1//! A list element that can be used to render a large number of differently sized elements
2//! efficiently. Clients of this API need to ensure that elements outside of the scrolled
3//! area do not change their height for this element to function correctly. If your elements
4//! do change height, notify the list element via [`ListState::splice`] or [`ListState::reset`].
5//! In order to minimize re-renders, this element's state is stored intrusively
6//! on your own views, so that your code can coordinate directly with the list element's cached state.
7//!
8//! If all of your elements are the same height, see [`UniformList`] for a simpler API
9
10use crate::{
11 point, px, size, AnyElement, App, AvailableSpace, Bounds, ContentMask, DispatchPhase, Edges,
12 Element, FocusHandle, GlobalElementId, Hitbox, IntoElement, Pixels, Point, ScrollWheelEvent,
13 Size, Style, StyleRefinement, Styled, Window,
14};
15use collections::VecDeque;
16use refineable::Refineable as _;
17use std::{cell::RefCell, ops::Range, rc::Rc};
18use sum_tree::{Bias, SumTree};
19use taffy::style::Overflow;
20
21/// Construct a new list element
22pub fn list(state: ListState) -> List {
23 List {
24 state,
25 style: StyleRefinement::default(),
26 sizing_behavior: ListSizingBehavior::default(),
27 }
28}
29
30/// A list element
31pub struct List {
32 state: ListState,
33 style: StyleRefinement,
34 sizing_behavior: ListSizingBehavior,
35}
36
37impl List {
38 /// Set the sizing behavior for the list.
39 pub fn with_sizing_behavior(mut self, behavior: ListSizingBehavior) -> Self {
40 self.sizing_behavior = behavior;
41 self
42 }
43}
44
45/// The list state that views must hold on behalf of the list element.
46#[derive(Clone)]
47pub struct ListState(Rc<RefCell<StateInner>>);
48
49struct StateInner {
50 last_layout_bounds: Option<Bounds<Pixels>>,
51 last_padding: Option<Edges<Pixels>>,
52 render_item: Box<dyn FnMut(usize, &mut Window, &mut App) -> AnyElement>,
53 items: SumTree<ListItem>,
54 logical_scroll_top: Option<ListOffset>,
55 alignment: ListAlignment,
56 overdraw: Pixels,
57 reset: bool,
58 #[allow(clippy::type_complexity)]
59 scroll_handler: Option<Box<dyn FnMut(&ListScrollEvent, &mut Window, &mut App)>>,
60}
61
62/// Whether the list is scrolling from top to bottom or bottom to top.
63#[derive(Clone, Copy, Debug, Eq, PartialEq)]
64pub enum ListAlignment {
65 /// The list is scrolling from top to bottom, like most lists.
66 Top,
67 /// The list is scrolling from bottom to top, like a chat log.
68 Bottom,
69}
70
71/// A scroll event that has been converted to be in terms of the list's items.
72pub struct ListScrollEvent {
73 /// The range of items currently visible in the list, after applying the scroll event.
74 pub visible_range: Range<usize>,
75
76 /// The number of items that are currently visible in the list, after applying the scroll event.
77 pub count: usize,
78
79 /// Whether the list has been scrolled.
80 pub is_scrolled: bool,
81}
82
83/// The sizing behavior to apply during layout.
84#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
85pub enum ListSizingBehavior {
86 /// The list should calculate its size based on the size of its items.
87 Infer,
88 /// The list should not calculate a fixed size.
89 #[default]
90 Auto,
91}
92
93/// The horizontal sizing behavior to apply during layout.
94#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
95pub enum ListHorizontalSizingBehavior {
96 /// List items' width can never exceed the width of the list.
97 #[default]
98 FitList,
99 /// List items' width may go over the width of the list, if any item is wider.
100 Unconstrained,
101}
102
103struct LayoutItemsResponse {
104 max_item_width: Pixels,
105 scroll_top: ListOffset,
106 item_layouts: VecDeque<ItemLayout>,
107}
108
109struct ItemLayout {
110 index: usize,
111 element: AnyElement,
112 size: Size<Pixels>,
113}
114
115/// Frame state used by the [List] element after layout.
