fix(android): Release PreviewView when the React view is dropped

apps/simple-camera/__tests__/visioncamera.nativepreviewview.harness.tsx

@@ -722,6 +722,104 @@ describe('VisionCamera - NativePreviewView', () => {
     }
   })
 
+  it('re-attaches a preview output to a new NativePreviewView that replaces the old one while running', async () => {
+    const session = await VisionCamera.createCameraSession(false)
+    const previewOutput = VisionCamera.createPreviewOutput()
+    await session.configure([
+      {
+        input: backDevice,
+        outputs: [{ output: previewOutput, mirrorMode: 'auto' }],
+        constraints: [],
+      },
+    ])
+
+    const firstRef = deferred<PreviewView>()
+    const secondRef = deferred<PreviewView>()
+    const firstLayout = deferred<Layout>()
+    const secondLayout = deferred<Layout>()
+    const firstPreviewStarted = deferred()
+    const secondPreviewStarted = deferred()
+    const errorSub = session.addOnErrorListener((error) => {
+      firstRef.reject(error)
+      secondRef.reject(error)
+      firstLayout.reject(error)
+      secondLayout.reject(error)
+      firstPreviewStarted.reject(error)
+      secondPreviewStarted.reject(error)
+    })
+
+    try {
+      const { rerender } = await render(
+        <NativePreviewView
+          key="first"
+          style={StyleSheet.absoluteFill}
+          previewOutput={previewOutput}
+          hybridRef={callback((preview: PreviewView) => {
+            firstRef.resolve(preview)
+          })}
+          onLayout={(event) => {
+            firstLayout.resolve(toLayout(event))
+          }}
+          onPreviewStarted={callback(firstPreviewStarted.resolve)}
+        />,
+      )
+
+      const firstPreview = await withTimeout(
+        firstRef.promise,
+        10_000,
+        'first NativePreviewView hybridRef',
+      )
+      const firstPreviewLayout = await withTimeout(
+        firstLayout.promise,
+        10_000,
+        'first NativePreviewView onLayout',
+      )
+
+      await session.start()
+      await withTimeout(
+        firstPreviewStarted.promise,
+        15_000,
+        'first NativePreviewView onPreviewStarted',
+      )
+      expectPreviewGeometry(firstPreview, firstPreviewLayout)
+
+      await rerender(
+        <NativePreviewView
+          key="second"
+          style={StyleSheet.absoluteFill}
+          previewOutput={previewOutput}
+          hybridRef={callback((preview: PreviewView) => {
+            secondRef.resolve(preview)
+          })}
+          onLayout={(event) => {
+            secondLayout.resolve(toLayout(event))
+          }}
+          onPreviewStarted={callback(secondPreviewStarted.resolve)}
+        />,
+      )
+
+      const secondPreview = await withTimeout(
+        secondRef.promise,
+        10_000,
+        'second NativePreviewView hybridRef',
+      )
+      const secondPreviewLayout = await withTimeout(
+        secondLayout.promise,
+        10_000,
+        'second NativePreviewView onLayout',
+      )
+      await withTimeout(
+        secondPreviewStarted.promise,
+        15_000,
+        'second NativePreviewView onPreviewStarted',
+      )
+      expectPreviewGeometry(secondPreview, secondPreviewLayout)
+    } finally {
+      errorSub.remove()
+      await session.stop()
+    }
+  })
+
   it('starts a replacement preview and stops the removed preview while running', async () => {
     const session = await VisionCamera.createCameraSession(false)
     const firstPreviewOutput = VisionCamera.createPreviewOutput()

packages/react-native-vision-camera/android/src/main/java/com/margelo/nitro/camera/views/HybridPreviewView.kt

@@ -37,7 +37,10 @@ class HybridPreviewView(
 ) : HybridPreviewViewSpec(),
   View.OnTouchListener,
   Observer<PreviewView.StreamState> {
-  private val previewView = PreviewView(context)
+  // released on drop; JS may hold this object long after unmount
+  private var previewViewOrNull: PreviewView? = PreviewView(context)
+  private val previewView: PreviewView
+    get() = previewViewOrNull ?: throw Error("PreviewView has already been dropped from the React tree!")
   private val uiScope = CoroutineScope(Dispatchers.Main.immediate)
   override val view: View
     get() = previewView
@@ -67,6 +70,7 @@ class HybridPreviewView(
         field = newImplementationMode
         uiScope.launch {
           // Update ImplementationMode and reconnect output
+          val previewView = previewViewOrNull ?: return@launch
           previewView.implementationMode = newImplementationMode.toImplementationMode()
           previewOutput?.let { previewOutput -> connectPreviewOutput(previewOutput) }
         }
@@ -80,6 +84,7 @@ class HybridPreviewView(
         field = newResizeMode
         uiScope.launch {
           // Update scaleType
+          val previewView = previewViewOrNull ?: return@launch
           previewView.scaleType = newResizeMode.toScaleType()
         }
       }
@@ -100,9 +105,30 @@ class HybridPreviewView(
     pixelRatio = context.resources.displayMetrics.density
   }
 
+  override fun onDropView() {
+    super.onDropView()
+    uiScope.launch {
+      releasePreviewView()
+    }
+  }
+
   override fun dispose() {
     super.dispose()
+    uiScope.launch {
+      releasePreviewView()
+    }
+  }
+
+  /**
+   * Detaches the `PreviewView` from its Preview Output and releases it.
+   * Safe to call from both `onDropView()` and `dispose()`.
+   */
+  @UiThread
+  private fun releasePreviewView() {
+    val previewView = previewViewOrNull ?: return
     previewView.previewStreamState.removeObserver(this)
+    previewOutput?.let { previewOutput -> disconnectPreviewOutput(previewOutput) }
+    previewViewOrNull = null
   }
 
   override fun createMeteringPoint(
@@ -168,15 +194,19 @@ class HybridPreviewView(
   private fun connectPreviewOutput(previewOutput: HybridCameraPreviewOutputSpec) {
     // 1. Downcast
     val previewOutput = previewOutput as? NativePreviewOutput ?: throw Error("PreviewOutput is not of type `NativePreviewOutput`!")
-    // 2. Set surfaceProvider on UI Thread
+    // 2. Skip if the PreviewView was already dropped
+    val previewView = previewViewOrNull ?: return
+    // 3. Set surfaceProvider on UI Thread
     previewOutput.setSurfaceProvider(previewView.surfaceProvider)
   }
 
   @UiThread
   private fun disconnectPreviewOutput(previewOutput: HybridCameraPreviewOutputSpec) {
     // 1. Downcast
     val previewOutput = previewOutput as? NativePreviewOutput ?: throw Error("PreviewOutput is not of type `NativePreviewOutput`!")
-    // 2. Remove surfaceProvider on UI Thread
+    // 2. Skip if the PreviewView was already dropped
+    val previewView = previewViewOrNull ?: return
+    // 3. Remove surfaceProvider on UI Thread
     previewOutput.removeSurfaceProvider(previewView.surfaceProvider)
   }
 
@@ -201,7 +231,7 @@ class HybridPreviewView(
   // since it's accessible from the UI-Thread only.
   private fun updateCameraSpaceToViewPixelsMatrix() {
     val matrix =
-      previewView.sensorToViewTransform
+      previewViewOrNull?.sensorToViewTransform
         ?: return
     this.cameraSpaceToViewPixelsMatrix = matrix
   }