View中的getRotation方法有什么作用

View中的getRotation方法用于获取视图的旋转角度。它返回一个浮点数值，表示视图相对于其父容器的旋转角度。默认情况下，视图的旋转角度为0，表示未进行任何旋转。可以通过setRotation方法来设置视图的旋转角度。getRotation方法对于需要根据视图的旋转状态进行相应操作或动画效果的开发非常有用。

相关问题

读取系统相机拍照并将其在Recycler view中显示

首先，你需要请求相机权限，可以使用以下代码：

private static final int REQUEST_CAMERA_PERMISSION = 1;

if (ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA)
        != PackageManager.PERMISSION_GRANTED) {
    ActivityCompat.requestPermissions(this, new String[] { Manifest.permission.CAMERA },
            REQUEST_CAMERA_PERMISSION);
}

现在，让我们创建一个布局文件来显示我们的相机预览和拍照按钮：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextureView
        android:id="@+id/texture_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <Button
        android:id="@+id/capture_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal|bottom"
        android:text="Capture" />

</FrameLayout>

接下来，我们需要配置相机并显示相机预览。在 onCreate 方法中，我们可以使用以下代码进行配置：

private CameraDevice cameraDevice;
private Size previewSize;
private TextureView textureView;

private CameraDevice.StateCallback stateCallback = new CameraDevice.StateCallback() {
    @Override
    public void onOpened(CameraDevice camera) {
        cameraDevice = camera;
        createCameraPreview();
    }

    @Override
    public void onDisconnected(CameraDevice camera) {
        cameraDevice.close();
    }

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

private void openCamera() {
    CameraManager manager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
    try {
        String cameraId = manager.getCameraIdList()[0];
        CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId);
        StreamConfigurationMap map = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
        previewSize = map.getOutputSizes(SurfaceTexture.class)[0];

        if (ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA)
                == PackageManager.PERMISSION_GRANTED) {
            manager.openCamera(cameraId, stateCallback, null);
        }
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}

private void createCameraPreview() {
    try {
        SurfaceTexture texture = textureView.getSurfaceTexture();
        texture.setDefaultBufferSize(previewSize.getWidth(), previewSize.getHeight());
        Surface surface = new Surface(texture);

        final CaptureRequest.Builder builder
                = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
        builder.addTarget(surface);

        cameraDevice.createCaptureSession(Arrays.asList(surface),
                new CameraCaptureSession.StateCallback() {
                    @Override
                    public void onConfigured(CameraCaptureSession session) {
                        if (cameraDevice == null) {
                            return;
                        }

                        try {
                            CaptureRequest request = builder.build();
                            session.setRepeatingRequest(request, null, null);
                        } catch (CameraAccessException e) {
                            e.printStackTrace();
                        }
                    }

                    @Override
                    public void onConfigureFailed(CameraCaptureSession session) {

                    }
                }, null);
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}

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

    textureView = findViewById(R.id.texture_view);
    openCamera();
}

现在，我们已经成功地配置了相机并显示了相机预览。接下来，我们需要实现拍照功能。在 MainActivity 中，我们可以使用以下代码实现拍照：

private static final int REQUEST_IMAGE_CAPTURE = 2;

private void takePicture() {
    if (cameraDevice == null) {
        return;
    }

    CameraManager manager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
    try {
        CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraDevice.getId());
        Size[] jpegSizes = null;
        if (characteristics != null) {
            jpegSizes = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP)
                    .getOutputSizes(ImageFormat.JPEG);
        }

        int width = 640;
        int height = 480;
        if (jpegSizes != null && jpegSizes.length > 0) {
            width = jpegSizes[0].getWidth();
            height = jpegSizes[0].getHeight();
        }

        ImageReader reader = ImageReader.newInstance(width, height, ImageFormat.JPEG, 1);
        List<Surface> outputSurfaces = new ArrayList<>(2);
        outputSurfaces.add(reader.getSurface());
        outputSurfaces.add(new Surface(textureView.getSurfaceTexture()));

        final CaptureRequest.Builder captureBuilder
                = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
        captureBuilder.addTarget(reader.getSurface());
        captureBuilder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);

        int rotation = getWindowManager().getDefaultDisplay().getRotation();
        captureBuilder.set(CaptureRequest.JPEG_ORIENTATION, getOrientation(rotation));