116pub struct ListPrepaintState {
117 hitbox: Hitbox,
118 layout: LayoutItemsResponse,
119}
120
121#[derive(Clone)]
122enum ListItem {
123 Unmeasured {
124 focus_handle: Option<FocusHandle>,
125 },
126 Measured {
127 size: Size<Pixels>,
128 focus_handle: Option<FocusHandle>,
129 },
130}
131
132impl ListItem {
133 fn size(&self) -> Option<Size<Pixels>> {
134 if let ListItem::Measured { size, .. } = self {
135 Some(*size)
136 } else {
137 None
138 }
139 }
140
141 fn focus_handle(&self) -> Option<FocusHandle> {
142 match self {
143 ListItem::Unmeasured { focus_handle } | ListItem::Measured { focus_handle, .. } => {
144 focus_handle.clone()
145 }
146 }
147 }
148
149 fn contains_focused(&self, window: &Window, cx: &App) -> bool {
150 match self {
151 ListItem::Unmeasured { focus_handle } | ListItem::Measured { focus_handle, .. } => {
152 focus_handle
153 .as_ref()
154 .is_some_and(|handle| handle.contains_focused(window, cx))
155 }
156 }
157 }
158}
159
160#[derive(Clone, Debug, Default, PartialEq)]
161struct ListItemSummary {
162 count: usize,
163 rendered_count: usize,
164 unrendered_count: usize,
165 height: Pixels,
166 has_focus_handles: bool,
167}
168
169#[derive(Clone, Debug, Default, PartialEq, Eq, PartialOrd, Ord)]
170struct Count(usize);
171
172#[derive(Clone, Debug, Default)]
173struct Height(Pixels);
174
175impl ListState {
176 /// Construct a new list state, for storage on a view.
177 ///
178 /// The overdraw parameter controls how much extra space is rendered
179 /// above and below the visible area. Elements within this area will
180 /// be measured even though they are not visible. This can help ensure
181 /// that the list doesn't flicker or pop in when scrolling.
182 pub fn new<R>(
183 item_count: usize,
184 alignment: ListAlignment,
185 overdraw: Pixels,
186 render_item: R,
187 ) -> Self
188 where
189 R: 'static + FnMut(usize, &mut Window, &mut App) -> AnyElement,
190 {
191 let this = Self(Rc::new(RefCell::new(StateInner {
192 last_layout_bounds: None,
193 last_padding: None,
194 render_item: Box::new(render_item),
195 items: SumTree::default(),
196 logical_scroll_top: None,
197 alignment,
198 overdraw,
199 scroll_handler: None,
200 reset: false,
201 })));
202 this.splice(0..0, item_count);
203 this
204 }
205
206 /// Reset this instantiation of the list state.
207 ///
208 /// Note that this will cause scroll events to be dropped until the next paint.
209 pub fn reset(&self, element_count: usize) {
210 let old_count = {
211 let state = &mut *self.0.borrow_mut();
212 state.reset = true;
213 state.logical_scroll_top = None;
214 state.items.summary().count
215 };
216
217 self.splice(0..old_count, element_count);
218 }
219
220 /// The number of items in this list.
221 pub fn item_count(&self) -> usize {
222 self.0.borrow().items.summary().count
223 }
224
225 /// Inform the list state that the items in `old_range` have been replaced
226 /// by `count` new items that must be recalculated.
227 pub fn splice(&self, old_range: Range<usize>, count: usize) {
228 self.splice_focusable(old_range, (0..count).map(|_| None))
229 }
230
231 /// Register with the list state that the items in `old_range` have been replaced
232 /// by new items. As opposed to [`splice`], this method allows an iterator of optional focus handles
233 /// to be supplied to properly integrate with items in the list that can be focused. If a focused item
234 /// is scrolled out of view, the list will continue to render it to allow keyboard interaction.
