Merge pull request #2287 from iced-rs/assert-scrollable-content

Assert `scrollable` content size never fills scrolling axis

examples/scrollable/src/main.rs

@@ -2,7 +2,7 @@ use iced::executor;
 use iced::widget::scrollable::Properties;
 use iced::widget::{
     button, column, container, horizontal_space, progress_bar, radio, row,
-    scrollable, slider, text, vertical_space,
+    scrollable, slider, text, vertical_space, Scrollable,
 };
 use iced::{
     Alignment, Application, Color, Command, Element, Length, Settings, Theme,
@@ -212,7 +212,7 @@ impl Application for ScrollableDemo {
 
         let scrollable_content: Element<Message> =
             Element::from(match self.scrollable_direction {
-                Direction::Vertical => scrollable(
+                Direction::Vertical => Scrollable::with_direction(
                     column![
                         scroll_to_end_button(),
                         text("Beginning!"),
@@ -225,19 +225,19 @@ impl Application for ScrollableDemo {
                     .align_items(Alignment::Center)
                     .padding([40, 0, 40, 0])
                     .spacing(40),
+                    scrollable::Direction::Vertical(
+                        Properties::new()
+                            .width(self.scrollbar_width)
+                            .margin(self.scrollbar_margin)
+                            .scroller_width(self.scroller_width)
+                            .alignment(self.alignment),
+                    ),
                 )
                 .width(Length::Fill)
                 .height(Length::Fill)
-                .direction(scrollable::Direction::Vertical(
-                    Properties::new()
-                        .width(self.scrollbar_width)
-                        .margin(self.scrollbar_margin)
-                        .scroller_width(self.scroller_width)
-                        .alignment(self.alignment),
-                ))
                 .id(SCROLLABLE_ID.clone())
                 .on_scroll(Message::Scrolled),
-                Direction::Horizontal => scrollable(
+                Direction::Horizontal => Scrollable::with_direction(
                     row![
                         scroll_to_end_button(),
                         text("Beginning!"),
@@ -251,19 +251,19 @@ impl Application for ScrollableDemo {
                     .align_items(Alignment::Center)
                     .padding([0, 40, 0, 40])
                     .spacing(40),
+                    scrollable::Direction::Horizontal(
+                        Properties::new()
+                            .width(self.scrollbar_width)
+                            .margin(self.scrollbar_margin)
+                            .scroller_width(self.scroller_width)
+                            .alignment(self.alignment),
+                    ),
                 )
                 .width(Length::Fill)
                 .height(Length::Fill)
-                .direction(scrollable::Direction::Horizontal(
-                    Properties::new()
-                        .width(self.scrollbar_width)
-                        .margin(self.scrollbar_margin)
-                        .scroller_width(self.scroller_width)
-                        .alignment(self.alignment),
-                ))
                 .id(SCROLLABLE_ID.clone())
                 .on_scroll(Message::Scrolled),
-                Direction::Multi => scrollable(
+                Direction::Multi => Scrollable::with_direction(
                     //horizontal content
                     row![
                         column![
@@ -293,21 +293,21 @@ impl Application for ScrollableDemo {
                     .align_items(Alignment::Center)
                     .padding([0, 40, 0, 40])
                     .spacing(40),
+                    {
+                        let properties = Properties::new()
+                            .width(self.scrollbar_width)
+                            .margin(self.scrollbar_margin)
+                            .scroller_width(self.scroller_width)
+                            .alignment(self.alignment);
+
+                        scrollable::Direction::Both {
+                            horizontal: properties,
+                            vertical: properties,
+                        }
+                    },
                 )
                 .width(Length::Fill)
                 .height(Length::Fill)
-                .direction({
-                    let properties = Properties::new()
-                        .width(self.scrollbar_width)
-                        .margin(self.scrollbar_margin)
-                        .scroller_width(self.scroller_width)
-                        .alignment(self.alignment);
-
-                    scrollable::Direction::Both {
-                        horizontal: properties,
-                        vertical: properties,
-                    }
-                })
                 .id(SCROLLABLE_ID.clone())
                 .on_scroll(Message::Scrolled),
             });

widget/src/scrollable.rs

@@ -47,16 +47,38 @@ where
     Theme: StyleSheet,
     Renderer: crate::core::Renderer,
 {
-    /// Creates a new [`Scrollable`].
+    /// Creates a new vertical [`Scrollable`].
     pub fn new(
         content: impl Into<Element<'a, Message, Theme, Renderer>>,
     ) -> Self {
+        Self::with_direction(content, Direction::default())
+    }
+
+    /// Creates a new [`Scrollable`] with the given [`Direction`].
+    pub fn with_direction(
+        content: impl Into<Element<'a, Message, Theme, Renderer>>,
+        direction: Direction,
+    ) -> Self {
+        let content = content.into();
+
+        debug_assert!(
+            direction.vertical().is_none()
+                || !content.as_widget().size_hint().height.is_fill(),
+            "scrollable content must not fill its vertical scrolling axis"
+        );
+
+        debug_assert!(
+            direction.horizontal().is_none()
+                || !content.as_widget().size_hint().width.is_fill(),
+            "scrollable content must not fill its horizontal scrolling axis"
+        );
+
         Scrollable {
             id: None,
             width: Length::Shrink,
             height: Length::Shrink,
-            direction: Direction::default(),
+            direction,
-            content: content.into(),
+            content,
             on_scroll: None,
             style: Default::default(),
         }
@@ -80,12 +102,6 @@ where
         self
     }
 
-    /// Sets the [`Direction`] of the [`Scrollable`] .
-    pub fn direction(mut self, direction: Direction) -> Self {
-        self.direction = direction;
-        self
-    }
-
     /// Sets a function to call when the [`Scrollable`] is scrolled.
     ///
     /// The function takes the [`Viewport`] of the [`Scrollable`]