[camera] Add null check before starting preview

packages/camera/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 0.5.8+11
+
+* Fix rare nullptr exception on Android.
+* Updated README.md with information about handling App lifecycle changes.
+
 ## 0.5.8+10
 
 * Suppress the `deprecated_member_use` warning in the example app for `ScaffoldMessenger.showSnackBar`.

packages/camera/README.md

@@ -41,6 +41,27 @@ Change the minimum Android sdk version to 21 (or higher) in your `android/app/bu
 minSdkVersion 21
 ```
 
+### Handling Lifecycle states
+
+As of version [0.5.0](https://github.com/flutter/plugins/blob/master/packages/camera/CHANGELOG.md#050) of the camera plugin, lifecycle changes are no longer handled by the plugin. This means developers are now responsible to control camera resources when the lifecycle state is updated. Failure to do so might lead to unexpected behavior (for example as described in issue [#39109](https://github.com/flutter/flutter/issues/39109)). Handling lifecycle changes can be done by overriding the `didChangeAppLifecycleState` method like so:
+
+```dart
+  @override
+  void didChangeAppLifecycleState(AppLifecycleState state) {
+    // App state changed before we got the chance to initialize.
+    if (controller == null || !controller.value.isInitialized) {
+      return;
+    }
+    if (state == AppLifecycleState.inactive) {
+      controller?.dispose();
+    } else if (state == AppLifecycleState.resumed) {
+      if (controller != null) {
+        onNewCameraSelected(controller.description);
+      }
+    }
+  }
+```
+
 ### Example
 
 Here is a small example flutter app displaying a full screen camera preview.

packages/camera/android/src/main/java/io/flutter/plugins/camera/Camera.java

@@ -410,6 +410,8 @@ public void resumeVideoRecording(@NonNull final Result result) {
   }
 
   public void startPreview() throws CameraAccessException {
+    if (pictureImageReader == null || pictureImageReader.getSurface() == null) return;
+
     createCaptureSession(CameraDevice.TEMPLATE_PREVIEW, pictureImageReader.getSurface());
   }
 

packages/camera/pubspec.yaml

@@ -2,7 +2,7 @@ name: camera
 description: A Flutter plugin for getting information about and controlling the
   camera on Android and iOS. Supports previewing the camera feed, capturing images, capturing video,
   and streaming image buffers to dart.
-version: 0.5.8+10
+version: 0.5.8+11
 
 homepage: https://github.com/flutter/plugins/tree/master/packages/camera