235 pub fn splice_focusable(
236 &self,
237 old_range: Range<usize>,
238 focus_handles: impl IntoIterator<Item = Option<FocusHandle>>,
239 ) {
240 let state = &mut *self.0.borrow_mut();
241
242 let mut old_items = state.items.cursor::<Count>(&());
243 let mut new_items = old_items.slice(&Count(old_range.start), Bias::Right, &());
244 old_items.seek_forward(&Count(old_range.end), Bias::Right, &());
245
246 let mut spliced_count = 0;
247 new_items.extend(
248 focus_handles.into_iter().map(|focus_handle| {
249 spliced_count += 1;
250 ListItem::Unmeasured { focus_handle }
251 }),
252 &(),
253 );
254 new_items.append(old_items.suffix(&()), &());
255 drop(old_items);
256 state.items = new_items;
257
258 if let Some(ListOffset {
259 item_ix,
260 offset_in_item,
261 }) = state.logical_scroll_top.as_mut()
262 {
263 if old_range.contains(item_ix) {
264 *item_ix = old_range.start;
265 *offset_in_item = px(0.);
266 } else if old_range.end <= *item_ix {
267 *item_ix = *item_ix - (old_range.end - old_range.start) + spliced_count;
268 }
269 }
270 }
271
272 /// Set a handler that will be called when the list is scrolled.
273 pub fn set_scroll_handler(
274 &self,
275 handler: impl FnMut(&ListScrollEvent, &mut Window, &mut App) + 'static,
276 ) {
277 self.0.borrow_mut().scroll_handler = Some(Box::new(handler))
278 }
279
280 /// Get the current scroll offset, in terms of the list's items.
281 pub fn logical_scroll_top(&self) -> ListOffset {
282 self.0.borrow().logical_scroll_top()
283 }
284
285 /// Scroll the list to the given offset
286 pub fn scroll_to(&self, mut scroll_top: ListOffset) {
287 let state = &mut *self.0.borrow_mut();
288 let item_count = state.items.summary().count;
289 if scroll_top.item_ix >= item_count {
290 scroll_top.item_ix = item_count;
291 scroll_top.offset_in_item = px(0.);
292 }
293
294 state.logical_scroll_top = Some(scroll_top);
295 }
296
297 /// Scroll the list to the given item, such that the item is fully visible.
298 pub fn scroll_to_reveal_item(&self, ix: usize) {
299 let state = &mut *self.0.borrow_mut();
300
301 let mut scroll_top = state.logical_scroll_top();
302 let height = state
303 .last_layout_bounds
304 .map_or(px(0.), |bounds| bounds.size.height);
305 let padding = state.last_padding.unwrap_or_default();
306
307 if ix <= scroll_top.item_ix {
308 scroll_top.item_ix = ix;
309 scroll_top.offset_in_item = px(0.);
310 } else {
311 let mut cursor = state.items.cursor::<ListItemSummary>(&());
312 cursor.seek(&Count(ix + 1), Bias::Right, &());
313 let bottom = cursor.start().height + padding.top;
314 let goal_top = px(0.).max(bottom - height + padding.bottom);
315
316 cursor.seek(&Height(goal_top), Bias::Left, &());
317 let start_ix = cursor.start().count;
318 let start_item_top = cursor.start().height;
319
320 if start_ix >= scroll_top.item_ix {
321 scroll_top.item_ix = start_ix;
322 scroll_top.offset_in_item = goal_top - start_item_top;
323 }
324 }
325
326 state.logical_scroll_top = Some(scroll_top);
327 }
328
329 /// Get the bounds for the given item in window coordinates, if it's
330 /// been rendered.
331 pub fn bounds_for_item(&self, ix: usize) -> Option<Bounds<Pixels>> {
332 let state = &*self.0.borrow();
333
334 let bounds = state.last_layout_bounds.unwrap_or_default();
335 let scroll_top = state.logical_scroll_top();
336 if ix < scroll_top.item_ix {
337 return None;
338 }
339
340 let mut cursor = state.items.cursor::<(Count, Height)>(&());
341 cursor.seek(&Count(scroll_top.item_ix), Bias::Right, &());
342
343 let scroll_top = cursor.start().1 .0 + scroll_top.offset_in_item;
344
345 cursor.seek_forward(&Count(ix), Bias::Right, &());
346 if let Some(&ListItem::Measured { size, .. }) = cursor.item() {
347 let &(Count(count), Height(top)) = cursor.start();
348 if count == ix {
349 let top = bounds.top() + top - scroll_top;
350 return Some(Bounds::from_corners(
351 point(bounds.left(), top),
352 point(bounds.right(), top + size.height),
353 ));
354 }
355 }
356 None
357 }
358}
359
360impl StateInner {
361 fn visible_range(&self, height: Pixels, scroll_top: &ListOffset) -> Range<usize> {
362 let mut cursor = self.items.cursor::<ListItemSummary>(&());
363 cursor.seek(&Count(scroll_top.item_ix), Bias::Right, &());
364 let start_y = cursor.start().height + scroll_top.offset_in_item;
365 cursor.seek_forward(&Height(start_y + height), Bias::Left, &());
366 scroll_top.item_ix..cursor.start().count + 1
367 }
368
369 fn scroll(
370 &mut self,
371 scroll_top: &ListOffset,
372 height: Pixels,
373 delta: Point<Pixels>,
374 window: &mut Window,
375 cx: &mut App,
376 ) {
377 // Drop scroll events after a reset, since we can't calculate
378 // the new logical scroll top without the item heights
379 if self.reset {
380 return;
381 }
382
383 let padding = self.last_padding.unwrap_or_default();
384 let scroll_max =
385 (self.items.summary().height + padding.top + padding.bottom - height).max(px(0.));
386 let new_scroll_top = (self.scroll_top(scroll_top) - delta.y)
387 .max(px(0.))
