Android 動畫分析之翻轉效果

Android中並無提供直接作3D翻轉的動畫，因此關於3D翻轉的動畫效果須要咱們本身實現，那麼咱們首先來分析一下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好比開始時間，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，矩陣是用來作平移，旋轉和縮放動畫的，而alpha值是用來作alpha動畫的，要實現3D旋轉動畫咱們須要繼承自Animation類來實現，咱們須要重載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，而後將這些差值點傳給applyTransformation，這個函數將根據這些點來生成不一樣的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;  
    //是否須要扭曲  
    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，這裏咱們主要分析applyTransformation函數，其中第一個參數就是經過getTransformation函數傳遞的差指點，而後咱們根據這個差值經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，所以咱們首先經過t.getMatrix()取得當前的矩陣，而後經過camera.translate來對矩陣進行平移變換操做，camera.rotateY進行旋轉。這樣咱們就能夠很輕鬆的實現3D旋轉效果了，該例子的原意是經過一個列表來供用戶選擇要實現翻轉的圖像，因此咱們分析至少須要定義兩個控件：ListView和ImageView（要翻轉的圖像），主界面的xml佈局定義以下所示。

<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>

而後準備好須要的資源，在onCreate函數中準備好ListView和ImageView，由於要旋轉因此咱們須要保存視圖的緩存信息，經過setPersistentDrawingCache(ViewGroup.PERSISTENT_ANIMATION_CACHE);能夠設置該功能，當咱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，而後經過applyRotation來啓動一個動畫，前面有了Rotate3dAnimation的實現，咱們要完成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，能夠用來顯示下一個視圖，在其中的動畫結束監聽（onAnimationEnd）中，經過一個縣城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，對另外一個界面進行旋轉便可，而後啓動動畫，整個轉換過程實際上就是將第一個界面從0度轉好90度，而後就愛你過第二個界面從90度轉到0度，這樣就造成了一個翻轉動畫，完整代碼以下，咱們也加入了一些必要的註解，你們也能夠參考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);  
 
        //設置須要保存緩存  
        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);  
        }  
    }  
 
}