Android\OPhone动画分析之翻转效果

看到很多人在问如何实现三维的翻转效果，所以今天在这里简单的给大家分析一下，其实在APIDemo中就有这样一个例子，那么我们就以其为例来学习Android中的翻转动画效果的实现，首先看一下运行效果如下图所示。

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<String> adapter = new ArrayAdapter<String>(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);  
        }  
    }  
 
}