388 .min(scroll_max);
389
390 if self.alignment == ListAlignment::Bottom && new_scroll_top == scroll_max {
391 self.logical_scroll_top = None;
392 } else {
393 let mut cursor = self.items.cursor::<ListItemSummary>(&());
394 cursor.seek(&Height(new_scroll_top), Bias::Right, &());
395 let item_ix = cursor.start().count;
396 let offset_in_item = new_scroll_top - cursor.start().height;
397 self.logical_scroll_top = Some(ListOffset {
398 item_ix,
399 offset_in_item,
400 });
401 }
402
403 if self.scroll_handler.is_some() {
404 let visible_range = self.visible_range(height, scroll_top);
405 self.scroll_handler.as_mut().unwrap()(
406 &ListScrollEvent {
407 visible_range,
408 count: self.items.summary().count,
409 is_scrolled: self.logical_scroll_top.is_some(),
410 },
411 window,
412 cx,
413 );
414 }
415
416 window.refresh();
417 }
418
419 fn logical_scroll_top(&self) -> ListOffset {
420 self.logical_scroll_top
421 .unwrap_or_else(|| match self.alignment {
422 ListAlignment::Top => ListOffset {
423 item_ix: 0,
424 offset_in_item: px(0.),
425 },
426 ListAlignment::Bottom => ListOffset {
427 item_ix: self.items.summary().count,
428 offset_in_item: px(0.),
429 },
430 })
431 }
432
433 fn scroll_top(&self, logical_scroll_top: &ListOffset) -> Pixels {
434 let mut cursor = self.items.cursor::<ListItemSummary>(&());
435 cursor.seek(&Count(logical_scroll_top.item_ix), Bias::Right, &());
436 cursor.start().height + logical_scroll_top.offset_in_item
437 }
438
439 fn layout_items(
440 &mut self,
441 available_width: Option<Pixels>,
442 available_height: Pixels,
443 padding: &Edges<Pixels>,
444 window: &mut Window,
445 cx: &mut App,
446 ) -> LayoutItemsResponse {
447 let old_items = self.items.clone();
448 let mut measured_items = VecDeque::new();
449 let mut item_layouts = VecDeque::new();
450 let mut rendered_height = padding.top;
451 let mut max_item_width = px(0.);
452 let mut scroll_top = self.logical_scroll_top();
453 let mut rendered_focused_item = false;
454
455 let available_item_space = size(
456 available_width.map_or(AvailableSpace::MinContent, |width| {
457 AvailableSpace::Definite(width)
458 }),
459 AvailableSpace::MinContent,
460 );
461
462 let mut cursor = old_items.cursor::<Count>(&());
463
464 // Render items after the scroll top, including those in the trailing overdraw
465 cursor.seek(&Count(scroll_top.item_ix), Bias::Right, &());
466 for (ix, item) in cursor.by_ref().enumerate() {
467 let visible_height = rendered_height - scroll_top.offset_in_item;
468 if visible_height >= available_height + self.overdraw {
469 break;
470 }
471
472 // Use the previously cached height and focus handle if available
473 let mut size = item.size();
474
475 // If we're within the visible area or the height wasn't cached, render and measure the item's element
476 if visible_height < available_height || size.is_none() {
477 let item_index = scroll_top.item_ix + ix;
478 let mut element = (self.render_item)(item_index, window, cx);
479 let element_size = element.layout_as_root(available_item_space, window, cx);
480 size = Some(element_size);
481 if visible_height < available_height {
482 item_layouts.push_back(ItemLayout {
483 index: item_index,
484 element,
485 size: element_size,
486 });
487 if item.contains_focused(window, cx) {
488 rendered_focused_item = true;
489 }
490 }
491 }
492
493 let size = size.unwrap();
494 rendered_height += size.height;
495 max_item_width = max_item_width.max(size.width);
496 measured_items.push_back(ListItem::Measured {
497 size,
498 focus_handle: item.focus_handle(),
499 });
500 }
501 rendered_height += padding.bottom;
502
503 // Prepare to start walking upward from the item at the scroll top.
