stateCallback = new CameraDevice.StateCallback() {
            @Override
            public void onOpened(CameraDevice cameraDevice) {
                CameraActivity.this.cameraDevice = cameraDevice;
                createPreviewSession();
            }

            @Override
            public void onDisconnected(CameraDevice cameraDevice) {
                cameraDevice.close();
                CameraActivity.this.cameraDevice = null;
            }

            @Override
            public void onError(CameraDevice cameraDevice, int error) {
                cameraDevice.close();
                CameraActivity.this.cameraDevice = null;
            }
        };