[JEWEL-1244] Fix ListComboBox External SelectedIndex Changes Not Syncing To Internal State

[DanielSouzaBertoldi]

Context

Currently, our Combo Box implementation only updates its selected index internally. This means that, if users want to programmatically change it, the change won't be respected by our Combo Box. If the user clicks on a ComboBox, it'll show the value of whatever the user chose previously as the current selected item, not the item that was set by the code.

Changes

• Added selectedIndex to our LaunchedEffect in ComboBoxImpl, so that we can update the list state with the current selected index
• Added unit tests

If you'd like to test this yourself, apply the git patch below:

Details

Index: platform/jewel/samples/showcase/src/main/kotlin/org/jetbrains/jewel/samples/showcase/components/ComboBoxes.kt
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/platform/jewel/samples/showcase/src/main/kotlin/org/jetbrains/jewel/samples/showcase/components/ComboBoxes.kt b/platform/jewel/samples/showcase/src/main/kotlin/org/jetbrains/jewel/samples/showcase/components/ComboBoxes.kt
--- a/platform/jewel/samples/showcase/src/main/kotlin/org/jetbrains/jewel/samples/showcase/components/ComboBoxes.kt	(revision db891e692f6611bc85709ecbe66a8b0fe87d226b)
+++ b/platform/jewel/samples/showcase/src/main/kotlin/org/jetbrains/jewel/samples/showcase/components/ComboBoxes.kt	(date 1770752708307)
@@ -2,6 +2,7 @@
 // Apache 2.0 license.
 package org.jetbrains.jewel.samples.showcase.components
 
+import androidx.compose.foundation.clickable
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.FlowRow
@@ -101,10 +102,8 @@
 private fun ListComboBoxes() {
     FlowRow(horizontalArrangement = Arrangement.spacedBy(8.dp), verticalArrangement = Arrangement.spacedBy(8.dp)) {
         Column(Modifier.weight(1f).widthIn(min = 125.dp), verticalArrangement = Arrangement.spacedBy(8.dp)) {
-            Text("String-based API")
-            var selectedIndex by remember { mutableIntStateOf(2) }
-            val selectedItemText = if (selectedIndex >= 0) stringItems[selectedIndex] else "[none]"
-            InfoText(text = "Selected item: $selectedItemText")
+            var selectedIndex by remember { mutableIntStateOf(0) }
+            Text("Reset", modifier = Modifier.clickable(onClick = { selectedIndex = 0 }))
 
             ListComboBox(
                 items = stringItems,
@@ -203,8 +202,8 @@
 private fun EditableListComboBoxes() {
     FlowRow(horizontalArrangement = Arrangement.spacedBy(8.dp), verticalArrangement = Arrangement.spacedBy(8.dp)) {
         Column(Modifier.weight(1f).widthIn(min = 125.dp), verticalArrangement = Arrangement.spacedBy(8.dp)) {
-            Text("String-based API, enabled")
-            var selectedIndex by remember { mutableIntStateOf(2) }
+            var selectedIndex by remember { mutableIntStateOf(0) }
+            Text("Reset", modifier = Modifier.clickable(onClick = { selectedIndex = 0 }))
             val selectedItemText = if (selectedIndex >= 0) stringItems[selectedIndex] else "[none]"
             InfoText(text = "Selected item: $selectedItemText")
 

Evidences

	Before	After
ListComboBox	Screen.Recording.2026-02-10.at.16.47.24.mov	Screen.Recording.2026-02-10.at.16.43.26.mov
EditableComboBox	Screen.Recording.2026-02-10.at.16.47.54.mov	Screen.Recording.2026-02-10.at.16.43.54.mov

[DanielSouzaBertoldi]

We really don't want to mess with the popup while its visible and the user is actively using it. This prevents any changes made programmatically from happening during this state.