504 cursor.seek(&Count(scroll_top.item_ix), Bias::Right, &());
505
506 // If the rendered items do not fill the visible region, then adjust
507 // the scroll top upward.
508 if rendered_height - scroll_top.offset_in_item < available_height {
509 while rendered_height < available_height {
510 cursor.prev(&());
511 if let Some(item) = cursor.item() {
512 let item_index = cursor.start().0;
513 let mut element = (self.render_item)(item_index, window, cx);
514 let element_size = element.layout_as_root(available_item_space, window, cx);
515 let focus_handle = item.focus_handle();
516 rendered_height += element_size.height;
517 measured_items.push_front(ListItem::Measured {
518 size: element_size,
519 focus_handle,
520 });
521 item_layouts.push_front(ItemLayout {
522 index: item_index,
523 element,
524 size: element_size,
525 });
526 if item.contains_focused(window, cx) {
527 rendered_focused_item = true;
528 }
529 } else {
530 break;
531 }
532 }
533
534 scroll_top = ListOffset {
535 item_ix: cursor.start().0,
536 offset_in_item: rendered_height - available_height,
537 };
538
539 match self.alignment {
540 ListAlignment::Top => {
541 scroll_top.offset_in_item = scroll_top.offset_in_item.max(px(0.));
542 self.logical_scroll_top = Some(scroll_top);
543 }
544 ListAlignment::Bottom => {
545 scroll_top = ListOffset {
546 item_ix: cursor.start().0,
547 offset_in_item: rendered_height - available_height,
548 };
549 self.logical_scroll_top = None;
550 }
551 };
552 }
553
554 // Measure items in the leading overdraw
555 let mut leading_overdraw = scroll_top.offset_in_item;
556 while leading_overdraw < self.overdraw {
557 cursor.prev(&());
558 if let Some(item) = cursor.item() {
559 let size = if let ListItem::Measured { size, .. } = item {
560 *size
561 } else {
562 let mut element = (self.render_item)(cursor.start().0, window, cx);
563 element.layout_as_root(available_item_space, window, cx)
564 };
565
566 leading_overdraw += size.height;
567 measured_items.push_front(ListItem::Measured {
568 size,
569 focus_handle: item.focus_handle(),
570 });
571 } else {
572 break;
573 }
574 }
575
576 let measured_range = cursor.start().0..(cursor.start().0 + measured_items.len());
577 let mut cursor = old_items.cursor::<Count>(&());
578 let mut new_items = cursor.slice(&Count(measured_range.start), Bias::Right, &());
579 new_items.extend(measured_items, &());
580 cursor.seek(&Count(measured_range.end), Bias::Right, &());
581 new_items.append(cursor.suffix(&()), &());
582 self.items = new_items;
583
584 // If none of the visible items are focused, check if an off-screen item is focused
585 // and include it to be rendered after the visible items so keyboard interaction continues
586 // to work for it.
