尝试在空对象引用上写入字段 'android.hardware.camera2.ICameraDeviceUser

Question

我使用Camera2 为 API > 20 的设备实现相机预览。我在使用 android 5.0.0 的 asus_t00j 上遇到错误。我不确定它为什么会出现。

Fatal Exception: java.lang.NullPointerException: Attempt to write to field 'android.hardware.camera2.ICameraDeviceUser android.hardware.camera2.impl.CameraDeviceImpl.mRemoteDevice' on a null object reference
   at android.hardware.camera2.impl.CameraDeviceImpl.close(CameraDeviceImpl.java:773)
   at com.vyda.stream.screencast.CameraHelper.closeCamera(CameraHelper.java:410)
   at com.vyda.stream.screencast.CameraHelper.stopCameraAndRemoveWindow(CameraHelper.java:150)
   at com.vyda.stream.screencast.ScreencastService.endScreencasting(ScreencastService.java:307)
   at com.vyda.stream.screencast.ScreencastService$8.onClick(ScreencastService.java:275)
   at android.view.View.performClick(View.java:4756)
   at android.view.View$PerformClick.run(View.java:19761)
   at android.os.Handler.handleCallback(Handler.java:739)
   at android.os.Handler.dispatchMessage(Handler.java:95)
   at android.os.Looper.loop(Looper.java:135)
   at android.app.ActivityThread.main(ActivityThread.java:5253)
   at java.lang.reflect.Method.invoke(Method.java)
   at java.lang.reflect.Method.invoke(Method.java:372)
   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

CameraHelper::closeCamera()

private void closeCamera() {
        try {
            cameraOpenCloseLock.acquire();
            if (null != captureSession) {
                captureSession.close();
                captureSession = null;
            }
            if (null != cameraDevice) {
                cameraDevice.close();
                cameraDevice = null;
            }
        } catch (InterruptedException e) {
            throw new RuntimeException("Interrupted while trying to lock camera closing.", e);
        } finally {
            cameraOpenCloseLock.release();
        }
    }

Answer 1

captureSession.close() 是异步的，这意味着当您的代码到达cameraDevice.close() 时，底层相机对象（但不是您CameraHelper 的cameraDevice 成员）被销毁。对于captureSession.close() 和cameraDevice.close()，您应该等待onClosed() 回调。

但cameraDevice.close() 的描述说明活动会话将为您关闭，因此您不需要在您的场景中调用captureSession.close()。

PS 我相信您所遇到的是在 ASUS 设备上执行 Camera2 API 的错误。