Flip Animation for Android:

近期项目中用到了一个小动画，让物体实现一定的3D旋转效果，现记录例如以下：

public class FlipAnimation extends Animation {

    private Camera mCamera;

    private View mFromView;

    private View mToView;

    private float mCenterX;

    private float mCenterY;

    private boolean mForward = true;

    /**

     * Creates a 3D flip animation between two views.

     *

     * @param fromView First view in the transition.

     * @param toView Second view in the transition.

     */

    public FlipAnimation(View fromView, View toView) {

        mFromView = fromView;

        mToView = toView;

        setDuration(700);

        setFillAfter(false);

        setInterpolator(new AccelerateDecelerateInterpolator());

    }

    public void reverse() {

        mForward = false;

        View switchView = mToView;

        mToView = mFromView;

        mFromView = switchView;

    }

    @Override

    public void initialize(int width, int height, int parentWidth, int parentHeight) {

        super.initialize(width, height, parentWidth, parentHeight);

        mCenterX = width / 2;

        mCenterY = height / 2;

        mCamera = new Camera();

    }

    @Override

    protected void applyTransformation(float interpolatedTime, Transformation t) {

        final double radians = Math.PI * interpolatedTime;

        float degrees = (float)(180.0 * radians / Math.PI);

        if (interpolatedTime >= 0.5f) {

            degrees -= 180.f;

            mFromView.setVisibility(View.GONE);

            mToView.setVisibility(View.VISIBLE);

        }

        if (mForward) {

            degrees = -degrees;

        }

        final Matrix matrix = t.getMatrix();

        mCamera.save();

        mCamera.rotateY(degrees);

        mCamera.getMatrix(matrix);

        mCamera.restore();

        matrix.preTranslate(-mCenterX, -mCenterY);

        matrix.postTranslate(mCenterX, mCenterY);

    }

}