Question

我正在做一个camara项目，其中一个活动的捕获图像被发送到另一个活动。问题是，当我点击捕获按钮时，应用程序崩溃并在logcat上显示空点异常

public class MainActivity extends Activity {

    private Camera mCamera;
    private CameraPreview mPreview;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mCamera = getCameraInstance();



        // Create the Camera preview view
        mPreview = new CameraPreview(this, mCamera);
        FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
        preview.addView(mPreview);

        final Camera.PictureCallback mPicture = new Camera.PictureCallback() {

            @Override
            public void onPictureTaken(byte[] data, Camera camera) {
                Intent intent = new Intent(MainActivity.this, EditActivity.class);
                intent.putExtra(EditActivity.EXTRA_BYTES, data);
                intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                startActivity(intent);
            }
        };

        // Add a listener to the capture button
        ImageButton captureButton = (ImageButton) findViewById(R.id.button_capture);
        captureButton.setImageDrawable(getResources().getDrawable(R.drawable.cam));
        captureButton.setOnClickListener(
                new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        mCamera.takePicture(null, null, mPicture);
                    }
                }

        );


    }


    @Override
    protected void onPause() {
        super.onPause();
        finish();
        mPreview.stopPreview();
    }

    /**
     * A safe way to get an instance of the Camera object.
     *
     * Returns null if camera is unavailable.
     */
    private static Camera getCameraInstance() {
        Camera c = null;
        try {
            c = Camera.open(Camera.CameraInfo.CAMERA_FACING_FRONT);
        } catch (Exception ignore) {
            // Camera is not available (in use or does not exist). Do nothing.
        }
        return c;
    }

    public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {

        private SurfaceHolder mHolder;
        private Camera mCamera;

        public CameraPreview(Context context, Camera camera) {
            super(context);
            mCamera = camera;

            // Install a SurfaceHolder.Callback so we get notified when the
            // underlying surface is created and destroyed.
            mHolder = getHolder();
            mHolder.addCallback(this);
            // deprecated setting, but required on Android versions prior to 3.0
            mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
        }

        public void surfaceCreated(SurfaceHolder holder) {
            // The Surface has been created, now tell the camera where to draw the preview.
            try {
                if (mCamera != null) {
                    mCamera.setDisplayOrientation(90);
                    mCamera.setPreviewDisplay(holder);
                    mCamera.startPreview();
                }
            } catch (IOException ignore) {
                // Do nothing
            }
        }

        public void surfaceDestroyed(SurfaceHolder holder) {
            if (mCamera != null) {
                mCamera.stopPreview();
            }
        }

        private void stopPreview() {
            if (mCamera != null) {
                mCamera.stopPreview();
                mCamera.release();
                mCamera = null;
            }
        }

        public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
            // If your preview can change or rotate, take care of those events here.
            // Make sure to stop the preview before resizing or reformatting it.

            if (mHolder.getSurface() == null) {
                // preview surface does not exist
                return;
            }

            // Stop preview before making changes
            try {
                mCamera.stopPreview();
            } catch (Exception ignore) {
                // Tried to stop a non-existent preview. Do nothing.
            }

            // Set preview size and make any resize, rotate or reformatting changes here

            // Start preview with new settings
            try {
                mCamera.setPreviewDisplay(mHolder);
                mCamera.startPreview();
            } catch (Exception ignore) {
                // Do nothing
            }
        }
    }
}

Answer 1

除非您为图像选择了低分辨率，否则会因为事务太大的异常而崩溃。 IPC交易的大小限制为1MB，这意味着Intent的大小限制为~1MB。大多数相机照片都会远远大于此。

您的选择是：

拍摄低分辨率图像
摆脱第二项活动并在一项活动中完成所有这项工作（例如，使用多个片段）
小心通过其他方式（例如，单身）从第一个活动到第二个活动获取图像，采取适当的步骤以避免令人讨厌的内存泄漏

Answer 2

这是您的代码崩溃的部分：

                @Override
                public void onClick(View v) {
                    mCamera.takePicture(null, null, mPicture);
                }

让我们看看它来自哪里。您有四个值：

mCamera：如果mCamera为null，则会抛出NullPointerException，因为您尝试使用未存在对象的takePicture方法
第一个和第二个参数是null。如果takePicture尝试使用这些参数的数据成员或方法，则会引发NullPointerException
mPicture可能是null。如果mPicture为null并且您尝试在takePicture中使用其中一个数据成员/方法，则会引发NullPointerException

我相信mCamera是null。如果我是对的，您应该查看如何创建相机对象：

/**
 * A safe way to get an instance of the Camera object.
 *
 * Returns null if camera is unavailable.
 */
private static Camera getCameraInstance() {
    Camera c = null;
    try {
        c = Camera.open(Camera.CameraInfo.CAMERA_FACING_FRONT);
    } catch (Exception ignore) {
        // Camera is not available (in use or does not exist). Do nothing.
    }
    return c;
}

在这里，您隐藏任何Exception。我想请你调试你的项目，看看这里是否有Exception。如果你看到给定的Exception，你很可能会意识到你的问题是什么。

Camara App在点击时崩溃

2 个答案: