Android動畫分析之3D翻轉效果

 

原博文：http://yarin.blog.51cto.com/1130898/386219

看到很多人在問如何實現三維的翻轉效果，所以今天在這裏簡單的給大家分析一下，其實在APIDemo中就有這樣一個例子，那麼我們就以其爲例來學習Android中的翻轉動畫效果的實現，首先看一下運行效果如下圖所示。

Android中並沒有提供直接做3D翻轉的動畫，所以關於3D翻轉的動畫效果需要我們自己實現，那麼我們首先來分析一下Animation 和 Transformation。

Animation動畫的主要接口，其中主要定義了動畫的一些屬性比如開始時間，持續時間，是否重複播放等等。而Transformation中則包含一個矩陣和alpha值，矩陣是用來做平移，旋轉和縮放動畫的，而alpha值是用來做alpha動畫的，要實現3D旋轉動畫我們需要繼承自Animation類來實現，我們需要重載getTransformation和applyTransformation，在getTransformation中Animation會根據動畫的屬性來產生一系列的差值點，然後將這些差值點傳給applyTransformation，這個函數將根據這些點來生成不同的Transformation。下面是具體實現：

public class Rotate3dAnimation extends Animation {
    //開始角度
    private final float mFromDegrees;
    //結束角度
    private final float mToDegrees;
    //中心點
    private final float mCenterX;
    private final float mCenterY;
    private final float mDepthZ;
    //是否需要扭曲
    private final boolean mReverse;
    //攝像頭
    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;
        //生成中間角度
        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);
        //取得變換後的矩陣
        camera.getMatrix(matrix);
        camera.restore();

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

其中包括了旋轉的開始和結束角度，中心點、是否扭曲、和一個Camera，這裏我們主要分析applyTransformation函數，其中第一個參數就是通過getTransformation函數傳遞的差指點，然後我們根據這個差值通過線性差值算法計算出一箇中間角度degrees，Camera類是用來實現繞Y軸旋轉後透視投影的，因此我們首先通過t.getMatrix()取得當前的矩陣，然後通過camera.translate來對矩陣進行平移變換操作，camera.rotateY進行旋轉。這樣我們就可以很輕鬆的實現3D旋轉效果了，該例子的原意是通過一個列表來供用戶選擇要實現翻轉的圖像，所以我們分析至少需要定義兩個控件：ListView和ImageView（要翻轉的圖像），主界面的xml佈局定義如下所示。

<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>

然後準備好需要的資源，在onCreate函數中準備好ListView和ImageView，因爲要旋轉所以我們需要保存視圖的緩存信息，通過setPersistentDrawingCache(ViewGroup.PERSISTENT_ANIMATION_CACHE);可以設置該功能，當我們選擇列表中的圖像資源後在onItemClick中將選擇的資源Id對應的圖像設置到ImageView中，然後通過applyRotation來啓動一個動畫，前面有了Rotate3dAnimation的實現，我們要完成3D翻轉動畫就很簡單，直接構建一個Rotate3dAnimation對象，設置其屬性（包括動畫監聽），這裏將動畫的監聽設置爲DisplayNextView，可以用來顯示下一個視圖，在其中的動畫結束監聽（onAnimationEnd）中，通過一個縣城SwapViews來交換兩個畫面，交換過程則是設置ImageView和ListView的顯示相關屬性，並構建一個Rotate3dAnimation對象，對另一個界面進行旋轉即可，然後啓動動畫，整個轉換過程實際上就是將第一個界面從0度轉好90度，然後就愛你過第二個界面從90度轉到0度，這樣就形成了一個翻轉動畫，完整代碼如下，我們也加入了一些必要的註解，大家也可以參考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，用於顯示在list中
    private static final String[] PHOTOS_NAMES = new String[] {
            "Lyon",
            "Livermore",
            "Tahoe Pier",
            "Lake Tahoe",
            "Grand Canyon",
            "Bodie"
    };

    // 資源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);

        // 準備ListView
        final ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
                android.R.layout.simple_list_item_1, PHOTOS_NAMES);

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

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

        //設置需要保存緩存
        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) {
        // 計算中心點
        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());
        //設置監聽
        rotation.setAnimationListener(new DisplayNextView(position));

        mContainer.startAnimation(rotation);
    }

    public void onItemClick(AdapterView parent, View v, int position, long id) {
        // 設置ImageView
        mImageView.setImageResource(PHOTOS_RESOURCES[position]);
        applyRotation(position, 0, 90);
    }
    //點擊圖像時，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) {
        }
        //動畫結束
        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) {
                //顯示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());
            //開始動畫
            mContainer.startAnimation(rotation);
        }
    }

}