flutter - error in accessing camera

Question

I am creating an app in which I need to use camera of mobile device. I have created below class

class CameraWidget extends StatefulWidget {
  @override
  _CameraWidgetState createState() => _CameraWidgetState();
}

class _CameraWidgetState extends State<CameraWidget> {
  List<CameraDescription> cameras;
  CameraController controller;
  bool isReady= false;

//  @override
//  void initState() {
//    super.initState();
//    _setupCamera();
//  }

  Future<void> _setupCamera() async {
    try {
      // initialize cameras.
      cameras = await availableCameras();
      // initialize camera controllers.
      controller = new CameraController(cameras[1], ResolutionPreset.medium);
      await controller.initialize();
    } on CameraException catch (_) {
      //debugPrint("Some error occured!").
    }
    if (!mounted) return;
    setState(() {
      isReady = true;
    });
  }

  @override
  Widget build(BuildContext context) {
    return new FutureBuilder(
        future: _setupCamera(),
        builder: (BuildContext context, AsyncSnapshot snapshot) {
          if (!isReady) {
            return new Container();
          }
          return new Center(
            child: new AspectRatio(
            aspectRatio: controller.value.aspectRatio,
            child: new CameraPreview(controller))
          );
        }
    );
  }
}

I am not getting any error with above code but my application is getting exited everytime after few seconds. I am not sure what is going on.Below is the application log.

Launching lib/main.dart on Android SDK built for x86 in debug mode...
Initializing gradle...
Resolving dependencies...
Running 'gradlew assembleDebug'...
Built build/app/outputs/apk/debug/app-debug.apk.
Installing build/app/outputs/apk/app.apk...
I/FlutterActivityDelegate(17280): onResume setting current activity to this
Syncing files to device Android SDK built for x86...
I/CameraManagerGlobal(17280): Connecting to camera service
D/        (17280): HostConnection::get() New Host Connection established 0xe8b07a80, tid 17330
D/EGL_emulation(17280): eglMakeCurrent: 0xf0465a00: ver 2 0 (tinfo 0xe8b03370)
D/        (17280): HostConnection::get() New Host Connection established 0xe8b078c0, tid 17337
D/        (17280): HostConnection::get() New Host Connection established 0xe8b07540, tid 17316
D/        (17280): HostConnection::get() New Host Connection established 0xe8b07200, tid 17315
D/        (17280): HostConnection::get() New Host Connection established 0xe71fd100, tid 17350
I/zygote  (17280): Do partial code cache collection, code=30KB, data=27KB
I/zygote  (17280): After code cache collection, code=30KB, data=27KB
I/zygote  (17280): Increasing code cache capacity to 128KB
D/        (17280): HostConnection::get() New Host Connection established 0xe8b07b00, tid 17395
I/zygote  (17280): Do partial code cache collection, code=60KB, data=49KB
I/zygote  (17280): After code cache collection, code=60KB, data=49KB
I/zygote  (17280): Increasing code cache capacity to 256KB
I/zygote  (17280): Do full code cache collection, code=122KB, data=84KB
I/zygote  (17280): After code cache collection, code=116KB, data=69KB
D/        (17280): HostConnection::get() New Host Connection established 0xcb67d7c0, tid 17694
D/        (17280): HostConnection::get() New Host Connection established 0xe8b07580, tid 17695
I/zygote  (17280): Do partial code cache collection, code=121KB, data=82KB
I/zygote  (17280): After code cache collection, code=121KB, data=82KB
I/zygote  (17280): Increasing code cache capacity to 512KB
D/        (17280): HostConnection::get() New Host Connection established 0xd1360580, tid 17813
W/zygote  (17280): Long monitor contention with owner main (17280) at void android.hardware.camera2.impl.CameraDeviceImpl.close()(CameraDeviceImpl.java:1046) waiters=0 in void android.hardware.camera2.impl.CameraDeviceImpl$CameraDeviceCallbacks.onCaptureStarted(android.hardware.camera2.impl.CaptureResultExtras, long) for 142ms
W/zygote  (17280): Long monitor contention with owner main (17280) at void android.hardware.camera2.impl.CameraDeviceImpl.close()(CameraDeviceImpl.java:1046) waiters=0 in void android.hardware.camera2.impl.CameraDeviceImpl$CameraDeviceCallbacks.onResultReceived(android.hardware.camera2.impl.CameraMetadataNative, android.hardware.camera2.impl.CaptureResultExtras) for 179ms
W/zygote  (17280): Long monitor contention with owner main (17280) at void android.hardware.camera2.impl.CameraDeviceImpl.close()(CameraDeviceImpl.java:1046) waiters=0 in void android.hardware.camera2.impl.CameraDeviceImpl$CameraDeviceCallbacks.onResultReceived(android.hardware.camera2.impl.CameraMetadataNative, android.hardware.camera2.impl.CaptureResultExtras) for 150ms
W/zygote  (17280): Long monitor contention with owner main (17280) at boolean android.os.BinderProxy.transactNative(int, android.os.Parcel, android.os.Parcel, int)(Binder.java:-2) waiters=0 in void android.hardware.camera2.impl.CameraDeviceImpl$CameraDeviceCallbacks.onCaptureStarted(android.hardware.camera2.impl.CaptureResultExtras, long) for 109ms
W/zygote  (17280): Long monitor contention with owner main (17280) at boolean android.os.BinderProxy.transactNative(int, android.os.Parcel, android.os.Parcel, int)(Binder.java:-2) waiters=0 in void android.hardware.camera2.impl.CameraDeviceImpl$CameraDeviceCallbacks.onCaptureStarted(android.hardware.camera2.impl.CaptureResultExtras, long) for 130ms
Lost connection to device.

Can someone please let me know whats wrong in above code?

EDIT 1- I have analyzed it futher and found that Future builder is calling builder multiple times. I think I should add some break condiation over there. but i am not getting the same from documentation that builder will be called multiple times. But changes build method as below works properly.

  @override
  Widget build(BuildContext context) {
    if (controller == null || !controller.value.isInitialized) {
      return new Container();
    }
    return new AspectRatio(
        aspectRatio: controller.value.aspectRatio,
        child: new CameraPreview(controller));
  }

Still it will be great if someone will explain it further. I am still debugging it. :)

Answer 1

The issue here is that the Camera is being initialized by the FutureBuilder every time the screen rebuilds after calling setState(). What you can do here is use controller.value.isInitialized as a checker to verify if the Camera has been initialized before initializing the Camera. Another approach that you can consider is initializing the Camera once during initState instead of inside FutureBuilder.