[lvgl] Fix on_value/on_update triggers for LVGL select entities (#18778)

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

esphome/components/lvgl/lvgl_esphome.cpp

@@ -551,21 +551,21 @@ std::string LvSelectable::get_selected_text() {
   return this->options_[selected];
 }
 
-static std::string join_string(std::vector<std::string> options) {
+static std::string join_string(const FixedVector<const char *> &options) {
   return std::accumulate(
       options.begin(), options.end(), std::string(),
-      [](const std::string &a, const std::string &b) -> std::string { return a + (!a.empty() ? "\n" : "") + b; });
+      [](const std::string &a, const char *b) -> std::string { return a + (!a.empty() ? "\n" : "") + b; });
 }
 
 void LvSelectable::set_selected_text(const std::string &text, lv_anim_enable_t anim) {
-  auto index = std::find(this->options_.begin(), this->options_.end(), text);
+  auto *index = std::find(this->options_.begin(), this->options_.end(), text);
   if (index != this->options_.end()) {
     this->set_selected_index(index - this->options_.begin(), anim);
     lv_obj_send_event(this->obj, lv_update_event, nullptr);
   }
 }
 
-void LvSelectable::set_options(std::vector<std::string> options) {
+void LvSelectable::set_options(FixedVector<const char *> options) {
   auto index = this->get_selected_index();
   if (index >= options.size())
     index = options.size() - 1;

esphome/components/lvgl/lvgl_esphome.h

@@ -499,12 +499,12 @@ class LvSelectable : public LvCompound {
   virtual void set_selected_index(size_t index, lv_anim_enable_t anim) = 0;
   void set_selected_text(const std::string &text, lv_anim_enable_t anim);
   std::string get_selected_text();
-  const std::vector<std::string> &get_options() { return this->options_; }
-  void set_options(std::vector<std::string> options);
+  const FixedVector<const char *> &get_options() { return this->options_; }
+  void set_options(FixedVector<const char *> options);
 
  protected:
   virtual void set_option_string(const char *options) = 0;
-  std::vector<std::string> options_{};
+  FixedVector<const char *> options_{};
 };
 
 #ifdef USE_LVGL_DROPDOWN

esphome/components/lvgl/select/lvgl_select.h

@@ -50,19 +50,10 @@ class LVGLSelect final : public select::Select, public Component {
  protected:
   void control(size_t index) override {
     this->widget_->set_selected_index(index, this->anim_);
-    this->publish();
-  }
-  void set_options_() {
-    // Widget uses std::vector<std::string>, SelectTraits uses FixedVector<const char*>
-    // Convert by extracting c_str() pointers
-    const auto &opts = this->widget_->get_options();
-    FixedVector<const char *> opt_ptrs;
-    opt_ptrs.init(opts.size());
-    for (const auto &opt : opts) {
-      opt_ptrs.push_back(opt.c_str());
-    }
-    this->traits.set_options(opt_ptrs);
+    // The update event fires the widget's on_value/on_update triggers
+    lv_obj_send_event(this->widget_->obj, lv_update_event, nullptr);
   }
+  void set_options_() { this->traits.set_options(this->widget_->get_options()); }
 
   LvSelectable *widget_;
   lv_anim_enable_t anim_;

esphome/components/lvgl/types.py

@@ -3,6 +3,8 @@ from esphome.const import CONF_TEXT, CONF_VALUE
 from esphome.cpp_generator import MockObj
 from esphome.cpp_types import Component, esphome_ns
 
+from .defines import CONF_SELECTED_INDEX
+
 
 class LvType(cg.MockObjClass):
     def __init__(self, *args, **kwargs):
@@ -112,3 +114,4 @@ class LvSelect(LvType):
             parents=parens,
             **kwargs,
         )
+        self.value_property = CONF_SELECTED_INDEX

tests/component_tests/lvgl/config/dropdown_update_fires_event_test.yaml

@@ -0,0 +1,36 @@
+esphome:
+  name: test-dropdown-update-event
+  on_boot:
+    - lvgl.dropdown.update:
+        id: test_dropdown
+        selected_index: 2
+
+esp32:
+  board: lolin_c3_mini
+
+spi:
+  mosi_pin:
+    number: GPIO2
+    ignore_strapping_warning: true
+  clk_pin: GPIO1
+
+display:
+  - platform: mipi_spi
+    data_rate: 20MHz
+    model: st7735
+    cs_pin:
+      number: GPIO8
+      ignore_strapping_warning: true
+    dc_pin: GPIO3
+
+lvgl:
+  widgets:
+    - dropdown:
+        id: test_dropdown
+        options:
+          - First
+          - Second
+          - Third
+        on_update:
+          - lambda: |-
+              ESP_LOGD("test", "dropdown updated");

tests/component_tests/lvgl/test_dropdown_update_fires_event.py

@@ -0,0 +1,41 @@
+"""Regression test: lvgl.dropdown.update with selected_index must fire on_value/on_update.
+
+LvSelect (backing both dropdown and roller) did not set `value_property`, so the generic
+update-action machinery in automation.py never sent the synthetic update event for a
+`selected_index:` change made via `lvgl.dropdown.update`/`lvgl.roller.update`, unlike `value:`
+on number widgets or `text:` on text widgets. Fixed by setting `LvSelect.value_property` to
+`CONF_SELECTED_INDEX`.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+
+from esphome.__main__ import generate_cpp_contents
+from esphome.config import read_config
+from esphome.core import CORE
+
+
+@pytest.fixture(scope="module")
+def main_cpp(request: pytest.FixtureRequest) -> str:
+    config_path = (
+        Path(request.fspath).parent / "config" / "dropdown_update_fires_event_test.yaml"
+    )
+    original_path = CORE.config_path
+    try:
+        CORE.config_path = config_path
+        CORE.config = read_config({})
+        generate_cpp_contents(CORE.config)
+        return CORE.cpp_main_section
+    finally:
+        CORE.config_path = original_path
+        CORE.reset()
+
+
+def test_dropdown_update_sends_update_event(main_cpp: str) -> None:
+    assert (
+        "lv_obj_send_event(test_dropdown->obj, lvgl::lv_update_event, nullptr)"
+        in main_cpp
+    )