget/src/pop.rs
index 950371ea..d6dd6bb7 100644
--- a/widget/src/pop.rs
+++ b/widget/src/pop.rs
@@ -4,6 +4,7 @@ use crate::core::mouse;
 use crate::core::overlay;
 use crate::core::renderer;
 use crate::core::text;
+use crate::core::time::{Duration, Instant};
 use crate::core::widget;
 use crate::core::widget::tree::{self, Tree};
 use crate::core::window;
@@ -23,6 +24,7 @@ pub struct Pop<'a, Message, Theme = crate::Theme, Renderer = crate::Renderer> {
     on_resize: Option<Box<dyn Fn(Size) -> Message + 'a>>,
     on_hide: Option<Message>,
     anticipate: Pixels,
+    delay: Duration,
 }
 
 impl<'a, Message, Theme, Renderer> Pop<'a, Message, Theme, Renderer>
@@ -41,6 +43,7 @@ where
             on_resize: None,
             on_hide: None,
             anticipate: Pixels::ZERO,
+            delay: Duration::ZERO,
         }
     }
 
@@ -86,11 +89,21 @@ where
         self.anticipate = distance.into();
         self
     }
+
+    /// Sets the amount of time to wait before firing an [`on_show`] or
+    /// [`on_hide`] event; after the content is shown or hidden.
+    ///
+    /// When combined with [`key`], this can be useful to debounce key changes.
+    pub fn delay(mut self, delay: impl Into<Duration>) -> Self {
+        self.delay = delay.into();
+        self
+    }
 }
 
 #[derive(Debug, Clone, Default)]
 struct State {
     has_popped_in: bool,
+    should_notify_at: Option<(bool, Instant)>,
     last_size: Option<Size>,
     last_key: Option<String>,
 }
@@ -128,13 +141,14 @@ where
         shell: &mut Shell<'_, Message>,
         viewport: &Rectangle,
     ) {
-        if let Event::Window(window::Event::RedrawRequested(_)) = &event {
+        if let Event::Window(window::Event::RedrawRequested(now)) = &event {
             let state = tree.state.downcast_mut::<State>();
 
             if state.has_popped_in
                 && state.last_key.as_deref() != self.key.as_deref()
             {
                 state.has_popped_in = false;
+                state.should_notify_at = None;
                 state.last_key =
                     self.key.as_ref().cloned().map(text::Fragment::into_owned);
             }
@@ -157,19 +171,34 @@ where
                             shell.publish(on_resize(size));
                         }
                     }
-                } else if let Some(on_hide) = &self.on_hide {
+                } else if self.on_hide.is_some() {
                     state.has_popped_in = false;
-                    shell.publish(on_hide.clone());
+                    state.should_notify_at = Some((false, *now + self.delay));
                 }
-            } else if let Some(on_show) = &self.on_show {
-                if distance <= self.anticipate.0 {
-                    let size = bounds.size();
+            } else if self.on_show.is_some() && distance <= self.anticipate.0 {
+                let size = bounds.size();
 
-                    state.has_popped_in = true;
-                    state.last_size = Some(size);
+                state.has_popped_in = true;
+                state.should_notify_at = Some((true, *now + self.delay));
+                state.last_size = Some(size);
+            }
 
-                    shell.publish(on_show(size));
+            match &state.should_notify_at {
+                Some((has_popped_in, at)) if at <= now => {
+                    if *has_popped_in {
+                        if let Some(on_show) = &self.on_show {
+                            shell.publish(on_show(layout.bounds().size()));
+                        }
+                    } else if let Some(on_hide) = &self.on_hide {
+                        shell.publish(on_hide.clone());
+                    }
+
+                    state.should_notify_at = None;
+                }
+                Some((_, at)) => {
+                    shell.request_redraw_at(*at);
                 }
+                None => {}
             }
         }