Android动画分析之翻转效果（camera、gallery）

Android中并没有提供直接做3D翻转的动画，所以关于3D翻转的动画效果需要我们自己实现，那么我们首先来分析一下Animation 和 Transformation。

Animation动画的主要接口，其中主要定义了动画的 一些属性比如开始时间，持续时间，是否重复播放等等。而Transformation中则包含一个矩阵和alpha值，矩阵是用来做平移，旋转和缩放动画 的，而alpha值是用来做alpha动画的，要实现3D旋转动画我们需要继承自Animation类来实现，我们需要重载 getTransformation和applyTransformation，在getTransformation中Animation会根据动画的 属性来产生一系列的差值点，然后将这些差值点传给applyTransformation，这个函数将根据这些点来生成不同的 Transformation。下面是具体实现：

public class Rotate3dAnimation extends Animation {
    //开始角度
    private final float mFromDegrees;
    //结束角度
    private final float mToDegrees;
    //中心点
    private final float mCenterX;
    private final float mCenterY;
    private final float mDepthZ;
    //是否需要扭曲
    private final boolean mReverse;
    //摄像头
    private Camera mCamera;
    public Rotate3dAnimation(float fromDegrees, float toDegrees,
            float centerX, float centerY, float depthZ, boolean reverse) {
        mFromDegrees = fromDegrees;
        mToDegrees = toDegrees;
        mCenterX = centerX;
        mCenterY = centerY;
        mDepthZ = depthZ;
        mReverse = reverse;
    }

    @Override
    public void initialize(int width, int height, int parentWidth, int parentHeight) {
        super.initialize(width, height, parentWidth, parentHeight);
        mCamera = new Camera();
    }
    //生成Transformation
    @Override
    protected void applyTransformation(float interpolatedTime, Transformation t) {
        final float fromDegrees = mFromDegrees;
        //生成中间角度
        float degrees = fromDegrees + ((mToDegrees - fromDegrees) * interpolatedTime);

        final float centerX = mCenterX;
        final float centerY = mCenterY;
        final Camera camera = mCamera;

        final Matrix matrix = t.getMatrix();

        camera.save();
        if (mReverse) {
            camera.translate(0.0f, 0.0f, mDepthZ * interpolatedTime);
        } else {
            camera.translate(0.0f, 0.0f, mDepthZ * (1.0f - interpolatedTime));
        }
        camera.rotateY(degrees);
        //取得变换后的矩阵
        camera.getMatrix(matrix);
        camera.restore();

        matrix.preTranslate(-centerX, -centerY);
        matrix.postTranslate(centerX, centerY);
    }
}

其中包括了旋转的开始和结束角度，中心点、是否扭曲、和一 个Camera，这里我们主要分析applyTransformation函数，其中第一个参数就是通过getTransformation函数传递的差 指点，然后我们根据这个差值通过线性差值算法计算出一个中间角度degrees，Camera类是用来实现绕Y轴旋转后透视投影的，因此我们首先通过 t.getMatrix()取得当前的矩阵，然后通过camera.translate来对矩阵进行平移变换操作，camera.rotateY进行旋 转。这样我们就可以很轻松的实现3D旋转效果了，该例子的原意是通过一个列表来供用户选择要实现翻转的图像，所以我们分析至少需要定义两个控 件：ListView和ImageView（要翻转的图像），主界面的xml布局定义如下所示。

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

    <ListView
        android:id="@android:id/list"
        android:persistentDrawingCache="animation|scrolling"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layoutAnimation="@anim/layout_bottom_to_top_slide" />

    <ImageView
        android:id="@+id/picture"
        android:scaleType="fitCenter"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:visibility="gone" />

FrameLayout>

然后准备好需要的资源，在onCreate函数中准备好 ListView和ImageView，因为要旋转所以我们需要保存视图的缓存信息，通过 setPersistentDrawingCache(ViewGroup.PERSISTENT_ANIMATION_CACHE);可以设置该功能， 当我们选择列表中的图像资源后在onItemClick中将选择的资源Id对应的图像设置到ImageView中，然后通过applyRotation来 启动一个动画，前面有了Rotate3dAnimation的实现，我们要完成3D翻转动画就很简单，直接构建一个Rotate3dAnimation对 象，设置其属性（包括动画监听），这里将动画的监听设置为DisplayNextView，可以用来显示下一个视图，在其中的动画结束监听 （onAnimationEnd）中，通过一个县城SwapViews来交换两个画面，交换过程则是设置ImageView和ListView的显示相关 属性，并构建一个Rotate3dAnimation对象，对另一个界面进行旋转即可，然后启动动画，整个转换过程实际上就是将第一个界面从0度转好90 度，然后就爱你过第二个界面从90度转到0度，这样就形成了一个翻转动画，完整代码如下，我们也加入了一些必要的注解，大家也可以参考APIDemo中的 Transition3d例子。

public class Transition3d extends Activity implements
        AdapterView.OnItemClickListener, View.OnClickListener {
    //照片列表
    private ListView mPhotosList;
    private ViewGroup mContainer;
    private ImageView mImageView;