587 if !rendered_focused_item {
588 let mut cursor = self
589 .items
590 .filter::<_, Count>(&(), |summary| summary.has_focus_handles);
591 cursor.next(&());
592 while let Some(item) = cursor.item() {
593 if item.contains_focused(window, cx) {
594 let item_index = cursor.start().0;
595 let mut element = (self.render_item)(cursor.start().0, window, cx);
596 let size = element.layout_as_root(available_item_space, window, cx);
597 item_layouts.push_back(ItemLayout {
598 index: item_index,
599 element,
600 size,
601 });
602 break;
603 }
604 cursor.next(&());
605 }
606 }
607
608 LayoutItemsResponse {
609 max_item_width,
610 scroll_top,
611 item_layouts,
612 }
613 }
614
615 fn prepaint_items(
616 &mut self,
617 bounds: Bounds<Pixels>,
618 padding: Edges<Pixels>,
619 autoscroll: bool,
620 window: &mut Window,
621 cx: &mut App,
622 ) -> Result<LayoutItemsResponse, ListOffset> {
623 window.transact(|window| {
624 let mut layout_response = self.layout_items(
625 Some(bounds.size.width),
626 bounds.size.height,
627 &padding,
628 window,
629 cx,
630 );
631
632 // Avoid honoring autoscroll requests from elements other than our children.
633 window.take_autoscroll();
634
635 // Only paint the visible items, if there is actually any space for them (taking padding into account)
636 if bounds.size.height > padding.top + padding.bottom {
637 let mut item_origin = bounds.origin + Point::new(px(0.), padding.top);
638 item_origin.y -= layout_response.scroll_top.offset_in_item;
639 for item in &mut layout_response.item_layouts {
640 window.with_content_mask(Some(ContentMask { bounds }), |window| {
641 item.element.prepaint_at(item_origin, window, cx);
642 });
643
644 if let Some(autoscroll_bounds) = window.take_autoscroll() {
645 if autoscroll {
646 if autoscroll_bounds.top() < bounds.top() {
647 return Err(ListOffset {
648 item_ix: item.index,
649 offset_in_item: autoscroll_bounds.top() - item_origin.y,
650 });
651 } else if autoscroll_bounds.bottom() > bounds.bottom() {
652 let mut cursor = self.items.cursor::<Count>(&());
653 cursor.seek(&Count(item.index), Bias::Right, &());
654 let mut height = bounds.size.height - padding.top - padding.bottom;
655
656 // Account for the height of the element down until the autoscroll bottom.
657 height -= autoscroll_bounds.bottom() - item_origin.y;
658
659 // Keep decreasing the scroll top until we fill all the available space.
660 while height > Pixels::ZERO {
661 cursor.prev(&());
662 let Some(item) = cursor.item() else { break };
663
664 let size = item.size().unwrap_or_else(|| {
665 let mut item =
666 (self.render_item)(cursor.start().0, window, cx);
667 let item_available_size = size(
668 bounds.size.width.into(),
669 AvailableSpace::MinContent,
670 );
671 item.layout_as_root(item_available_size, window, cx)
672 });
673 height -= size.height;
674 }
675
676 return Err(ListOffset {
677 item_ix: cursor.start().0,
678 offset_in_item: if height < Pixels::ZERO {
679 -height
680 } else {
681 Pixels::ZERO
682 },
683 });
684 }
685 }
686 }
687
688 item_origin.y += item.size.height;
689 }
690 } else {
691 layout_response.item_layouts.clear();
692 }
693
694 Ok(layout_response)
695 })
696 }
697}
698
699impl std::fmt::Debug for ListItem {
700 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
701 match self {
702 Self::Unmeasured { .. } => write!(f, "Unrendered"),
703 Self::Measured { size, .. } => f.debug_struct("Rendered").field("size", size).finish(),
704 }
705 }
706}
707
708/// An offset into the list's items, in terms of the item index and the number
709/// of pixels off the top left of the item.
710#[derive(Debug, Clone, Copy, Default)]
711pub struct ListOffset {
712 /// The index of an item in the list
713 pub item_ix: usize,
714 /// The number of pixels to offset from the item index.
715 pub offset_in_item: Pixels,
716}
717
718impl Element for List {
719 type RequestLayoutState = ();
720 type PrepaintState = ListPrepaintState;
721
722 fn id(&self) -> Option<crate::ElementId> {
723 None
724 }
725
726 fn request_layout(
727 &mut self,
728 _id: Option<&GlobalElementId>,
729 window: &mut Window,
730 cx: &mut App,
731 ) -> (crate::LayoutId, Self::RequestLayoutState) {
732 let layout_id = match self.sizing_behavior {
733 ListSizingBehavior::Infer => {
734 let mut style = Style::default();
735 style.overflow.y = Overflow::Scroll;
736 style.refine(&self.style);
737 window.with_text_style(style.text_style().cloned(), |window| {
738 let state = &mut *self.state.0.borrow_mut();
739
740 let available_height = if let Some(last_bounds) = state.last_layout_bounds {
741 last_bounds.size.height
742 } else {
743 // If we don't have the last layout bounds (first render),
744 // we might just use the overdraw value as the available height to layout enough items.
