Android实现3D翻转动画效果

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：

package com.example.textviewtest; 
 
import android.graphics.Camera; 
import android.graphics.Matrix; 
import android.view.animation.Animation; 
import android.view.animation.Transformation; 
 
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。

下面是布局文件main.xml:

MainActivity的代码如下：

package com.example.textviewtest; 
 
import android.app.Activity; 
import android.os.Bundle; 
import android.view.Menu; 
import android.view.View; 
import android.view.animation.AccelerateInterpolator; 
import android.view.animation.Animation; 
import android.view.animation.DecelerateInterpolator; 
import android.widget.Button; 
import android.widget.TextView; 
 
public class MainActivity extends Activity { 
  private TextView tv; 
  private Button btn; 
  private int count = 1; 
 
  @Override 
  protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    tv = (TextView) findViewById(R.id.tv); 
    tv.setText(String.valueOf(count)); 
    btn = (Button) findViewById(R.id.next_btn); 
    applyRotation(0, 90); 
 
    btn.setonClickListener(new View.onClickListener() { 
 
      @Override 
      public void onClick(View v) { 
 applyRotation(0, 90); 
      } 
    }); 
 
  } 
 
  private void applyRotation(float start, float end) { 
    // 计算中心点 
    final float centerX = tv.getWidth() / 2.0f; 
    final float centerY = tv.getHeight() / 2.0f; 
 
    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()); 
 
    tv.startAnimation(rotation); 
  } 
 
  private final class DisplayNextView implements Animation.AnimationListener { 
 
    public void onAnimationStart(Animation animation) { 
    } 
 
    // 动画结束 
    public void onAnimationEnd(Animation animation) { 
      tv.post(new SwapViews()); 
    } 
 
    public void onAnimationRepeat(Animation animation) { 
    } 
  } 
 
  private final class SwapViews implements Runnable { 
 
    public void run() { 
      final float centerX = tv.getWidth() / 2.0f; 
      final float centerY = tv.getHeight() / 2.0f; 
      Rotate3dAnimation rotation = null; 
 
      tv.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 
      tv.startAnimation(rotation); 
      tv.setText(String.valueOf(count++)); 
    } 
  } 
 
  @Override 
  public boolean onCreateOptionsMenu(Menu menu) { 
    getMenuInflater().inflate(R.menu.activity_main, menu); 
    return true; 
  } 
 
} 

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