    // 照片的名字，用于显示在list中
    private static final String[] PHOTOS_NAMES = new String[] {
            "Lyon",
            "Livermore",
            "Tahoe Pier",
            "Lake Tahoe",
            "Grand Canyon",
            "Bodie"
    };

    // 资源id
    private static final int[] PHOTOS_RESOURCES = new int[] {
            R.drawable.photo1,
            R.drawable.photo2,
            R.drawable.photo3,
            R.drawable.photo4,
            R.drawable.photo5,
            R.drawable.photo6
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.animations_main_screen);

        mPhotosList = (ListView) findViewById(android.R.id.list);
        mImageView = (ImageView) findViewById(R.id.picture);
        mContainer = (ViewGroup) findViewById(R.id.container);

        // 准备ListView
        final ArrayAdapter adapter = new ArrayAdapter(this,
                android.R.layout.simple_list_item_1, PHOTOS_NAMES);

        mPhotosList.setAdapter(adapter);
        mPhotosList.setOnItemClickListener(this);

        // 准备ImageView
        mImageView.setClickable(true);
        mImageView.setFocusable(true);
        mImageView.setOnClickListener(this);

        //设置需要保存缓存
        mContainer.setPersistentDrawingCache(ViewGroup.PERSISTENT_ANIMATION_CACHE);
    }

    /**
     * Setup a new 3D rotation on the container view.
     *
     * @param position the item that was clicked to show a picture, or -1 to show the list
     * @param start the start angle at which the rotation must begin
     * @param end the end angle of the rotation
     */
    private void applyRotation(int position, float start, float end) {
        // 计算中心点
        final float centerX = mContainer.getWidth() / 2.0f;
        final float centerY = mContainer.getHeight() / 2.0f;

        // Create a new 3D rotation with the supplied parameter
        // The animation listener is used to trigger the next animation
        final Rotate3dAnimation rotation =
                new Rotate3dAnimation(start, end, centerX, centerY, 310.0f, true);
        rotation.setDuration(500);
        rotation.setFillAfter(true);
        rotation.setInterpolator(new AccelerateInterpolator());
        //设置监听
        rotation.setAnimationListener(new DisplayNextView(position));

        mContainer.startAnimation(rotation);
    }

    public void onItemClick(AdapterView parent, View v, int position, long id) {
        // 设置ImageView
        mImageView.setImageResource(PHOTOS_RESOURCES[position]);
        applyRotation(position, 0, 90);
    }
    //点击图像时，返回listview
    public void onClick(View v) {
        applyRotation(-1, 180, 90);
    }

    /**
     * This class listens for the end of the first half of the animation.
     * It then posts a new action that effectively swaps the views when the container
     * is rotated 90 degrees and thus invisible.
     */
    private final class DisplayNextView implements Animation.AnimationListener {
        private final int mPosition;

        private DisplayNextView(int position) {
            mPosition = position;
        }

        public void onAnimationStart(Animation animation) {
        }
        //动画结束
        public void onAnimationEnd(Animation animation) {
            mContainer.post(new SwapViews(mPosition));
        }

        public void onAnimationRepeat(Animation animation) {
        }
    }

    /**
     * This class is responsible for swapping the views and start the second
     * half of the animation.
     */
    private final class SwapViews implements Runnable {
        private final int mPosition;

        public SwapViews(int position) {
            mPosition = position;
        }

        public void run() {
            final float centerX = mContainer.getWidth() / 2.0f;
            final float centerY = mContainer.getHeight() / 2.0f;
            Rotate3dAnimation rotation;

            if (mPosition > -1) {
                //显示ImageView
                mPhotosList.setVisibility(View.GONE);
                mImageView.setVisibility(View.VISIBLE);
                mImageView.requestFocus();

                rotation = new Rotate3dAnimation(90, 180, centerX, centerY, 310.0f, false);
            } else {
                //返回listview
                mImageView.setVisibility(View.GONE);
                mPhotosList.setVisibility(View.VISIBLE);
                mPhotosList.requestFocus();

                rotation = new Rotate3dAnimation(90, 0, centerX, centerY, 310.0f, false);
            }

            rotation.setDuration(500);
            rotation.setFillAfter(true);
            rotation.setInterpolator(new DecelerateInterpolator());
            //开始动画
            mContainer.startAnimation(rotation);
        }
    }

}