feat(settings): add on_page_change callback to Settings widget

crates/story/src/stories/settings_story.rs

@@ -61,6 +61,7 @@ pub struct SettingsStory {
     focus_handle: FocusHandle,
     group_variant: GroupBoxVariant,
     size: Size,
+    last_page_index: usize,
 }
 
 struct OpenURLSettingField {
@@ -121,6 +122,7 @@ impl SettingsStory {
             focus_handle: cx.focus_handle(),
             group_variant: GroupBoxVariant::Outline,
             size: Size::default(),
+            last_page_index: 0,
         }
     }
 
@@ -455,9 +457,20 @@ impl Focusable for SettingsStory {
 
 impl Render for SettingsStory {
     fn render(&mut self, window: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
+        let entity = cx.entity();
         Settings::new("app-settings")
             .with_size(self.size)
             .with_group_variant(self.group_variant)
+            .default_selected_index(gpui_component::setting::SelectIndex {
+                page_ix: self.last_page_index,
+                group_ix: None,
+            })
+            .on_page_change(move |ix, cx| {
+                entity.update(cx, |this, cx| {
+                    this.last_page_index = ix;
+                    cx.notify();
+                });
+            })
             .pages(self.setting_pages(window, cx))
     }
 }

crates/ui/src/setting/settings.rs

@@ -11,6 +11,7 @@ use gpui::{
     RenderOnce, StyleRefinement, Styled, Window, div, prelude::FluentBuilder as _, px, relative,
 };
 use rust_i18n::t;
+use std::rc::Rc;
 
 /// The settings structure containing multiple pages for app settings.
 ///
@@ -34,6 +35,7 @@ pub struct Settings {
     sidebar_style: StyleRefinement,
     default_selected_index: SelectIndex,
     header_style: StyleRefinement,
+    on_page_change: Option<Rc<dyn Fn(usize, &mut App) + 'static>>,
 }
 
 impl Settings {
@@ -48,6 +50,7 @@ impl Settings {
             sidebar_style: StyleRefinement::default(),
             default_selected_index: SelectIndex::default(),
             header_style: StyleRefinement::default(),
+            on_page_change: None,
         }
     }
 
@@ -95,6 +98,15 @@ impl Settings {
         self
     }
 
+    /// Set a callback invoked when the user selects a top-level page in the sidebar.
+    ///
+    /// The first argument is the zero-based page index. This is useful for persisting
+    /// the last-visited page so it can be restored via [`Self::default_selected_index`].
+    pub fn on_page_change(mut self, f: impl Fn(usize, &mut App) + 'static) -> Self {
+        self.on_page_change = Some(Rc::new(f));
+        self
+    }
+
     fn filtered_pages(&self, query: &str, cx: &App) -> Vec<SettingPage> {
         self.pages
             .iter()
@@ -153,6 +165,7 @@ impl Settings {
         &self,
         state: &Entity<SettingsState>,
         pages: &Vec<SettingPage>,
+        on_page_change: Option<Rc<dyn Fn(usize, &mut App) + 'static>>,
         _: &mut Window,
         cx: &mut App,
     ) -> impl IntoElement {
@@ -182,14 +195,18 @@ impl Settings {
                         .active(is_page_active)
                         .on_click({
                             let state = state.clone();
+                            let on_page_change = on_page_change.clone();
                             move |_, _, cx| {
                                 state.update(cx, |state, cx| {
                                     state.selected_index = SelectIndex {
                                         page_ix,
                                         ..Default::default()
                                     };
                                     cx.notify();
-                                })
+                                });
+                                if let Some(f) = &on_page_change {
+                                    f(page_ix, cx);
+                                }
                             }
                         })
                         .when(page.groups.len() > 1, |this| {
@@ -288,7 +305,7 @@ impl RenderOnce for Settings {
             .child(
                 resizable_panel()
                     .size(self.sidebar_width)
-                    .child(self.render_sidebar(&state, &filtered_pages, window, cx)),
+                    .child(self.render_sidebar(&state, &filtered_pages, self.on_page_change.clone(), window, cx)),
             )
             .child(resizable_panel().child(self.render_active_page(
                 &state,