745 state.overdraw
746 };
747 let padding = style.padding.to_pixels(
748 state.last_layout_bounds.unwrap_or_default().size.into(),
749 window.rem_size(),
750 );
751
752 let layout_response =
753 state.layout_items(None, available_height, &padding, window, cx);
754 let max_element_width = layout_response.max_item_width;
755
756 let summary = state.items.summary();
757 let total_height = summary.height;
758
759 window.request_measured_layout(
760 style,
761 move |known_dimensions, available_space, _window, _cx| {
762 let width =
763 known_dimensions
764 .width
765 .unwrap_or(match available_space.width {
766 AvailableSpace::Definite(x) => x,
767 AvailableSpace::MinContent | AvailableSpace::MaxContent => {
768 max_element_width
769 }
770 });
771 let height = match available_space.height {
772 AvailableSpace::Definite(height) => total_height.min(height),
773 AvailableSpace::MinContent | AvailableSpace::MaxContent => {
774 total_height
775 }
776 };
777 size(width, height)
778 },
779 )
780 })
781 }
782 ListSizingBehavior::Auto => {
783 let mut style = Style::default();
784 style.refine(&self.style);
785 window.with_text_style(style.text_style().cloned(), |window| {
786 window.request_layout(style, None, cx)
787 })
788 }
789 };
790 (layout_id, ())
791 }
792
793 fn prepaint(
794 &mut self,
795 _id: Option<&GlobalElementId>,
796 bounds: Bounds<Pixels>,
797 _: &mut Self::RequestLayoutState,
798 window: &mut Window,
799 cx: &mut App,
800 ) -> ListPrepaintState {
801 let state = &mut *self.state.0.borrow_mut();
802 state.reset = false;
803
804 let mut style = Style::default();
805 style.refine(&self.style);
806
807 let hitbox = window.insert_hitbox(bounds, false);
808
809 // If the width of the list has changed, invalidate all cached item heights
810 if state.last_layout_bounds.map_or(true, |last_bounds| {
811 last_bounds.size.width != bounds.size.width
812 }) {
813 let new_items = SumTree::from_iter(
814 state.items.iter().map(|item| ListItem::Unmeasured {
815 focus_handle: item.focus_handle(),
816 }),
817 &(),
818 );
819
820 state.items = new_items;
821 }
822
823 let padding = style
824 .padding
825 .to_pixels(bounds.size.into(), window.rem_size());
826 let layout = match state.prepaint_items(bounds, padding, true, window, cx) {
827 Ok(layout) => layout,
828 Err(autoscroll_request) => {
829 state.logical_scroll_top = Some(autoscroll_request);
830 state
831 .prepaint_items(bounds, padding, false, window, cx)
832 .unwrap()
833 }
834 };
835
836 state.last_layout_bounds = Some(bounds);
837 state.last_padding = Some(padding);
838 ListPrepaintState { hitbox, layout }
839 }
840
841 fn paint(
842 &mut self,
843 _id: Option<&GlobalElementId>,
844 bounds: Bounds<crate::Pixels>,
845 _: &mut Self::RequestLayoutState,
846 prepaint: &mut Self::PrepaintState,
847 window: &mut Window,
848 cx: &mut App,
849 ) {
850 window.with_content_mask(Some(ContentMask { bounds }), |window| {
851 for item in &mut prepaint.layout.item_layouts {
852 item.element.paint(window, cx);
853 }
854 });
855
856 let list_state = self.state.clone();
857 let height = bounds.size.height;
858 let scroll_top = prepaint.layout.scroll_top;
859 let hitbox_id = prepaint.hitbox.id;
860 window.on_mouse_event(move |event: &ScrollWheelEvent, phase, window, cx| {
861 if phase == DispatchPhase::Bubble && hitbox_id.is_hovered(window) {
862 list_state.0.borrow_mut().scroll(
863 &scroll_top,
864 height,
865 event.delta.pixel_delta(px(20.)),
866 window,
867 cx,
868 )
869 }
870 });
871 }
872}
873
874impl IntoElement for List {
875 type Element = Self;
876
877 fn into_element(self) -> Self::Element {
878 self
879 }
880}
881
882impl Styled for List {
883 fn style(&mut self) -> &mut StyleRefinement {
884 &mut self.style
885 }
886}
887
888impl sum_tree::Item for ListItem {
889 type Summary = ListItemSummary;
890
891 fn summary(&self, _: &()) -> Self::Summary {
892 match self {
893 ListItem::Unmeasured { focus_handle } => ListItemSummary {
894 count: 1,
895 rendered_count: 0,
896 unrendered_count: 1,
897 height: px(0.),
898 has_focus_handles: focus_handle.is_some(),
899 },
900 ListItem::Measured {
901 size, focus_handle, ..