        ImageReader.OnImageAvailableListener readerListener = new ImageReader.OnImageAvailableListener() {
            @Override
            public void onImageAvailable(ImageReader reader) {
                Image image = null;
                try {
                    image = reader.acquireLatestImage();
                    ByteBuffer buffer = image.getPlanes()[0].getBuffer();
                    byte[] bytes = new byte[buffer.capacity()];
                    buffer.get(bytes);
                    save(bytes);
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                } finally {
                    if (image != null) {
                        image.close();
                    }
                }
            }

            private void save(byte[] bytes) throws IOException {
                OutputStream output = null;
                try {
                    File file = new File(Environment.getExternalStorageDirectory() + "/pic.jpg");
                    output = new FileOutputStream(file);
                    output.write(bytes);
                } finally {
                    if (output != null) {
                        output.close();
                    }
                }
            }
        };

        reader.setOnImageAvailableListener(readerListener, null);

        final CameraCaptureSession.CaptureCallback captureListener
                = new CameraCaptureSession.CaptureCallback() {
            @Override
            public void onCaptureCompleted(CameraCaptureSession session, CaptureRequest request,
                                           TotalCaptureResult result) {
                super.onCaptureCompleted(session, request, result);
                Toast.makeText(MainActivity.this, "Saved:" + Environment.getExternalStorageDirectory() + "/pic.jpg",
                        Toast.LENGTH_LONG).show();
                createCameraPreview();
            }
        };

        cameraDevice.createCaptureSession(outputSurfaces, new CameraCaptureSession.StateCallback() {
            @Override
            public void onConfigured(CameraCaptureSession session) {
                try {
                    session.capture(captureBuilder.build(), captureListener, null);
                } catch (CameraAccessException e) {
                    e.printStackTrace();
                }
            }

            @Override
            public void onConfigureFailed(CameraCaptureSession session) {

            }
        }, null);
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}

private int getOrientation(int rotation) {
    return (ORIENTATIONS.get(rotation) + sensorOrientation + 270) % 360;
}

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

    textureView = findViewById(R.id.texture_view);

    Button captureButton = findViewById(R.id.capture_button);
    captureButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            takePicture();
        }
    });

    openCamera();
}

现在，我们已经成功地实现了拍照功能并将图像保存到设备上。接下来，我们可以使用 RecyclerView 显示所有拍摄的照片。

onTouchEvent里的setRotation方法怎样用

在 Android 中，`setRotation()` 方法用于设置一个 View 的旋转角度。它会影响该 View 及其子 View 的绘制和布局。

在 `onTouchEvent()` 方法中使用 `setRotation()` 方法可以让我们根据手指触摸位置来旋转一个 View。例如，我们可以创建一个自定义 View，并在 `onTouchEvent()` 方法中根据手指移动的位置来旋转它。示例代码如下：

public class CustomView extends View {

    private float lastRotation = 0f;

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getActionMasked()) {
            case MotionEvent.ACTION_DOWN:
                lastRotation = getRotation();
                break;
            case MotionEvent.ACTION_MOVE:
                float rotation = event.getX() - lastRotation;
                setRotation(rotation);
                break;
            case MotionEvent.ACTION_UP:
                break;
            default:
                return false;
        }
        return true;
    }
}

在上面的代码中，我们记录了上一个旋转角度 `lastRotation`，并在 `ACTION_DOWN` 事件中将其设置为当前 View 的旋转角度。在 `ACTION_MOVE` 事件中，我们计算出手指移动的距离 `rotation`，并将其传递给 `setRotation()` 方法来旋转 View。最后，在 `ACTION_UP` 事件中我们可以做一些清理工作。

需要注意的是，`setRotation()` 方法的参数是一个浮点数，表示旋转的角度。正值表示顺时针旋转，负值表示逆时针旋转。