dropdown: Add display_title to DropdownItem to support custom title to dropdown input. (#816)

Co-authored-by: Jason Lee <huacnlee@gmail.com>

crates/story/src/dropdown_story.rs

@@ -42,6 +42,10 @@ impl DropdownItem for Country {
         self.name.clone()
     }
 
+    fn display_title(&self) -> Option<gpui::AnyElement> {
+        Some(format!("{} ({})", self.name, self.code).into_any_element())
+    }
+
     fn value(&self) -> &Self::Value {
         &self.code
     }

crates/ui/src/dropdown.rs

@@ -43,6 +43,12 @@ pub fn init(cx: &mut App) {
 pub trait DropdownItem {
     type Value: Clone;
     fn title(&self) -> SharedString;
+    /// Customize the display title used to selected item in Dropdown Input.
+    ///
+    /// If return None, the title will be used.
+    fn display_title(&self) -> Option<AnyElement> {
+        None
+    }
     fn value(&self) -> &Self::Value;
 }
 
@@ -550,33 +556,49 @@ where
         cx.emit(DropdownEvent::Confirm(None));
     }
 
+    /// Returns the title element for the dropdown input.
     fn display_title(&self, _: &Window, cx: &App) -> impl IntoElement {
-        let title = if let Some(selected_index) = &self.selected_index(cx) {
+        let default_title = div()
-            let mut title = self
+            .text_color(cx.theme().accent_foreground)
-                .list
+            .child(
-                .read(cx)
-                .delegate()
-                .delegate
-                .get(*selected_index)
-                .map(|item| item.title().to_string())
-                .unwrap_or_default();
-
-            if let Some(prefix) = self.title_prefix.as_ref() {
-                title = format!("{}{}", prefix, title);
-            }
-
-            div().child(title.clone())
-        } else {
-            div().text_color(cx.theme().accent_foreground).child(
                 self.placeholder
                     .clone()
                     .unwrap_or_else(|| t!("Dropdown.placeholder").into()),
             )
+            .when(self.disabled, |this| {
+                this.text_color(cx.theme().muted_foreground)
+            });
+
+        let Some(selected_index) = &self.selected_index(cx) else {
+            return default_title;
         };
 
-        title.when(self.disabled, |this| {
+        let Some(title) = self
-            this.text_color(cx.theme().muted_foreground)
+            .list
-        })
+            .read(cx)
+            .delegate()
+            .delegate
+            .get(*selected_index)
+            .map(|item| {
+                if let Some(el) = item.display_title() {
+                    el
+                } else {
+                    if let Some(prefix) = self.title_prefix.as_ref() {
+                        format!("{}{}", prefix, item.title()).into_any_element()
+                    } else {
+                        item.title().into_any_element()
+                    }
+                }
+            })
+        else {
+            return default_title;
+        };
+
+        div()
+            .when(self.disabled, |this| {
+                this.text_color(cx.theme().muted_foreground)
+            })
+            .child(title)
     }
 }