902 } => ListItemSummary {
903 count: 1,
904 rendered_count: 1,
905 unrendered_count: 0,
906 height: size.height,
907 has_focus_handles: focus_handle.is_some(),
908 },
909 }
910 }
911}
912
913impl sum_tree::Summary for ListItemSummary {
914 type Context = ();
915
916 fn zero(_cx: &()) -> Self {
917 Default::default()
918 }
919
920 fn add_summary(&mut self, summary: &Self, _: &()) {
921 self.count += summary.count;
922 self.rendered_count += summary.rendered_count;
923 self.unrendered_count += summary.unrendered_count;
924 self.height += summary.height;
925 self.has_focus_handles |= summary.has_focus_handles;
926 }
927}
928
929impl<'a> sum_tree::Dimension<'a, ListItemSummary> for Count {
930 fn zero(_cx: &()) -> Self {
931 Default::default()
932 }
933
934 fn add_summary(&mut self, summary: &'a ListItemSummary, _: &()) {
935 self.0 += summary.count;
936 }
937}
938
939impl<'a> sum_tree::Dimension<'a, ListItemSummary> for Height {
940 fn zero(_cx: &()) -> Self {
941 Default::default()
942 }
943
944 fn add_summary(&mut self, summary: &'a ListItemSummary, _: &()) {
945 self.0 += summary.height;
946 }
947}
948
949impl sum_tree::SeekTarget<'_, ListItemSummary, ListItemSummary> for Count {
950 fn cmp(&self, other: &ListItemSummary, _: &()) -> std::cmp::Ordering {
951 self.0.partial_cmp(&other.count).unwrap()
952 }
953}
954
955impl sum_tree::SeekTarget<'_, ListItemSummary, ListItemSummary> for Height {
956 fn cmp(&self, other: &ListItemSummary, _: &()) -> std::cmp::Ordering {
957 self.0.partial_cmp(&other.height).unwrap()
958 }
959}
960
961#[cfg(test)]
962mod test {
963
964 use gpui::{ScrollDelta, ScrollWheelEvent};
965
966 use crate::{self as gpui, TestAppContext};
967
968 #[gpui::test]
969 fn test_reset_after_paint_before_scroll(cx: &mut TestAppContext) {
970 use crate::{div, list, point, px, size, Element, ListState, Styled};
971
972 let cx = cx.add_empty_window();
973
974 let state = ListState::new(5, crate::ListAlignment::Top, px(10.), |_, _, _| {
975 div().h(px(10.)).w_full().into_any()
976 });
977
978 // Ensure that the list is scrolled to the top
979 state.scroll_to(gpui::ListOffset {
980 item_ix: 0,
981 offset_in_item: px(0.0),
982 });
983
984 // Paint
985 cx.draw(point(px(0.), px(0.)), size(px(100.), px(20.)), |_, _| {
986 list(state.clone()).w_full().h_full()
987 });
988
989 // Reset
990 state.reset(5);
991
992 // And then receive a scroll event _before_ the next paint
993 cx.simulate_event(ScrollWheelEvent {
994 position: point(px(1.), px(1.)),
995 delta: ScrollDelta::Pixels(point(px(0.), px(-500.))),
996 ..Default::default()
997 });
998
999 // Scroll position should stay at the top of the list
1000 assert_eq!(state.logical_scroll_top().item_ix, 0);
1001 assert_eq!(state.logical_scroll_top().offset_in_item, px(0.));
1002 }
1003}