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：1.public class Rotate3dAnimation extends Animation {2.//开始角度3. private final float mFromDegrees;4.//结束角度5. private final float mToDegrees;6.//中心点7. private final float mCenterX;8. private final float mCenterY;9. private final float mDepthZ;10.//是否需要扭曲11. private final boolean mReverse;12.//摄像头13. private Camera mCamera;14. public Rotate3dAnimation(float fromDegrees, float toDegrees,15. float centerX, float centerY, float depthZ, boolean reverse) {16. mFromDegrees = fromDegrees;17. mToDegrees = toDegrees;18. mCenterX = centerX;19. mCenterY = centerY;20. mDepthZ = depthZ;21. mReverse = reverse;22. }23.24. @Override25. public void initialize(int width, int height, int parentWidth, int parentHeight) {26. super.initialize(width, height, parentWidth, parentHeight);27. mCamera = new Camera();28. }29.//生成Transformation30. @Override31. protected void applyTransformation(float interpolatedTime, Transformation t) {32. final float fromDegrees = mFromDegrees;33.//生成中间角度34. float degrees = fromDegrees + ((mToDegrees - fromDegrees) * interpolatedTime);35.36. final float centerX = mCenterX;37. final float centerY = mCenterY;38. final Camera camera = mCamera;39.40. final Matrix matrix = t.getMatrix();41.42. camera.save();43. if (mReverse) {44. camera.translate(0.0f, 0.0f, mDepthZ * interpolatedTime);45. } else {46. camera.translate(0.0f, 0.0f, mDepthZ * (1.0f - interpolatedTime));47. }48. camera.rotateY(degrees);49.//取得变换后的矩阵50. camera.getMatrix(matrix);51. camera.restore();52.53. matrix.preTranslate(-centerX, -centerY);54. matrix.postTranslate(centerX, centerY);55. }56.}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。

1.<FrameLayout xmlns:android="/apk/res/android"2. android:id="@+id/container"3. android:layout_width="match_parent"4. android:layout_height="match_parent">5.6. <ListView7. android:id="@android:id/list"8. android:persistentDrawingCache="animation|scrolling"9. android:layout_width="match_parent"10. android:layout_height="match_parent"11. android:layoutAnimation="@anim/layout_bottom_to_top_slide" />12.13. <ImageView14. android:id="@+id/picture"15. android:scaleType="fitCenter"16. android:layout_width="match_parent"17. android:layout_height="match_parent"18. android:visibility="gone" />19.20.</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。

1.public class Transition3d extends Activity implements2. AdapterView.OnItemClickListener, View.OnClickListener {3.//照片列表4. private ListView mPhotosList;5. private ViewGroup mContainer;6. private ImageView mImageView;7.8.// 照片的名字，用于显示在list中9. private static final String[] PHOTOS_NAMES = new String[] {10. "Lyon",11. "Livermore",12. "Tahoe Pier",13. "Lake Tahoe",14. "Grand Canyon",15. "Bodie"16. };17.18.// 资源id19. private static final int[] PHOTOS_RESOURCES = new int[] {20. R.drawable.photo1,21. R.drawable.photo2,22. R.drawable.photo3,23. R.drawable.photo4,24. R.drawable.photo5,25. R.drawable.photo626. };27.28. @Override29. protected void onCreate(Bundle savedInstanceState) {30. super.onCreate(savedInstanceState);31.32. setContentView(yout.animations_main_screen);33.34. mPhotosList = (ListView) findViewById(android.R.id.list);35. mImageView = (ImageView) findViewById(R.id.picture);36. mContainer = (ViewGroup) findViewById(R.id.container);37.38.// 准备ListView39. final ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,40. yout.simple_list_item_1, PHOTOS_NAMES);41.42. mPhotosList.setAdapter(adapter);43. mPhotosList.setOnItemClickListener(this);44.45.// 准备ImageView46. mImageView.setClickable(true);47. mImageView.setFocusable(true);48. mImageView.setOnClickListener(this);49.50.//设置需要保存缓存51. mContainer.setPersistentDrawingCache(ViewGroup.PERSISTENT_ANIMATION_CACHE);52. }53.54./**55. * Setup a new 3D rotation on the container view.56. *57. * @param position the item that was clicked to show a picture, or -1to show the list58. * @param start the start angle at which the rotation must begin59. * @param end the end angle of the rotation60. */61. private void applyRotation(int position, float start, float end) {62.// 计算中心点63. final float centerX = mContainer.getWidth() / 2.0f;64. final float centerY = mContainer.getHeight() / 2.0f;65.66.// Create a new 3D rotation with the supplied parameter67.// The animation listener is used to trigger the next animation68. final Rotate3dAnimation rotation =69. new Rotate3dAnimation(start, end, centerX, centerY, 310.0f, true);70. rotation.setDuration(500);71. rotation.setFillAfter(true);72. rotation.setInterpolator(new AccelerateInterpolator());73.//设置监听74. rotation.setAnimationListener(new DisplayNextView(position));75.76. mContainer.startAnimation(rotation);77. }78.79. public void onItemClick(AdapterView parent, View v, int position, longid) {80.// 设置ImageView81. mImageView.setImageResource(PHOTOS_RESOURCES[position]);82. applyRotation(position, 0, 90);83. }84.//点击图像时，返回listview85. public void onClick(View v) {86. applyRotation(-1, 180, 90);87. }88.89./**90. * This class listens for the end of the first half of the animation.91. * It then posts a new action that effectively swaps the views when the container92. * is rotated 90 degrees and thus invisible.93. */94. private final class DisplayNextView implements Animation.AnimationListener {95. private final int mPosition;96.97. private DisplayNextView(int position) {98. mPosition = position;99. }100.101. public void onAnimationStart(Animation animation) {102. }103.//动画结束104. public void onAnimationEnd(Animation animation) {105. mContainer.post(new SwapViews(mPosition));106. }107.108. public void onAnimationRepeat(Animation animation) {109. }110. }111.112./**113. * This class is responsible for swapping the views and start the second114. * half of the animation.115. */116. private final class SwapViews implements Runnable {117. private final int mPosition;118.119. public SwapViews(int position) {120. mPosition = position;121. }122.123. public void run() {124. final float centerX = mContainer.getWidth() / 2.0f; 125. final float centerY = mContainer.getHeight() / 2.0f; 126. Rotate3dAnimation rotation;127.128. if (mPosition > -1) {129.//显示ImageView130. mPhotosList.setVisibility(View.GONE);131. mImageView.setVisibility(View.VISIBLE);132. mImageView.requestFocus();133.134. rotation = new Rotate3dAnimation(90, 180, centerX, c enterY, 310.0f, false);135. } else {136.//返回listview137. mImageView.setVisibility(View.GONE);138. mPhotosList.setVisibility(View.VISIBLE);139. mPhotosList.requestFocus();140.141. rotation = new Rotate3dAnimation(90, 0, centerX, cen terY, 310.0f, false);142. }143.144. rotation.setDuration(500);145. rotation.setFillAfter(true);146. rotation.setInterpolator(new DecelerateInterpolator()); 147.//开始动画148. mContainer.startAnimation(rotation); 149. }150. }151.152.}。