Android动画分析之3D翻转效果

Android中的翻转动画效果的实现，首先看一下运行效果如上图所示.

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：

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:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/main_screen_bg"
    android:gravity="center_horizontal"
    android:orientation="vertical"
    tools:context=".MainActivity" >

    <Button
        android:id="@+id/next_btn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="20dip"
        android:drawableTop="@drawable/qiangpiao_dropdown"
        android:text="下一个" />

    <TextView
        android:id="@+id/tv"
        android:layout_width="300dip"
        android:layout_height="300dip"
        android:layout_gravity="center"
        android:background="@drawable/call_show_frame_safe"
        android:gravity="center"
        android:textColor="#ffffff"
        android:textSize="15sp" />

</LinearLayout>

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;
    }

}

看懂了吗？呵呵。