[camera_android_camerax] Fixes crash on hot restart caused by stale observers

packages/camera/camera_android_camerax/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.6.25+1
+
+* Fixes crash on hot restart caused by stale observers.
+
 ## 0.6.25
 
 * Adds support for `MediaSettings.fps` for camera preview, image streaming, and video recording.

packages/camera/camera_android_camerax/android/src/main/java/io/flutter/plugins/camerax/ObserverProxyApi.java

@@ -29,6 +29,19 @@ public void onChanged(T t) {
               new ProxyApiRegistrar.FlutterMethodRunnable() {
                 @Override
                 public void run() {
+                  // Check if this observer instance is still in the instance manager.
+                  // During hot restart, old observers may remain attached to LiveData but
+                  // are no longer tracked in the instance manager.
+                  if (!api.getPigeonRegistrar()
+                      .getInstanceManager()
+                      .containsInstance(ObserverImpl.this)) {
+                    android.util.Log.w(
+                        "ObserverProxyApi",
+                        "Ignoring onChanged callback for Observer not in InstanceManager (likely from previous hot restart): "
+                            + ObserverImpl.this);
+                    return;
+                  }
+
                   api.onChanged(
                       ObserverImpl.this,
                       t,

packages/camera/camera_android_camerax/android/src/test/java/io/flutter/plugins/camerax/ObserverTest.java

@@ -7,22 +7,43 @@
 import static org.mockito.Mockito.any;
 import static org.mockito.Mockito.eq;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
+import org.junit.Before;
 import org.junit.Test;
 
 public class ObserverTest {
+  private ObserverProxyApi mockApi;
+  private TestProxyApiRegistrar registrar;
+  private ObserverProxyApi.ObserverImpl<String> instance;
+
+  @Before
+  public void setUp() {
+    mockApi = mock(ObserverProxyApi.class);
+    registrar = new TestProxyApiRegistrar();
+    when(mockApi.getPigeonRegistrar()).thenReturn(registrar);
+    instance = new ObserverProxyApi.ObserverImpl<>(mockApi);
+  }
+
   @Test
   public void onChanged_makesExpectedCallToDartCallback() {
-    final ObserverProxyApi mockApi = mock(ObserverProxyApi.class);
-    when(mockApi.getPigeonRegistrar()).thenReturn(new TestProxyApiRegistrar());
+    // Add the observer to the instance manager to simulate normal operation
+    registrar.getInstanceManager().addDartCreatedInstance(instance, 0);
 
-    final ObserverProxyApi.ObserverImpl<String> instance =
-        new ObserverProxyApi.ObserverImpl<>(mockApi);
     final String value = "result";
     instance.onChanged(value);
 
     verify(mockApi).onChanged(eq(instance), eq(value), any());
   }
+
+  @Test
+  public void onChanged_doesNotCallDartCallbackWhenObserverNotInInstanceManager() {
+    final String value = "result";
+    instance.onChanged(value);
+
+    // Verify that the Dart callback is NOT invoked for stale observers
+    verify(mockApi, never()).onChanged(any(), any(), any());
+  }
 }

packages/camera/camera_android_camerax/pubspec.yaml

@@ -2,7 +2,7 @@ name: camera_android_camerax
 description: Android implementation of the camera plugin using the CameraX library.
 repository: https://github.com/flutter/packages/tree/main/packages/camera/camera_android_camerax
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+camera%22
-version: 0.6.25
+version: 0.6.25+1
 
 environment:
   sdk: ^3.9.0