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fix(masonry): flex layout not running after removing child #981

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fix(masonry): flex layout not running after removing child #981

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3 changes: 3 additions & 0 deletions masonry/screenshots/flex_remove_child_after_expanded_child.png
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31 changes: 29 additions & 2 deletions masonry/src/widgets/flex.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@ pub struct Flex {
fill_major_axis: bool,
children: Vec<Child>,
old_bc: BoxConstraints,
child_removed: bool, // TODO: why can't we use WidgetState.children_changed instead?
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The reason we can't use children_changed here is two reasons:

  1. It will always be handled "before" we get to layout. Indeed, that's the reason that it doesn't have a getter - at this point in the timeline, it doesn't have a meaningful value.
  2. It doesn't handle spacers being removed

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That is, we should remove this comment.

gap: Option<f64>,
}

Expand Down Expand Up @@ -128,6 +129,7 @@ impl Flex {
main_alignment: MainAxisAlignment::Start,
fill_major_axis: false,
old_bc: BoxConstraints::tight(Size::ZERO),
child_removed: false,
gap: None,
}
}
Expand Down Expand Up @@ -579,6 +581,7 @@ impl Flex {
if let Child::Fixed { widget, .. } | Child::Flex { widget, .. } = child {
this.ctx.remove_child(widget);
}
this.widget.child_removed = true;
this.ctx.request_layout();
}

Expand Down Expand Up @@ -1009,7 +1012,8 @@ impl Widget for Flex {
// indicates that the box constrains for the following children have changed. Therefore they
// have to calculate layout again.
let bc_changed = self.old_bc != *bc;
let mut any_changed = bc_changed;
let mut any_changed = bc_changed || self.child_removed;
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@DJMcNab DJMcNab May 20, 2025 •
edited
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Effectively, any_changed is being used a proxy for if the amount of "available flex space" has changed since last run, right?

This all feels very fragile.

I wonder if just expressing that "directly" would make this better? This doesn't need to happen in this PR

self.child_removed = false;
self.old_bc = *bc;

let gap = self.gap.unwrap_or(axis_default_spacer(self.direction));
Expand Down Expand Up @@ -1289,10 +1293,12 @@ impl Widget for Flex {
// --- MARK: TESTS ---
#[cfg(test)]
mod tests {
use vello::peniko::color::palette;

use super::*;
use crate::assert_render_snapshot;
use crate::testing::TestHarness;
use crate::widgets::Label;
use crate::widgets::{Label, SizedBox};

#[test]
#[allow(clippy::cognitive_complexity)]
Expand Down Expand Up @@ -1661,6 +1667,27 @@ mod tests {
assert!(image_1 == image_2);
}

#[test]
fn remove_child_after_expanded_child() {
let widget = Flex::column()
.with_flex_child(
SizedBox::new(Label::new("child 1"))
.expand()
.background(palette::css::PURPLE),
1.,
)
.with_flex_child(Label::new("child 2"), 1.0);

let window_size = Size::new(200.0, 150.0);
let mut harness = TestHarness::create_with_size(widget, window_size);

harness.edit_root_widget(|mut flex| {
let mut flex = flex.downcast::<Flex>();
Flex::remove_child(&mut flex, 1);
});
assert_render_snapshot!(harness, "flex_remove_child_after_expanded_child");
}
Comment on lines +1670 to +1689
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Would you mind adding a similar test where the removed item is a spacer? I believe that this PR should also fix that, but I'd like to be sure.


#[test]
fn get_flex_child() {
let widget = Flex::column()
Expand Down
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